Luhn test of credit card numbers
The Luhn test is used by some credit card companies to distinguish valid credit card numbers from what could be a random selection of digits.
You are encouraged to solve this task according to the task description, using any language you may know.
Those companies using credit card numbers that can be validated by the Luhn test have numbers that pass the following test:
- Reverse the order of the digits in the number.
- Take the first, third, ... and every other odd digit in the reversed digits and sum them to form the partial sum s1
- Taking the second, fourth ... and every other even digit in the reversed digits:
- Multiply each digit by two and sum the digits if the answer is greater than nine to form partial sums for the even digits
- Sum the partial sums of the even digits to form s2
- If s1 + s2 ends in zero then the original number is in the form of a valid credit card number as verified by the Luhn test.
For example, if the trial number is 49927398716:
Reverse the digits:
61789372994
Sum the odd digits:
6 + 7 + 9 + 7 + 9 + 4 = 42 = s1
The even digits:
1, 8, 3, 2, 9
Two times each even digit:
2, 16, 6, 4, 18
Sum the digits of each multiplication:
2, 7, 6, 4, 9
Sum the last:
2 + 7 + 6 + 4 + 9 = 28 = s2
s1 + s2 = 70 which ends in zero which means that 49927398716 passes the Luhn test
- Task
Write a function/method/procedure/subroutine that will validate a number with the Luhn test, and
use it to validate the following numbers:
49927398716 49927398717 1234567812345678 1234567812345670
- Related tasks
11l
<lang 11l>F luhn(n)
V ch = String(n)
V sum = 0
V chParity = ch.len % 2
L(i) (ch.len-1 .. 0).step(-1)
V j = Int(ch[i])
I (i + 1) % 2 != chParity
j *= 2
I j > 9
j -= 9
sum += j
R sum % 10 == 0
L(n) (49927398716,
49927398717,
1234567812345678,
1234567812345670)
print(luhn(n))</lang>
- Output:
1B 0B 0B 1B
360 Assembly
For maximum compatibility, this program uses only the basic instruction set (S/360) and an ASSIST macro (XPRNT) to keep the code as short as possible. <lang 360asm>* Luhn test of credit card numbers 22/05/2016 LUHNTEST CSECT
USING LUHNTEST,R13 base register
B 72(R15) skip savearea
DC 17F'0' savearea
STM R14,R12,12(R13) prolog
ST R13,4(R15) "
ST R15,8(R13) "
LR R13,R15 "
LA R9,T @t(k)
LA R8,N for n
LOOPK EQU * for k=1 to n
LR R4,R9 @t(k),@s[1]
LA R6,1 from i=1
LA R7,M to m
LOOPI1 CR R6,R7 for i=1 to m
BH ELOOPI1 leave i
CLI 0(R4),C' ' if mid(s,i,1)=" "
BNE ITERI1 then
BCTR R6,0 i-1
ST R6,L l=i-1
B ELOOPI1 exit for
- end if
ITERI1 LA R4,1(R4) next @s[i]
LA R6,1(R6) i=i+1
B LOOPI1 next i
ELOOPI1 EQU * out of loop i
MVC W,BLANK w=" "
LA R4,W iw=@w
LR R5,R9 is=@s
A R5,L is=@s+l
BCTR R5,0 is=s+l-1
L R6,L i=l
LA R7,1 to 1
LOOPI2 CR R6,R7 for i=l to 1 by -1
BL ELOOPI2 leave i
MVC 0(1,R4),0(R5) mid(w,iw,1)=mid(s,is,1)
LA R4,1(R4) iw=iw+1
BCTR R5,0 is=is-1
BCTR R6,0 i=i-1
B LOOPI2 next i
ELOOPI2 EQU * out of loop i
LA R11,0 s1=0
LA R12,0 s2=0
LA R6,1 i=1
L R7,L to l
LOOPI3 CR R6,R7 for i=1 to l
BH ELOOPI3 leave i
LA R2,W-1 @w-1
AR R2,R6 w[i]
MVC CI,0(R2) ci=mid(w,i,1)
NI CI,X'0F' zap upper half byte
LR R4,R6 i
SRDA R4,32 >>32
D R4,=F'2' i/2
LTR R4,R4 if mod(i,2)>0
BNH NOTMOD then
XR R2,R2 clear
IC R2,CI z=cint(mid(w,i,1))
AR R11,R2 s1=s1+cint(mid(w,i,1))
B EIFMOD else
NOTMOD XR R2,R2 clear
IC R2,CI cint(mid(w,i,1))
SLA R2,1 *2
ST R2,Z z=cint(mid(w,i,1))*2
C R2,=F'10' if z<10
BNL GE10 then
A R12,Z s2=s2+z
B EIF10 else
GE10 L R2,Z z
CVD R2,PL8 binary to packed
UNPK CL16,PL8 packed to zoned
OI CL16+15,X'F0' zoned to char (zap sign)
MVC X(1),CL16+15 x=right(cstr(z),1)
NI X,X'0F' zap upper half byte
XR R2,R2 r2=0
IC R2,X r2=cint(right(cstr(z),1))
AR R12,R2 s2=s2+r2
LA R12,1(R12) s2=s2+cint(right(cstr(z),1))+1
EIF10 EQU * end if EIFMOD EQU * end if
LA R6,1(R6) i=i+1
B LOOPI3 next i
ELOOPI3 EQU * out of loop i
LR R1,R11 s1
AR R1,R12 s1+s2
CVD R1,PL8 binary to packed
UNPK CL16,PL8 packed to zoned
CLI CL16+15,X'C0' if right(cstr(s1+s2),1)="0"
BNE NOTZERO then
MVC R,=CL8'Valid' r="Valid"
B ECLI else
NOTZERO MVC R,=CL8'Invalid' r="Invalid" ECLI EQU * end if
MVC PG(M),0(R9) t(k)
MVC PG+M+1(L'R),R r
XPRNT PG,L'PG print buffer
LA R9,M(R9) at=at+m
BCT R8,LOOPK next k
L R13,4(0,R13) epilog
LM R14,R12,12(R13) "
XR R15,R15 "
BR R14 exit
N EQU (TEND-T)/L'T M EQU 20 T DC CL(M)'49927398716 '
DC CL(M)'49927398717 '
DC CL(M)'1234567812345678 '
DC CL(M)'1234567812345670 '
TEND DS 0C W DS CL(M) BLANK DC CL(M)' ' L DS F Z DS F PL8 DS PL8 CL16 DS CL16 CI DS C X DS C R DS CL8 PG DC CL80' ' buffer
YREGS
END LUHNTEST</lang>
- Output:
49927398716 Valid 49927398717 Invalid 1234567812345678 Invalid 1234567812345670 Valid
8080 Assembly
<lang 8080asm> org 100h jmp demo ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;; Check if the 0-terminated string at HL passes the Luhn test. ;;; Returns with carry clear if the string passes, carry set ;;; if the string fails. luhn: mvi b,0 ; Counter mov d,b ; D = S1+S2 (we don't need to keep them separate) lscan: mov a,m ; Get byte inx h ; Increment pointer inr b ; Increment counter ana a ; Is it 0? jnz lscan ; If not, try next byte dcx h ; Go to the byte before the 0 dcx h dcr b ; Decrement counter rz ; If 0, the string was empty, return. lloop: mvi c,'0' ; ASCII zero mov a,d ; Add odd digit to the total add m sub c ; Subtract ASCII zero mov d,a dcr b ; If last digit, we're done jz ldone dcx h ; Go back one byte mov a,m ; Get even digit sub c ; Subtract ASCII zero add a ; Multiply by two mvi c,9 ; 10-1, compensate for extra subtraction loop ldiv: inr c ; Find two digits using trial subtraction sui 10 jnc ldiv add c ; Add the possible second digit in add d ; Add it to the total mov d,a dcx h ; Go back one byte dcr b ; Done yet? jnz lloop ldone: mov a,d ; See if total is divisible by 10 mvi b,10 lchk: sub b ; Trial subtraction, subtract 10 rz ; If zero, it is divisible, return (carry clear) rc ; If carry, it is not divisible, return (carry set) jmp lchk ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;; Run the routine on the argument given on the CP/M command line demo: lxi h,80h ; Zero-terminate the command line argument mov a,m add l mov l,a inr l mvi m,0 mvi l,82h ; Run the 'luhn' subroutine call luhn mvi c,9 lxi d,pass ; Carry clear = print 'Pass' jnc 5 lxi d,fail ; Carry set = print 'Fail' jmp 5 pass: db 'Pass$' fail: db 'Fail$'</lang>
- Output:
A>luhn 49927398716 Pass A>luhn 49927398717 Fail A>luhn 1234567812345678 Fail A>luhn 1234567812345670 Pass
8086 Assembly
<lang asm> bits 16 cpu 8086 org 100h section .text jmp demo ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;; Check whether the 0-terminated string at DS:SI passes the Luhn ;;; test. Returns with carry clear if the string passes, carry ;;; set if the string fails. luhn: push es ; Keep original ES, and set ES=DS so SCASB can be used. push ds ; "REP DS:SCASB" is a bad idea, because the 286 has a pop es ; bug where it "forgets" the 2nd prefix if interrupted! mov di,si ; DI = pointer xor ax,ax ; Zero to test against xor bl,bl ; BL = S1+S2 mov dx,0A30h ; DH = 10 (divisor), DL = '0' (ASCII zero) xor cx,cx ; Set counter to 65535 dec cx cld ; Seek forwards repnz scasb ; Find zero dec di ; SCASB goes one byte too far xchg si,di ; SI = pointer, DI = end (or rather, beginning) mov cx,si ; CX = counter sub cx,di jcxz .done ; Empty string = stop dec si ; We don't need the zero itself std ; Seek backwards .loop: lodsb ; Get number in odd position sub al,dl ; Subtract ASCII zero add bl,al ; Add to total dec cx ; One fewer character jz .done ; No more characters = stop lodsb ; Get number in even position sub al,dl ; Subtract ASCII zero add al,al ; Multiply by two xor ah,ah ; AX = AL div dh ; Divide by 10; AL=quotient, AH=remainder add al,ah ; Add the two "digits" together add bl,al ; Add to total loop .loop ; Decrement CX and loop .done: xor ah,ah ; Divide total by 10 mov al,bl div dh and ah,ah ; If remainder 0, then return with carry clear jz .out stc ; Set carry (remainder wasn't 0, the test failed) .out: cld ; Clean up: clear direction flag, pop es ; and restore ES. ret ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;; Run the 'luhn' routine on the argument given on the MS-DOS ;;; command line. demo: mov si,80h ; Zero-terminate the argument xor bh,bh mov bl,[si] mov [si+bx+1],bh inc si inc si call luhn ; Call the routine mov ah,9 mov dx,pass ; If carry is clear, print 'Pass' jnc print mov dx,fail ; Otherwise, print 'fail' print: int 21h ret section .data pass: db 'Pass$' fail: db 'Fail$'</lang>
- Output:
C:\>luhn86 49927398716 Pass C:\>luhn86 49927398717 Fail C:\>luhn86 1234567812345678 Fail C:\>luhn86 1234567812345670 Pass
8th
<lang Forth> \ Adapted from the C version:
- remap \ n1 -- n2
[0,2,4,6,8,1,3,5,7,9] swap caseof ;
- luhn \ s -- f
0 swap s:rev ( '0 n:- swap 2 n:mod if remap then n:+ ) s:each 10 n:mod not ;
- test-luhn \ s --
dup . space luhn if "OK" else "FAIL" then . cr ;
"49927398716" test-luhn "49927398717" test-luhn "1234567812345678" test-luhn "1234567812345670" test-luhn
bye</lang>
- Output:
49927398716 OK 49927398717 FAIL 1234567812345678 FAIL 1234567812345670 OK
ABAP
<lang Abap>METHOD luhn_check.
DATA: sum(1) TYPE n VALUE 0. " Sum of checksum. DATA: current TYPE i. " Current digit. DATA: odd TYPE i VALUE 1. " Multiplier. DATA: len TYPE i. " String crowler.
" Luhn algorithm.
len = NUMOFCHAR( pi_string ) - 1.
WHILE ( len >= 0 ).
current = pi_string+len(1) * odd.
IF ( current > 9 ).
current = current - 9. " Digits sum.
ENDIF.
sum = sum + current.
odd = 3 - odd. " 1 <--> 2 Swich
len = len - 1. " Move to next charcter.
ENDWHILE.
" Validation check. IF ( sum = 0 ). pr_valid = abap_true. ELSE. pr_valid = abap_false. ENDIF.
ENDMETHOD.</lang>
ACL2
<lang Lisp>(include-book "arithmetic-3/top" :dir :system)
(defun digits (n)
(if (zp n)
nil
(cons (mod n 10)
(digits (floor n 10)))))
(defun sum (xs)
(if (endp xs)
0
(+ (first xs)
(sum (rest xs)))))
(defun double-and-sum-digits (xs)
(if (endp xs)
nil
(cons (sum (digits (* 2 (first xs))))
(double-and-sum-digits (rest xs)))))
(defun dmx (xs)
(if (endp (rest xs))
(mv xs nil)
(mv-let (odds evens)
(dmx (rest (rest xs)))
(mv (cons (first xs) odds)
(cons (second xs) evens)))))
(defun luhn (n)
(mv-let (odds evens)
(dmx (digits n))
(= (mod (+ (sum odds)
(sum (double-and-sum-digits evens)))
10)
0)))</lang>
- Output:
> (luhn 49927398716) T > (luhn 49927398717) NIL > (luhn 1234567812345678) NIL > (luhn 1234567812345670) T
ActionScript
<lang ActionScript>function isValid(numString:String):Boolean { var isOdd:Boolean = true; var oddSum:uint = 0; var evenSum:uint = 0; for(var i:int = numString.length - 1; i >= 0; i--) { var digit:uint = uint(numString.charAt(i)) if(isOdd) oddSum += digit; else evenSum += digit/5 + (2*digit) % 10; isOdd = !isOdd; } if((oddSum + evenSum) % 10 == 0) return true; return false; }
trace(isValid("49927398716")); trace(isValid("49927398717")); trace(isValid("1234567812345678")); trace(isValid("1234567812345670"));</lang>
Ada
<lang Ada>with Ada.Text_IO; use Ada.Text_IO;
procedure Luhn is
function Luhn_Test (Number: String) return Boolean is
Sum : Natural := 0;
Odd : Boolean := True;
Digit: Natural range 0 .. 9;
begin
for p in reverse Number'Range loop
Digit := Integer'Value (Number (p..p));
if Odd then
Sum := Sum + Digit;
else
Sum := Sum + (Digit*2 mod 10) + (Digit / 5);
end if;
Odd := not Odd;
end loop;
return (Sum mod 10) = 0;
end Luhn_Test;
begin
Put_Line (Boolean'Image (Luhn_Test ("49927398716")));
Put_Line (Boolean'Image (Luhn_Test ("49927398717")));
Put_Line (Boolean'Image (Luhn_Test ("1234567812345678")));
Put_Line (Boolean'Image (Luhn_Test ("1234567812345670")));
end Luhn;</lang>
- Output:
TRUE FALSE FALSE TRUE
ALGOL 68
<lang algol68>PROC to int = (CHAR c)INT:
ABS c - ABS "0";
PROC confirm = (STRING id)BOOL: (
BOOL is odd digit := TRUE;
INT s := 0;
STRING cp;
FOR cp key FROM UPB id BY -1 TO LWB id DO
INT k := to int(id[cp key]);
s +:=
IF is odd digit THEN k
ELIF k /= 9 THEN 2*k MOD 9
ELSE 9
FI;
is odd digit := NOT is odd digit
OD;
0 = s MOD 10
);
main: (
[]STRING t cases = (
"49927398716",
"49927398717",
"1234567812345678",
"1234567812345670"
);
FOR cp key TO UPB t cases DO
STRING cp = t cases[cp key];
print((cp, ": ", confirm(cp), new line))
OD
)</lang>
- Output:
49927398716: T 49927398717: F 1234567812345678: F 1234567812345670: T
ALGOL W
Separate source so the LuhnTest procedure can be used in other tasks, e.g.: Validate International Securities Identification Number <lang algolw>% returns true if ccNumber passes the Luhn test, false otherwise % % as Algol W has fixed length strings, the length of the number % % must be specified in ccLength % logical procedure LuhnTest ( string(32) value ccNumber
; integer value ccLength
) ;
begin
integer checkSum;
logical oddDigit, isValid;
checkSum := 0;
isValid := oddDigit := true;
for cPos := ccLength step -1 until 1 do begin
integer digit;
digit := decode( ccNumber( cPos - 1 // 1 ) ) - decode( "0" );
if digit < 0 or digit > 9 then isValid := false
else if oddDigit
then checkSum := checkSum + digit
else checkSum := checkSum + ( case digit + 1 of ( 0, 2, 4, 6, 8
, 1, 3, 5, 7, 9
)
);
oddDigit := not oddDigit
end for_cPos ;
isValid and ( ( checkSum rem 10 ) = 0 )
end LuhnTest</lang>
Use the above to test the LuhnTest procedure:
<lang algolw>begin
% external procedure that returns true if ccNumber passes the Luhn test, false otherwise %
logical procedure LuhnTest ( string(32) value ccNumber
; integer value ccLength
) ; algol "LUHN" ;
% task test cases %
procedure testLuhnTest ( string(32) value ccNumber
; integer value ccLength
) ;
write( s_w := 0, ccNumber, if LuhnTest( ccNumber, ccLength ) then " is valid" else " is invalid" );
testLuhnTest( "49927398716", 11 ); testLuhnTest( "49927398717", 11 ); testLuhnTest( "1234567812345678", 16 ); testLuhnTest( "1234567812345670", 16 )
end.</lang>
- Output:
49927398716 is valid 49927398717 is invalid 1234567812345678 is invalid 1234567812345670 is valid
APL
<lang APL>LuhnTest←{
digits←⍎¨⍵ ⍝ Characters to digits
doubled←2∘×@(⌽⍤~1 0⍴⍨≢)⊢digits ⍝ Double every other digit
partial←-∘9@(9∘<)⊢doubled ⍝ Subtract 9 is equivalent to sum of digits for the domain 10≤x≤19
0=10|+/partial ⍝ Valid if sum is a multiple of 10
}</lang>
- Output:
LuhnTest¨'49927398716' '49927398717' '1234567812345678' '1234567812345670' 1 0 0 1
<lang APL> ∇ ret←LuhnTest num;s1;s2 [1] num←⌽((⌈10⍟num)/10)⊤num [2] s1←+/((⍴num)⍴1 0)/num [3] s2←+/∊(⊂10 10)⊤¨2×((⍴num)⍴0 1)/num [4] ret←0=10⊤s1+s2
∇</lang>
- Output:
LuhnTest¨ 49927398716 49927398717 1234567812345678 1234567812345670 1 0 0 1
AppleScript
Functional
<lang applescript>-- luhn :: String -> Bool on luhn(s)
-- True if the digit string represents
-- a valid Luhn credit card number.
script divMod10Sum
on |λ|(a, x)
a + x div 10 + x mod 10
end |λ|
end script
0 = foldl(divMod10Sum, 0, ¬
zipWith(my mul, ¬
map(my int, reverse of (characters of s)), ¬
cycle({1, 2}))) mod 10
end luhn
TEST ---------------------------
on run
map(luhn, ¬
{"49927398716", "49927398717", ¬
"1234567812345678", "1234567812345670"})
--> {true, false, false, true}
end run
REUSABLE GENERIC FUNCTIONS ----------------
-- cycle :: [a] -> Generator [a] on cycle(xs)
script
property lng : 1 + (length of xs)
property i : missing value
on |λ|()
if missing value is i then
set i to 1
else
set nxt to (1 + i) mod lng
if 0 = ((1 + i) mod lng) then
set i to 1
else
set i to nxt
end if
end if
return item i of xs
end |λ|
end script
end cycle
-- foldl :: (a -> b -> a) -> a -> [b] -> a on foldl(f, startValue, xs)
tell mReturn(f)
set v to startValue
set lng to length of xs
repeat with i from 1 to lng
set v to |λ|(v, item i of xs, i, xs)
end repeat
return v
end tell
end foldl
-- int :: String -> Int on int(s)
s as integer
end int
-- length :: [a] -> Int on |length|(xs)
set c to class of xs
if list is c or string is c then
length of xs
else
(2 ^ 29 - 1) -- (maxInt - simple proxy for non-finite)
end if
end |length|
-- mReturn :: First-class m => (a -> b) -> m (a -> b) on mReturn(f)
-- 2nd class handler function lifted into 1st class script wrapper.
if script is class of f then
f
else
script
property |λ| : f
end script
end if
end mReturn
-- map :: (a -> b) -> [a] -> [b] on map(f, xs)
-- The list obtained by applying f
-- to each element of xs.
tell mReturn(f)
set lng to length of xs
set lst to {}
repeat with i from 1 to lng
set end of lst to |λ|(item i of xs, i, xs)
end repeat
return lst
end tell
end map
-- min :: Ord a => a -> a -> a on min(x, y)
if y < x then
y
else
x
end if
end min
-- mul (*) :: Num a => a -> a -> a on mul(a, b)
a * b
end mul
-- take :: Int -> [a] -> [a] -- take :: Int -> String -> String on take(n, xs)
set c to class of xs
if list is c then
if 0 < n then
items 1 thru min(n, length of xs) of xs
else
{}
end if
else if string is c then
if 0 < n then
text 1 thru min(n, length of xs) of xs
else
""
end if
else if script is c then
set ys to {}
repeat with i from 1 to n
set v to |λ|() of xs
if missing value is v then
return ys
else
set end of ys to v
end if
end repeat
return ys
else
missing value
end if
end take
-- zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] on zipWith(f, xs, ys)
set lng to min(|length|(xs), |length|(ys))
if 1 > lng then return {}
set xs_ to take(lng, xs) -- Allow for non-finite
set ys_ to take(lng, ys) -- generators like cycle etc
set lst to {}
tell mReturn(f)
repeat with i from 1 to lng
set end of lst to |λ|(item i of xs_, item i of ys_)
end repeat
return lst
end tell
end zipWith</lang>
- Output:
{true, false, false, true}
Straightforward
<lang applescript>on luhnTest(n)
-- Accept only text input.
if (n's class is not text) then return false
-- Edit out any spaces or dashes.
set astid to AppleScript's text item delimiters
set AppleScript's text item delimiters to {space, "-"}
set n to n's text items
set AppleScript's text item delimiters to ""
set n to n as text
set AppleScript's text item delimiters to astid
-- Check that what's left is numeric.
try
n as number
on error
return false
end try
-- Do the calculation two digits at a time, starting at the end of the text and working back.
set sum to 0
repeat with i from ((count n) - 1) to 1 by -2
set n2 to (text i thru (i + 1) of n) as integer
tell n2 div 10 mod 10 * 2 to set sum to sum + it div 10 + it mod 10 + n2 mod 10
end repeat
-- If there's an odd digit left over, add that in too.
if (i is 2) then set sum to sum + (character 1 of n)
return (sum mod 10 is 0)
end luhnTest
-- Test code: set testResults to {} repeat with testNumber in {"49927398716", "49927398717", "1234567812345678", "1234567812345670"}
set end of testResults to {testNumber:testNumber's contents, valid:luhnTest(testNumber)}
end repeat return testResults</lang>
- Output:
<lang applescript>{{testNumber:"49927398716", valid:true}, {testNumber:"49927398717", valid:false}, {testNumber:"1234567812345678", valid:false}, {testNumber:"1234567812345670", valid:true}}</lang>
ARM Assembly
<lang ARM_Assembly>.text .global _start _start:
ldr r0, =example_numbers bl test_number
add r1, r0, #1 bl length add r0, r1, r0 bl test_number add r1, r0, #1 bl length add r0, r1, r0 bl test_number add r1, r0, #1 bl length add r0, r1, r0 bl test_number
mov r0, #0 mov r7, #1 swi 0
test_number:
push {r0, lr}
bl print_string
bl luhn_test
cmp r0, #1
ldreq r0, =valid_message
ldrne r0, =invalid_message
bl print_string
pop {r0, lr}
mov pc, lr
print_string:
push {r0-r7, lr}
mov r1, r0 @ string to print
bl length
mov r2, r0 @ length of string
mov r0, #1 @ write to stdout
mov r7, #4 @ SYS_WRITE
swi 0 @ call system interupt
pop {r0-r7, lr}
mov pc, lr
@ r0 address of credit card number string @ returns result in r0 luhn_test:
push {r1-r7, lr}
mov r1, r0
bl isNumerical @ check if string is a number
cmp r0, #1
bne .luhn_test_end @ exit if not number
mov r0, r1
ldr r1, =reversed_string @ address to store reversed string
bl reverse @ reverse string
push {r0}
bl length @ get length of string
mov r4, r0 @ store string length in r4
pop {r0}
mov r2, #0 @ string index
mov r6, #0 @ sum of odd digits
mov r7, #0 @ sum of even digits
.loadNext:
ldrb r3, [r1, r2] @ load byte into r3
sub r3, #'0' @ convert letter to digit
and r5, r2, #1 @ test if index is even or odd
cmp r5, #0
beq .odd_digit
bne .even_digit
.odd_digit:
add r6, r3 @ add digit to sum if odd
b .continue @ skip next step
.even_digit:
lsl r3, #1 @ multiply digit by 2
cmp r3, #10 @ sum digits
subge r3, #10 @ get digit in 1s place
addge r3, #1 @ add 1 for the 10s place
add r7, r3 @ add digit sum to the total
.continue:
add r2, #1 @ increment digit index
cmp r2, r4 @ check if at end of string
blt .loadNext
add r0, r6, r7 @ add even and odd sum
mov r3, r0 @ copy sum to r3
ldr r1, =429496730 @ (2^32-1)/10
sub r0, r0, r0, lsr #30 @ divide by 10
umull r2, r0, r1, r0
mov r1, #10
mul r0, r1 @ multiply the r0 by 10 to see if divisible
cmp r0, r3 @ compare with the original value in r3
.luhn_test_end:
movne r0, #0 @ return false if invalid card number
moveq r0, #1 @ return true if valid card number
pop {r1-r7, lr}
mov pc, lr
length:
push {r1-r2, lr}
mov r2, r0 @ start of string address
.loop:
ldrb r1, [r2], #1 @ load byte from address r2 and increment
cmp r1, #0 @ check for end of string
bne .loop @ load next byte if not 0
sub r0, r2, r0 @ subtract end of string address from start
sub r0, #1 @ end of line from count
pop {r1-r2, lr}
mov pc, lr
@ reverses a string @ r0 address of string to reverse @ r1 address to store reversed string reverse:
push {r0-r5, lr}
push {r0, lr}
bl length @ get length of string to reverse
mov r3, r0 @ backword index
pop {r0, lr}
mov r4, #0 @ fowrard index
.reverse_next:
sub r3, #1 @ decrement backword index
ldrb r5, [r0, r3] @ load byte from original string at index
strb r5, [r1, r4] @ copy byte to reversed string
add r4, #1 @ increment fowrard index
cmp r3, #0 @ check if any characters are left
bge .reverse_next
mov r5, #0
strb r5, [r1, r4] @ write null byte to terminate reversed string
pop {r0-r5, lr}
mov pc, lr
isNumerical:
push {r1, lr}
.isNumerical_checkNext:
ldrb r1, [r0], #1
cmp r1, #0
beq .isNumerical_true
cmp r1, #'0'
blt .isNumerical_false
cmp r1, #'9'
bgt .isNumerical_false
b .isNumerical_checkNext
.isNumerical_false:
mov r0, #0
b .isNumerical_end
.isNumerical_true:
mov r0, #1
.isNumerical_end:
pop {r1, lr}
mov pc, lr
.data
valid_message:
.asciz " valid card number\n"
invalid_message:
.asciz " invalid card number\n"
reversed_string:
.space 32
example_numbers:
.asciz "49927398716" .asciz "49927398717" .asciz "1234567812345678" .asciz "1234567812345670" </lang>
AutoHotkey
<lang AutoHotkey>; Originally submitted by Laszlo:
MsgBox % LuhnTest(49927398716) MsgBox % LuhnTest(49927398717) MsgBox % LuhnTest(1234567812345678) MsgBox % LuhnTest(1234567812345670)
Return
- -----------------------------
LuhnTest(Number) {
MultFactor := 2 - ( StrLen(Number) & 1 ) , Sum := 0 Loop, Parse, Number Sum += ( ( 9 < ( Temp := MultFactor * A_LoopField ) ) ? Temp - 9 : Temp ) , MultFactor := 3 - MultFactor Return !Mod(Sum,10)
}</lang>
AutoIt
<lang AutoIt> Global $avarray[4] = [49927398716, 49927398717, 1234567812345678, 1234567812345670] For $i = 0 To 3 checkLuhn($avarray[$i]) Next
Func checkLuhn($number) $sum = 0 $numDigits = StringSplit($number, "") For $i = $numDigits[0] - 1 To 1 Step -2 $numDigits[$i] = $numDigits[$i] * 2 If $numDigits[$i] >= 10 Then $numDigits[$i] -= 9 Next For $i = 1 To $numDigits[0] $sum += $numDigits[$i] Next If StringRight($sum, 1) = "0" Then ConsoleWrite("Luhn-Check (" & $number & ") : True" & @CRLF) Return True Else ConsoleWrite("Luhn-Check (" & $number & ") : False" & @CRLF) Return False EndIf EndFunc ;==>checkLuhn </lang>
- Output:
Luhn-Check (49927398716) : True Luhn-Check (49927398717) : False Luhn-Check (1234567812345678) : False Luhn-Check (1234567812345670) : True
AWK
<lang awk>#!/usr/bin/awk -f BEGIN {
A[1] = 49927398716;
A[2] = 49927398717;
A[3] = 1234567812345678;
A[4] = 1234567812345670;
A[5] = "01234567897";
A[6] = "01234567890";
A[7] = "00000000000";
for (k in A) print "isLuhn("A[k]"): ",isLuhn(A[k]);
}
function isLuhn(cardno) {
s = 0;
m = "0246813579";
n = length(cardno);
for (k = n; 0 < k; k -= 2) {
s += substr(cardno, k, 1);
}
for (k = n-1; 0 < k; k -= 2) {
s += substr(m, substr(cardno, k, 1)+1, 1);
} return ((s%10)==0);
}</lang>
- Output:
isLuhn(1234567812345670): 1 isLuhn(01234567897): 1 isLuhn(01234567890): 0 isLuhn(00000000000): 1 isLuhn(49927398716): 1 isLuhn(49927398717): 0 isLuhn(1234567812345678): 0
Bash
<lang bash>#!/bin/bash
function luhn_validate # <numeric-string> {
num=$1 shift 1
len=${#num}
is_odd=1
sum=0
for((t = len - 1; t >= 0; --t)) {
digit=${num:$t:1}
if $is_odd -eq 1 ; then sum=$(( sum + $digit )) else sum=$(( $sum + ( $digit != 9 ? ( ( 2 * $digit ) % 9 ) : 9 ) )) fi
is_odd=$(( ! $is_odd )) }
# NOTE: returning exit status of 0 on success return $(( 0 != ( $sum % 10 ) ))
}
function print_result # <numeric-string>
{
if luhn_validate "$1"; then
echo "$1 is valid"
else
echo "$1 is not valid"
fi
}
print_result "49927398716" print_result "49927398717" print_result "1234567812345678" print_result "1234567812345670"</lang>
- Output:
49927398716 is valid 49927398717 is not valid 1234567812345678 is not valid 1234567812345670 is valid
Batch File
This simple implementation does not reverse the numbers. Instead, it counts from right to left. <lang dos>@echo off setlocal enabledelayedexpansion
call :luhn 49927398716 call :luhn 49927398717 call :luhn 1234567812345678 call :luhn 1234567812345670 exit /b 0
- luhn
set input=%1 set cnt=0 set s1=0&set s2=0
- digit_loop
set /a cnt-=1 set /a isOdd=^(-%cnt%^)%%2
if !isodd! equ 1 ( set /a s1+=!input:~%cnt%,1! ) else ( set /a twice=!input:~%cnt%,1!*2 if !twice! geq 10 ( set /a s2+=!twice:~0,1!+!twice:~1,1! ) else ( set /a s2+=!twice! ) ) if "!input:~%cnt%!"=="!input!" ( set /a sum=^(!s1!+!s2!^)%%10 if !sum! equ 0 (echo !input! is valid.) else (echo !input! is not valid.) goto :EOF ) goto digit_loop</lang>
- Output:
>luhn.bat 49927398716 is valid. 49927398717 is not valid. 1234567812345678 is not valid. 1234567812345670 is valid. >
BBC BASIC
<lang bbcbasic> FOR card% = 1 TO 4
READ cardnumber$
IF FNluhn(cardnumber$) THEN
PRINT "Card number " cardnumber$ " is valid"
ELSE
PRINT "Card number " cardnumber$ " is invalid"
ENDIF
NEXT card%
END
DATA 49927398716, 49927398717, 1234567812345678, 1234567812345670
DEF FNluhn(card$)
LOCAL I%, L%, N%, S%
L% = LEN(card$)
FOR I% = 1 TO L%
N% = VAL(MID$(card$, L%-I%+1, 1))
IF I% AND 1 THEN
S% += N%
ELSE
N% *= 2
S% += N% MOD 10 + N% DIV 10
ENDIF
NEXT
= (S% MOD 10) = 0</lang>
bc
<lang bc>/* Return 1 if number passes Luhn test, else 0 */ define l(n) {
auto m, o, s, x
o = scale scale = 0
m = 1
while (n > 0) {
x = (n % 10) * m
if (x > 9) x -= 9
s += x
m = 3 - m
n /= 10
}
s %= 10 scale = o if (s) return(0) return(1)
}
l(49927398716) l(49927398717) l(1234567812345678) l(1234567812345670)</lang>
- Output:
1 0 0 1
Befunge
<lang befunge>v 1 >$0 v v < >&:19+`|v < >v 5 6 7 8 ^ \ <>09p19p>09g+09p:|>2*:19+%19g+19p19+/19g+19p:|
2 3 4 > v
v"invalid"<10 9
|%+91+g91g90<
v "valid"<
>:#,_@
11
</lang> The labelled points (1 to 11) are: 1. Read in input until number greater than 10, 2. Reverse the order, 3. Set accumulators to 0, 4. Add odd number to accumulator, 5. Mod even number with 10, 6. Add this digit to accumulator, 7. Integer divide number by 10, 8. Add this digit to accumulator, 9. Add odd and even accumulators, 10. Mod this accumulator with 10, 11. Print result.
The code requires input be separated by spaces and ended with a number greater than 10 to exit the reading loop. This could be done by reading characters and ending at a new line, but this way is much simpler.
Inputs:
4 9 9 2 7 3 9 8 7 1 6 99 4 9 9 2 7 3 9 8 7 1 7 99 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 99 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 0 99
- Output:
valid invalid invalid valid
Bracmat
<lang bracmat> ( luhn
= sum odd even
. 0:?sum
& rev$!arg:?arg
& whl
' ( @( !arg
: %?odd
( %?even ?arg
| :?arg&0:?even
)
)
& !odd+mod$(2*!even.10)+div$(!even.5)+!sum:?sum
)
& mod$(!sum.10):0
)
& ( test
=
. out
$ (!arg ":" (luhn$!arg&true|false))
)
& test$49927398716 & test$49927398717 & test$1234567812345678 & test$1234567812345670 & ;</lang>
- Output:
49927398716 : true 49927398717 : false 1234567812345678 : false 1234567812345670 : true
Brainf***
<lang>>>>>>>>>>+>,----------[ READ CHARACTERS UNTIL \N AND
>++++++++[<----->-]<++>>>>>>+>,----------] SUBTRACT ASCII 0 FROM EACH
<-<<<<<<< GO TO LAST DIGIT [ WHILE THERE ARE DIGITS
>>>>>>>>[-<<<<<<<+>>>>>>>]<<<<<<<< ADD RUNNING TOTAL TO ODD DGT
<<<<<<< GO TO EVEN DIGIT
[ IF THERE IS ONE
>[->++<]>[-<+>] MUL BY TWO
>>>++++++++++<<<<[ DIVMOD BY TEN
>>>[-]+>-[<-<]<[<<] DECR DIVISOR
>>[ IF ZERO
>++++++++++>+<<-]<<< SET TO TEN; INCR QUOTIENT
-] DECR DIVIDEND UNTIL ZERO
++++++++++>>>>[-<<<<->>>>] CALCULATE REMAINDER
>[-<<<<<+>>>>>] ADD QUOTIENT TO IT
>>[-<<<<<<<+>>>>>>>]<<<<<<<< THEN ADD RUNNING TOTAL
<<<<< ZERO BEFORE NEXT ODD DIGIT
]<< GO TO NEXT ODD DIGIT
] >>>>>>>-[+>>-]> GO TO TOTAL >>>>++++++++++<<<<[ MODULO TEN
>>>[-]+>-[<-<]<[<<] DECR DIVISOR >>[>++++++++++<-] IF ZERO SET BACK TO TEN
<<<-] DECR DIVIDEND UNTIL ZERO >>>++++++++++>[-<->]< REMAINDER: TEN MINUS DIVISOR <<<<<<++++++++++[-> VALUES FOR ASCII OUTPUT
+++++++++++> 110 ++++++++++> 100 ++++++++> 80 +++++++<<<<] 70
>>>>>+> GO BACK TO REMAINDER [<<.<<---.<-----.+++.<] IF NOT ZERO FAIL <[<<.<---.<+++++..<] IF ZERO PASS ++++++++++. NEWLINE </lang>
- Output:
$ echo 49927398716 | beef luhn.bf Pass $ echo 49927398717 | beef luhn.bf Fail $ echo 1234567812345678 | beef luhn.bf Fail $ echo 1234567812345670 | beef luhn.bf Pass
C
<lang c>#include <string.h>
- include <stdio.h>
int luhn(const char* cc) { const int m[] = {0,2,4,6,8,1,3,5,7,9}; // mapping for rule 3 int i, odd = 1, sum = 0;
for (i = strlen(cc); i--; odd = !odd) { int digit = cc[i] - '0'; sum += odd ? digit : m[digit]; }
return sum % 10 == 0; }
int main() { const char* cc[] = { "49927398716", "49927398717", "1234567812345678", "1234567812345670", 0 }; int i;
for (i = 0; cc[i]; i++) printf("%16s\t%s\n", cc[i], luhn(cc[i]) ? "ok" : "not ok");
return 0;
}</lang>
- Output:
49927398716 ok
49927398717 not ok
1234567812345678 not ok
1234567812345670 ok
C#
The LuhnCheck method takes an array of integers because values in memory will be integer-aligned.
<lang csharp>
public static class Luhn
{
public static bool LuhnCheck(this string cardNumber)
{
return LuhnCheck(cardNumber.Select(c => c - '0').ToArray());
}
private static bool LuhnCheck(this int[] digits)
{
return GetCheckValue(digits) == 0;
}
private static int GetCheckValue(int[] digits)
{
return digits.Select((d, i) => i % 2 == digits.Length % 2 ? ((2 * d) % 10) + d / 5 : d).Sum() % 10;
}
}
public static class TestProgram
{
public static void Main()
{
long[] testNumbers = {49927398716, 49927398717, 1234567812345678, 1234567812345670};
foreach (var testNumber in testNumbers)
Console.WriteLine("{0} is {1}valid", testNumber, testNumber.ToString().LuhnCheck() ? "" : "not ");
}
}
</lang>
49927398716 is valid 49927398717 is not valid 1234567812345678 is not valid 1234567812345670 is valid
Note that the original implementation, which follows, is flawed because it assumes that n is a number which, when represented as a string, has an even number of characters. Granted, the brief is for Credit Card Numbers which are all, at the time of writing, an even number of digits.
<lang csharp>using System; using System.Linq;
namespace Luhn {
class Program
{
public static bool luhn(long n)
{
long nextdigit, sum = 0;
bool alt = false;
while (n != 0)
{
nextdigit = n % 10;
if (alt)
{
nextdigit *= 2;
nextdigit -= (nextdigit > 9) ? 9 : 0;
}
sum += nextdigit;
alt = !alt;
n /= 10;
}
return (sum % 10 == 0);
}
public static bool luhnLinq(long n)
{
string s = n.ToString();
return s.Select((c, i) => (c - '0') << ((s.Length - i - 1) & 1)).Sum(n => n > 9 ? n - 9 : n) % 10 == 0;
}
static void Main(string[] args)
{
long[] given = new long[] {49927398716, 49927398717, 1234567812345678, 1234567812345670};
foreach (long num in given)
{
string valid = (luhn(num)) ? " is valid" : " is not valid";
Console.WriteLine(num + valid);
}
}
}
}</lang>
49927398716 is valid 49927398717 is not valid 1234567812345678 is not valid 1234567812345670 is valid
A solution without using LINQ, works for all versions of .NET. <lang csharp> using System; namespace Luhn_Test { public static class Extensions { public static string Reverse(this string s ) { char[] charArray = s.ToCharArray(); Array.Reverse( charArray ); return new string( charArray ); } } class Program { public static bool Luhn(long x) { long s1=0; long s2=0; bool STATE=x%10!=0; // If it ends with zero, we want the order to be the other way around x=long.Parse(x.ToString().Reverse()); while (x!=0) { s1+=STATE?x%10:0; s2+=STATE?0:((x%10)*2>9)?(((x%10)*2/10)+((x%10)*2)%10):((x%10)*2); STATE=!STATE; //Switch state x/=10; //Cut the last digit and continue } return ((s1+s2)%10==0); //Check if it ends with zero, if so, return true, otherwise,false. } public static void Main(string[] args) { long[] ks = {1234567812345670, 49927398717, 1234567812345678 ,1234567812345670 }; foreach (long k in ks) { Console.WriteLine("{0} is {1} Valid.",k,Luhn(k)?"":"Not"); } Start: try { Console.WriteLine("Enter your credit:"); long x=long.Parse(Console.ReadLine()); Console.WriteLine("{0} Valid.",Luhn(x)?"":"Not"); goto Start; } catch (FormatException) { goto Start; } } } } </lang>
1234567812345670 is Valid. 49927398717 is Not Valid. 1234567812345678 is Not Valid. 49927398716 is Valid.
A solution optimized for readability: <lang csharp> using System; using System.Linq;
public class CreditCardLogic {
static Func<char, int> charToInt = c => c - '0';
static Func<int, int> doubleDigit = n => (n * 2).ToString().Select(charToInt).Sum();
static Func<int, bool> isOddIndex = index => index % 2 == 0;
public static bool LuhnCheck(string creditCardNumber)
{
var checkSum = creditCardNumber
.Select(charToInt)
.Reverse()
.Select((digit, index) => isOddIndex(index) ? digit : doubleDigit(digit))
.Sum();
return checkSum % 10 == 0; }
} </lang>
Extremely compact version uses Europa rtl library https://github.com/CodeAlkemist/Europa-rtl <lang csharp> using System; using EuropaRTL.Utilities;
public static partial class Algoritmhs {
public static bool CheckLuhn(long n)
{
int s1 = n.Shatter(true).Subset(2).Arithmetic('+');
int s2 = n.Shatter(true).Subset(1, -1, 2).ArithmeticRA('*', 2).ShatterAndSum().Arithmetic('+');
return (s1 + s2) % 10 == 0 ? true : false;
}
} class Program {
static void Main(string[] args)
{
long[] ll = {
49927398716,
49927398717,
1234567812345678,
1234567812345670
};
foreach (var item in ll)
{
item.ToString().WriteLine();
Algoritmhs.CheckLuhn(item).ToString().WriteLine();
}
Console.ReadKey();
}
} </lang>
49927398716 True 49927398717 False 1234567812345678 False 1234567812345670 False
C++
<lang cpp>#include <iostream> using namespace std;
int toInt(const char c) {
return c-'0';
}
int confirm( const char *id) {
bool is_odd_dgt = true; int s = 0; const char *cp;
for(cp=id; *cp; cp++);
while(cp > id) {
--cp;
int k = toInt(*cp);
if (is_odd_dgt) {
s += k;
}
else {
s += (k!=9)? (2*k)%9 : 9;
}
is_odd_dgt = !is_odd_dgt;
} return 0 == s%10;
}
int main( ) {
const char * t_cases[] = {
"49927398716",
"49927398717",
"1234567812345678",
"1234567812345670",
NULL,
};
for ( const char **cp = t_cases; *cp; cp++) {
cout << *cp << ": " << confirm(*cp) << endl;
}
return 0;
}</lang>
C++11
<lang cpp>#include <iostream>
- include <vector>
- include <algorithm>
using namespace std;
bool luhn( const string& id) {
static const int m[10] = {0,2,4,6,8,1,3,5,7,9}; // mapping for rule 3
bool is_odd_dgt = false;
auto lambda = [&](int a, char c) {return a + ((is_odd_dgt = !is_odd_dgt) ? c-'0' : m[c-'0']);};
int s = std::accumulate(id.rbegin(), id.rend(), 0, lambda);
return 0 == s%10;
}
int main( ) {
auto t_cases = {"49927398716", "49927398717", "1234567812345678", "1234567812345670"};
auto print = [](const string & s) {cout << s << ": " << luhn(s) << endl;};
for_each(t_cases.begin(), t_cases.end(), print);
return 0;
} </lang>
It is also possible to achieve a compile-time version using metaprogramming.
<lang cpp>#include <iostream>
- include <type_traits>
template<size_t I, int... Args> struct find_impl;
template<int A, int... Args> struct find_impl<0, A, Args...> {
using type = std::integral_constant<int, A>;
};
template<int A, int B, int... Args> struct find_impl<0, A, B, Args...> {
using type = std::integral_constant<int, A>;
};
template<size_t I, int A, int B, int... Args> struct find_impl<I, A, B, Args...> {
using type = typename find_impl<I-1, B, Args...>::type;
};
namespace detail { template<typename, typename> struct append_sequence {};
template<typename T, typename... Ts> struct append_sequence<T, std::tuple<Ts...>> {
using type = std::tuple<Ts..., T>;
};
template<typename... Ts> struct reverse_sequence {
using type = std::tuple<>;
};
template<typename T, typename... Ts> struct reverse_sequence<T, Ts...> {
using type = typename append_sequence<
T,
typename reverse_sequence<Ts...>::type
>::type;
}; }
template<size_t I> using rule3 = typename find_impl<I, 0, 2, 4, 6, 8, 1, 3, 5, 7, 9>::type;
template<int A, char C, bool dgt> struct calc
: std::integral_constant<int, A + C - '0'>
{};
template<int A, char C> struct calc<A, C, false>
: std::integral_constant<int, A + rule3<C - '0'>::type::value>
{};
template<typename Acc, bool Dgt, char...> struct luhn_impl;
template<typename Acc, bool Dgt, char A, char... Args> struct luhn_impl<Acc, Dgt, A, Args...> {
using type = typename calc<Acc::value, A, Dgt>::type;
};
template<typename Acc, bool Dgt, char A, char B, char... Args> struct luhn_impl<Acc, Dgt, A, B, Args...> {
using type =
typename luhn_impl<typename calc<Acc::value, A, Dgt>::type, !Dgt, B, Args...>::type;
};
template<typename> struct luhn;
template<typename... Args> struct luhn<std::tuple<Args...>> {
using type = typename luhn_impl<std::integral_constant<int, 0>, true, Args::value...>::type; constexpr static bool result = (type::value % 10) == 0;
};
template<char... Args> bool operator "" _luhn() {
return luhn<typename detail::reverse_sequence<std::integral_constant<char, Args>...>::type>::result;
}
int main() {
std::cout << std::boolalpha; std::cout << 49927398716_luhn << std::endl; std::cout << 49927398717_luhn << std::endl; std::cout << 1234567812345678_luhn << std::endl; std::cout << 1234567812345670_luhn << std::endl; return 0;
} </lang>
true false false true
Caché ObjectScript
<lang cos>Class Utils.Check [ Abstract ] {
ClassMethod Luhn(x As %String) As %Boolean { // https://www.simple-talk.com/sql/t-sql-programming/calculating-and-verifying-check-digits-in-t-sql/ SET x=$TRANSLATE(x," "), cd=$EXTRACT(x,*) SET x=$REVERSE($EXTRACT(x,1,*-1)), t=0 FOR i=1:1:$LENGTH(x) { SET n=$EXTRACT(x,i) IF i#2 SET n=n*2 IF $LENGTH(n)>1 SET n=$EXTRACT(n,1)+$EXTRACT(n,2) SET t=t+n } QUIT cd=((t*9)#10) }
}</lang>
- Examples:
USER>For { Read ccn Quit:ccn="" Write ": "_##class(Utils.Check).Luhn(ccn), ! }
49927398716: 1
49927398717: 0
1234567812345678: 0
1234567812345670: 1
USER>
Ceylon
<lang ceylon>shared void run() { value numbers = "49927398716 49927398717 1234567812345678 1234567812345670"; for(number in numbers.lines) { print("``number`` passes? ``luhn(number)``"); } }
shared Boolean luhn(String number) { value digits = number .reversed .map(Character.string) .map(Integer.parse) .narrow<Integer>(); value s1 = sum { 0, *digits.by(2) }; value s2 = sum { 0, *digits .skip(1) .by(2) .map(curry(times<Integer>)(2)) .map((Integer element) => element / 10 + element % 10) }; return (s1 + s2) % 10 == 0; }</lang>
Clojure
<lang clojure>(defn luhn? [cc]
(let [factors (cycle [1 2])
numbers (map #(Character/digit % 10) cc)
sum (reduce + (map #(+ (quot % 10) (mod % 10))
(map * (reverse numbers) factors)))]
(zero? (mod sum 10))))
(doseq [n ["49927398716" "49927398717" "1234567812345678" "1234567812345670"]]
(println (luhn? n)))</lang>
COBOL
<lang cobol> IDENTIFICATION DIVISION.
PROGRAM-ID. LUHNTEST.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
data division.
WORKING-STORAGE SECTION.
01 inp-card.
03 inp-card-ch pic x(01) occurs 20 times.
01 ws-result pic 9(01).
88 pass-luhn-test value 0.
PROCEDURE DIVISION.
move "49927398716" to inp-card
perform test-card
move "49927398717" to inp-card
perform test-card
move "1234567812345678" to inp-card
perform test-card
move "1234567812345670" to inp-card
perform test-card
stop run
.
test-card.
call "LUHN" using inp-card, ws-result
if pass-luhn-test
display "input=" inp-card "pass"
else
display "input=" inp-card "fail"
.
END PROGRAM LUHNTEST.
IDENTIFICATION DIVISION.
PROGRAM-ID. LUHN.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 maxlen pic 9(02) comp value 16.
01 inplen pic 9(02) comp value 0.
01 i pic 9(02) comp value 0.
01 j pic 9(02) comp value 0.
01 l pic 9(02) comp value 0.
01 dw pic 9(02) comp value 0.
01 ws-total pic 9(03) comp value 0.
01 ws-prod pic 99.
01 filler redefines ws-prod.
03 ws-prod-tens pic 9.
03 ws-prod-units pic 9.
01 ws-card.
03 filler occurs 16 times depending on maxlen.
05 ws-card-ch pic x(01).
05 ws-card-digit redefines ws-card-ch pic 9(01).
LINKAGE SECTION.
01 inp-card.
03 inp-card-ch pic x(01) occurs 20 times.
01 ws-result pic 9(01).
88 pass-luhn-test value 0.
PROCEDURE DIVISION using inp-card, ws-result.
perform varying i from 1 by +1
until i > maxlen
or inp-card-ch (i) = space
end-perform
compute l = i - 1
compute inplen = l
perform varying j from 1 by +1
until j > inplen
if l < 1
move "0" to ws-card-ch (j)
else
move inp-card-ch (l) to ws-card-ch (j)
compute l = l - 1
end-if
end-perform
move 0 to ws-total
perform varying i from 1 by +1
until i > inplen
compute dw = 2 - (i - 2 * function integer (i / 2))
compute ws-prod = ws-card-digit (i) * dw
compute ws-total = ws-total
+ ws-prod-tens
+ ws-prod-units
end-perform
compute ws-result = ws-total - 10 * function integer (ws-total / 10)
goback
.
END PROGRAM LUHN.</lang>
- Output:
input=49927398716 pass input=49927398717 fail input=1234567812345678 fail input=1234567812345670 pass
Common Lisp
<lang lisp>(defun luhn (n)
(labels ((sum-digits (n) (if (> n 9) (- n 9) n)))
(let ((n* (reverse n)) (l (length n)))
(let ((s1 (loop for i from 0 below l by 2
summing (digit-char-p (aref n* i)))) (s2 (loop for i from 1 below l by 2 summing (sum-digits (* 2 (digit-char-p (aref n* i))))))) (zerop (mod (+ s1 s2) 10))))))</lang> Another version, using Maciej Pasternacki's reader macros for function composition and currying in the curly package: <lang lisp>(require :curly) (use-package :curly) (enable-curly-syntax)
(defun luhn (seq)
(labels ((sum-digits (n) (if (> n 9) (- n 9) n)))
(funcall {zerop (mod * 10) (apply #'+) (mapcar #'sum-digits)
(mapcar #'* '#1=(1 2 . #1#)) (map 'list #'digit-char-p) reverse} seq)))</lang>
Cowgol
<lang cowgol>include "cowgol.coh";
- Given a string containing the digits of a credit card number,
- see if it passes the Luhn test.
sub luhn(card: [uint8]): (ok: uint8) is
# Scan ahead to last digit, counting digits
var n: uint8 := 0;
while [card] != 0 loop
n := n + 1;
card := @next card;
end loop;
var sum: uint8 := 0;
while n > 0 loop
# odd digit is simply added
card := @prev card;
n := n - 1;
sum := sum + ([card] - '0');
# if uneven amount of digits, stop
if n == 0 then break; end if;
# even digit
card := @prev card;
n := n - 1;
var digit := [card] - '0';
# it is good to avoid unnecessary multiplication/
# division, since 8-bit processors and microcontrollers
# don't tend to have that in hardware
if digit < 5 then
sum := sum + digit + digit;
else
digit := digit - 5;
sum := sum + digit + digit + 1;
end if;
end loop;
# there is no boolean type, comparisons only work
# in conditionals; this is the only way to return
# a status
if sum % 10 == 0 then
ok := 1;
else
ok := 0;
end if;
end sub;
- Test and print
sub test(card: [uint8]) is
var msg: [uint8][] := {"Fail", "Pass"};
print(card);
print(": ");
print(msg[luhn(card)]);
print_nl();
end sub;
test("49927398716"); test("49927398717"); test("1234567812345678"); test("1234567812345670");</lang>
- Output:
49927398716: Pass 49927398717: Fail 1234567812345678: Fail 1234567812345670: Pass
Crystal
<lang ruby>def luhn_valid?(n) # Card values can be numbers or strings
d2sum = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9] sum, n = 0, n.to_u64 while n > 0; sum += n%10; n //= 10; sum += d2sum[n%10]; n //= 10 end sum % 10 == 0
end
cards = [49927398716, "49927398717", 1234567812345678, "1234567812345670"] cards.each{ |i| puts "#{i}: #{luhn_valid?(i)}" }</lang>
- Output:
49927398716: true 49927398717: false 1234567812345678: false 1234567812345670: true
D
Functional Version
<lang d>import std.algorithm, std.range, std.string;
enum luhnTest = (in string n) pure /*nothrow*/ @safe /*@nogc*/ =>
retro(n) .zip(only(1, 2).cycle) .map!(p => (p[0] - '0') * p[1]) .map!(d => d / 10 + d % 10) .sum % 10 == 0;
void main() {
assert("49927398716 49927398717 1234567812345678 1234567812345670"
.split.map!luhnTest.equal([true, false, false, true]));
}</lang>
More Imperative Version
<lang d>import std.algorithm;
bool luhnTest(in string num) @safe pure nothrow @nogc {
uint sum;
foreach_reverse (immutable i, immutable n; num) {
immutable uint ord = n - '\u0030';
sum += ((num.length - i) & 1) ? ord : ord / 5 + (2 * ord) % 10;
}
return sum % 10 == 0;
}
void main() {
immutable data = ["49927398716",
"49927398717",
"1234567812345678",
"1234567812345670"];
assert(data.map!luhnTest.equal([true, false, false, true]));
}</lang>
Stronger Statically Typed Version
This version uses more precise types.
<lang d>import std.stdio;
struct Interval(T) {
immutable T a, b;
this(in T a_, in T b_) pure nothrow @nogc {
this.a = a_;
this.b = b_;
}
bool opBinaryRight(string op="in")(in T x)
const pure nothrow @nogc {
return x >= a && x <= b;
}
pure nothrow @safe @nogc const invariant {
assert(a <= b);
}
}
Interval!T interval(T)(in T a, in T b) pure nothrow @nogc {
return Interval!T(a, b);
}
bool luhnTest(in string num) pure nothrow @nogc
in {
assert(num.length <= 20);
} body {
int sum = 0; bool od = true; bool ok = true; immutable int numLen = num.length;
foreach_reverse (immutable p; 0 .. numLen) {
immutable int i = num[p] - '0';
if (i !in interval(0, 9)) {
ok = false;
break;
}
immutable int x = ((i * 2) % 10) + (i / 5);
assert((numLen - p) in interval(0, 19));
assert(sum in interval(0, (numLen - p) * 10));
assert(i in interval(0, 9));
assert(x in interval(0, 9));
sum += od ? i : x;
od = !od;
}
return ok && (sum % 10) == 0;
}
void main() {
foreach (immutable n; ["49927398716", "49927398717",
"1234567812345678", "1234567812345670",
"123456781234567D"])
writefln("%s is %svalid", n, luhnTest(n) ? "" : "not ");
}</lang>
EchoLisp
<lang lisp>
- value for 'even' numbers
(define (even-val n) (if (> n 4) (+ n n -9) (+ n n)))
- Luhn test
- input
- a string of decimal digits
- output #t or #f
(define (valid nums (odd #f ))
(let ((nums (map string->number (reverse (string->list nums)))))
(= 0 (modulo
(for/sum ((n nums)) (set! odd (not odd)) (if odd n (even-val n)))
10))))
(valid "49927398716") → #t (valid "1234567812345670") → #t (valid "1234567812345678") → #f (valid "49927398717") → #f </lang>
Elixir
<lang elixir>defmodule Luhn do
def valid?(cc) when is_binary(cc), do: String.to_integer(cc) |> valid?
def valid?(cc) when is_integer(cc) do
0 == Integer.digits(cc)
|> Enum.reverse
|> Enum.chunk(2, 2, [0])
|> Enum.reduce(0, fn([odd, even], sum) -> Enum.sum([sum, odd | Integer.digits(even*2)]) end)
|> rem(10)
end
end
numbers = ~w(49927398716 49927398717 1234567812345678 1234567812345670) for n <- numbers, do: IO.puts "#{n}: #{Luhn.valid?(n)}"</lang>
- Output:
49927398716: true 49927398717: false 1234567812345678: false 1234567812345670: true
Emacs Lisp
<lang lisp> (require 'seq) (defun luhn (str)
"Check if an input string STR is valid using lhun algorithm."
(if (string-match-p "[^0-9]" str)
(error "String contains invalid character")
(progn
(let ((digit-list (reverse (mapcar #'(lambda (x) (- x 48))
(string-to-list str)))))
(zerop
(mod (apply #'+ (seq-map-indexed
(lambda (elt idx)
(if (oddp idx)
(if (> (* 2 elt) 9)
(- (* 2 elt) 9)
(* 2 elt))
elt))
digit-list))
10))))))
(mapcar #'luhn '("49927398716" "49927398717" "1234567812345678" "1234567812345670"))
</lang>
- Output:
(t nil nil t)
Erlang
<lang Erlang> -module(luhn_test).
-export( [credit_card/1, task/0] ).
luhn_sum([Odd, Even |Rest]) when Even >= 5 ->
Odd + 2 * Even - 10 + 1 + luhn_sum(Rest);
luhn_sum([Odd, Even |Rest]) ->
Odd + 2 * Even + luhn_sum(Rest);
luhn_sum([Odd]) ->
Odd;
luhn_sum([]) ->
0.
check( Sum ) when (Sum rem 10) =:= 0 -> valid; check( _Sum ) -> invalid.
credit_card(Digits) ->
check(luhn_sum(lists:map(fun(D) -> D-$0 end, lists:reverse(Digits)))).
task() ->
Numbers = ["49927398716", "49927398717", "1234567812345678", "1234567812345670"],
[io:fwrite("~s: ~p~n", [X, credit_card(X)]) || X <- Numbers].
</lang>
- Output:
16> luhn_test:task(). 49927398716: valid 49927398717: invalid 1234567812345678: invalid 1234567812345670: valid
Euphoria
<lang euphoria>function luhn(sequence cc)
integer isOdd, oddSum, evenSum, digit
isOdd = 1
oddSum = 0
evenSum = 0
for i = length(cc) to 1 by -1 do
digit = cc[i] - '0'
if isOdd then
oddSum += digit
else
evenSum += floor(digit / 5) + remainder(2 * digit, 10)
end if
isOdd = not isOdd
end for
return not remainder(oddSum + evenSum, 10)
end function
constant cc_numbers = {
"49927398716", "49927398717", "1234567812345678", "1234567812345670"
}
for i = 1 to length(cc_numbers) do
printf(1,"%s = %d\n", {cc_numbers[i], luhn(cc_numbers[i])})
end for</lang>
- Output:
49927398716 = 1 49927398717 = 0 1234567812345678 = 0 1234567812345670 = 1
F#
<lang fsharp>let luhn (s:string) =
let rec g r c = function
| 0 -> r
| i ->
let d = ((int s.[i - 1]) - 48) <<< c
g (r + if d < 10 then d else d - 9) (1 - c) (i - 1)
(g 0 0 s.Length) % 10 = 0</lang>
Factor
<lang factor>USING: kernel math math.parser math.order math.ranges sequences ; IN: luhn
- reversed-digits ( n -- list )
{ } swap
[ dup 0 > ]
[ 10 /mod swapd suffix swap ]
while drop ;
- luhn-digit ( n -- n )
reversed-digits dup length <iota> [
2dup swap nth
swap odd? [ 2 * 10 /mod + ] when
] map sum 10 mod
nip ;
- luhn? ( n -- ? )
luhn-digit 0 = ;
</lang>
- Output:
( scratchpad ) 49927398716 luhn? . t ( scratchpad ) 49927398717 luhn? . f ( scratchpad ) 1234567812345678 luhn? . f ( scratchpad ) 1234567812345670 luhn? . t
Forth
<lang forth>: luhn ( addr len -- ? )
0 >r over + ( R: sum )
begin 1- 2dup <=
while \ odd
dup c@ [char] 0 -
r> + >r
1- 2dup <=
while \ even
dup c@ [char] 0 -
2* 10 /mod + \ even digits doubled, split, and summed
r> + >r
repeat then
2drop r> 10 mod 0= ;
s" 49927398716" luhn . \ -1 s" 49927398717" luhn . \ 0 s" 1234567812345678" luhn . \ 0 s" 1234567812345670" luhn . \ -1</lang>
Fortran
<lang fortran>program luhn
implicit none integer :: nargs character(len=20) :: arg integer :: alen, i, dr integer, allocatable :: number(:) integer, parameter :: drmap(0:9) = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9]
! Get number
nargs = command_argument_count()
if (nargs /= 1) then
stop
end if
call get_command_argument(1, arg, alen)
allocate(number(alen))
do i=1, alen
number(alen-i+1) = iachar(arg(i:i)) - iachar('0')
end do
! Calculate number
dr = 0
do i=1, alen
dr = dr + merge(drmap(number(i)), number(i), mod(i,2) == 0)
end do
if (mod(dr,10) == 0) then
write(*,'(a,i0)') arg(1:alen)//' is valid'
else
write(*,'(a,i0)') arg(1:alen)//' is not valid'
end if
end program luhn
! Results: ! 49927398716 is valid ! 49927398717 is not valid ! 1234567812345678 is not valid ! 1234567812345670 is valid</lang>
FreeBASIC
<lang FreeBASIC>' version 05-07-2015 ' compile with: fbc -s console
- Ifndef TRUE ' define true and false for older freebasic versions
#Define FALSE 0 #Define TRUE Not FALSE
- EndIf
Function luhntest(cardnr As String) As Integer
cardnr = Trim(cardnr) ' we don't want spaces Dim As String reverse_nr = cardnr Dim As Integer i, j, s1, s2, l = Len(cardnr) - 1
' reverse string
For i = 0 To l
reverse_nr[i] = cardnr[l - i]
Next
' sum odd numbers
For i = 0 To l Step 2
s1 = s1 + (reverse_nr[i] - Asc("0"))
Next
' sum even numbers
For i = 1 To l Step 2
j = reverse_nr[i] - Asc("0")
j = j * 2
If j > 9 Then j = j Mod 10 + 1
s2 = s2 + j
Next
If (s1 + s2) Mod 10 = 0 Then
Return TRUE
Else
Return FALSE
End If
End Function
' ------=< MAIN >=------
Dim As String input_nr(1 To ...) = {"49927398716", "49927398717",_
"1234567812345678", "1234567812345670"}
Dim As Integer a
Print "Task test number 49927398716 should be TRUE, report back as "; Print IIf(luhntest("49927398716" ) = TRUE, "TRUE", "FALSE") Print : Print
Print "test card nr:" For a = 1 To UBound(input_nr)
Print input_nr(a); " = "; IIf(luhntest(input_nr(a)) = TRUE, "TRUE", "FALSE")
Next
' empty keyboard buffer While InKey <> "" : Wend Print : Print "hit any key to end program" Sleep End</lang>
- Output:
Task test number 49927398716 should be TRUE, report back as TRUE test card nr: 49927398716 = TRUE 49927398717 = FALSE 1234567812345678 = FALSE 1234567812345670 = TRUE
FunL
<lang funl>def luhn_checksum( card_number ) =
def digits_of( n ) = [int(d) | d <- n.toString()] digits = digits_of( card_number ).reverse() odd_digits = digits(0:digits.length():2) even_digits = digits(1:digits.length():2) (sum( odd_digits ) + sum( sum(digits_of(d*2)) | d <- even_digits )) mod 10
def is_luhn_valid( card_number ) = luhn_checksum( card_number ) == 0
for n <- [49927398716, 49927398717, 1234567812345678, 1234567812345670]
println( n + ' is ' + (if is_luhn_valid(n) then 'valid' else 'invalid') )</lang>
- Output:
49927398716 is valid 49927398717 is invalid 1234567812345678 is invalid 1234567812345670 is valid
Gambas
Click this link to run this code <lang gambas>Public Sub Main() Dim sTrial As String[] = ["49927398716", "49927398717", "1234567812345678", "1234567812345670"] Dim sRev As String Dim siCount, siOdd, siEven, siHold, siQty As Short
For siQty = 0 To sTrial.Max
siOdd = 0 siEven = 0 sRev = ""
For siCount = Len(sTrial[siQty]) DownTo 1 sRev &= Mid(sTrial[siQty], siCount, 1) Next
For siCount = 1 To Len(sRev)
If Odd(siCount) Then siOdd += Val(Mid(sRev, siCount, 1))
If Even(siCount) Then
siHold = Val(Mid(sRev, siCount, 1)) * 2
If siHold > 9 Then
siEven += Val(Mid(Str(siHold), 1, 1)) + Val(Mid(Str(siHold), 2, 1))
Else
siEven += Val(Mid(sRev, siCount, 1)) * 2
End If
End If
Next
sRev = Str(siOdd + siEven) If sRev Ends "0" Then Print sTrial[siQty] & " is a valid number" Else Print sTrial[siQty] & " is NOT a valid number" End If
Next
End</lang> Output:
49927398716 is a valid number 49927398717 is NOT a valid number 1234567812345678 is NOT a valid number 1234567812345670 is a valid number
GAP
<lang gap>IsLuhn := function(n) local c, d, i, j, r; d := "0123456789"; j := 1; r := 0; for c in Reversed(String(n)) do i := Position(d, c); if i = fail then continue; fi; i := j*(i - 1); r := r + QuoInt(i, 10) + RemInt(i, 10); j := 3 - j; od; return RemInt(r, 10) = 0; end;
List([49927398716, 49927398717, 1234567812345678, 1234567812345670], IsLuhn);
- [ true, false, false, true ]
- Will also work on strings, and will skip non-digits
IsLuhn("4-992-739-871-6");
- true</lang>
Go
<lang go>package main
import (
"fmt" "strings"
)
const input = `49927398716 49927398717 1234567812345678 1234567812345670`
var t = [...]int{0, 2, 4, 6, 8, 1, 3, 5, 7, 9}
func luhn(s string) bool {
odd := len(s) & 1
var sum int
for i, c := range s {
if c < '0' || c > '9' {
return false
}
if i&1 == odd {
sum += t[c-'0']
} else {
sum += int(c - '0')
}
}
return sum%10 == 0
}
func main() {
for _, s := range strings.Split(input, "\n") {
fmt.Println(s, luhn(s))
}
}</lang>
- Output:
49927398716 true 49927398717 false 1234567812345678 false 1234567812345670 true
Groovy
<lang groovy>def checkLuhn(number) {
int total
(number as String).reverse().eachWithIndex { ch, index ->
def digit = Integer.parseInt(ch)
total += (index % 2 ==0) ? digit : [0, 2, 4, 6, 8, 1, 3, 5, 7, 9][digit]
}
total % 10 == 0
}</lang> Testing the function: <lang groovy>def verifyLuhn(number, expected) {
println "Checking: $number (${checkLuhn(number)})"
assert expected == checkLuhn(number)
}
[49927398716: true, 49927398717: false, 1234567812345678: false, 1234567812345670: true].each { number, expected ->
verifyLuhn number, expected
}</lang>
- Output:
Checking: 49927398716 (true) Checking: 49927398717 (false) Checking: 1234567812345678 (false) Checking: 1234567812345670 (true)
Haskell
<lang haskell>import Data.Char (digitToInt) luhn = (0 ==) . (`mod` 10) . sum . map (uncurry (+) . (`divMod` 10)) .
zipWith (*) (cycle [1,2]) . map digitToInt . reverse</lang>
- Output:
<lang haskell>map luhn ["49927398716", "49927398717", "1234567812345678", "1234567812345670"] [True,False,False,True]</lang>
Or, aiming for a legible relationship with the stages shown in the task description: <lang haskell>import Data.Char (digitToInt) import Data.List (transpose) import Data.List.Split (chunksOf)
luhn :: String -> Bool luhn x = 0 == rem (s1 + s2) 10
where
stringInts = fmap digitToInt
[odds, evens] =
(transpose . chunksOf 2)
(stringInts $ reverse x)
s1 = sum odds
s2 = sum $ sum . stringInts . show . (2 *) <$> evens
main :: IO () main =
mapM_
(print . ((,) <*> luhn))
[ "49927398716",
"49927398717",
"1234567812345678",
"1234567812345670"
]</lang>
- Output:
("49927398716",True)
("49927398717",False)
("1234567812345678",False)
("1234567812345670",True)
HicEst
<lang HicEst>CHARACTER numbers="49927398716 49927398717 1234567812345678 1234567812345670 "
DO nr = 1, 4
EDIT(Text=numbers, ITeM=nr, Parse=number)
sum_odds = 0
sum_even = 0
DO i = LEN(number), 1, -2
sum_odds = sum_odds + ICHAR(number(i)) - 48
IF(i > 1) THEN
even2 = 2 * (ICHAR(number(i-1)) - 48)
sum_even = sum_even + MOD(even2, 10) + INT(even2/10)
ENDIF
ENDDO
valid = (0 == MOD(sum_odds + sum_even, 10))
WRITE() number, " is ", "invalid"(1 + 2*valid:)
ENDDO</lang>
49927398716 is valid 49927398717 is invalid 1234567812345678 is invalid 1234567812345670 is valid
Icon and Unicon
We use map to pre-compute the sum of doubled digits. <lang icon>procedure main(aL) every write(i := !aL ," - ", ((\isluhn10(i),"valid")|"invalid") \ 1) end
procedure isluhn10(i) #: isluhn10(i) returns i (if i passes luhn10) or fails local sum
sum :=0 reverse(integer(i)) ? while not pos(0) do {
sum +:= move(1)
sum +:= map(move(1),"0123456789","0246813579")
}
return (sum % 10 = 0,i) end</lang>
- Output:
# luhn10 49927398716 49927398717 1234567812345678 1234567812345670 49927398716 - valid 49927398717 - invalid 1234567812345678 - invalid 1234567812345670 - valid
IS-BASIC
<lang IS-BASIC>100 PROGRAM "CredCard.bas" 110 DO 120 PRINT :PRINT "Credit card number:":INPUT PROMPT ">":CCN$ 130 IF CCN$="" THEN EXIT DO 140 IF LUHN(TRIM$(CCN$)) THEN 150 PRINT "Card number is valid." 160 ELSE 170 SET #102:INK 3:PRINT "Card number is invalid.":SET #102:INK 1 180 END IF 190 LOOP 200 DEF LUHN(CCN$) 210 LET L=LEN(CCN$):LET S=0 220 FOR I=1 TO L 230 LET N=VAL(CCN$(L-I+1)) 240 IF I BAND 1 THEN 250 LET S=S+N 260 ELSE 270 LET N=N*2:LET S=S+MOD(N,10)+INT(N/10) 280 END IF 290 NEXT 300 LET LUHN=MOD(S,10)=0 310 END DEF 320 DEF TRIM$(S$) 330 LET T$="" 340 FOR I=1 TO LEN(S$) 350 IF S$(I)>CHR$(47) AND S$(I)<CHR$(58) THEN LET T$=T$&S$(I) 360 NEXT 370 LET TRIM$=T$ 380 END DEF</lang>
Output:
Credit card number: >49927398716 Card number is valid. Credit card number: >49927398717 Card number is invalid. Credit card number: >1234 5678 1234 5678 Card number is invalid. Credit card number: >1234 5678 1234 5670 Card number is valid.
J
We can treat the odd digits the same as even digits, except that they are not doubled. Also, we do not need the intermediate sums.
<lang J>luhn=: 0 = 10 (| +/@,) 10 #.inv 1 2 *&|: _2 "."0\ |.</lang>
Example use: <lang J> luhn&> '49927398716';'49927398717';'1234567812345678';'1234567812345670' 1 0 0 1</lang>
Interpreting that example: In J, 1 is true, 0 is false, so the first and last provided digit sequences were valid and the middle two were not.
Java
<lang java>public class Luhn {
public static void main(String[] args) {
System.out.println(luhnTest("49927398716"));
System.out.println(luhnTest("49927398717"));
System.out.println(luhnTest("1234567812345678"));
System.out.println(luhnTest("1234567812345670"));
}
public static boolean luhnTest(String number){
int s1 = 0, s2 = 0;
String reverse = new StringBuffer(number).reverse().toString();
for(int i = 0 ;i < reverse.length();i++){
int digit = Character.digit(reverse.charAt(i), 10);
if(i % 2 == 0){//this is for odd digits, they are 1-indexed in the algorithm
s1 += digit;
}else{//add 2 * digit for 0-4, add 2 * digit - 9 for 5-9
s2 += 2 * digit;
if(digit >= 5){
s2 -= 9;
}
}
}
return (s1 + s2) % 10 == 0;
}
}</lang>
- Output:
true false false true
JavaScript
Using prototype. <lang javascript>mod10check = function(cc) {
return $A(cc).reverse().map(Number).inject(0, function(s, d, i) {
return s + (i % 2 == 1 ? (d == 9 ? 9 : (d * 2) % 9) : d);
}) % 10 == 0;
}; ['49927398716','49927398717','1234567812345678','1234567812345670'].each(function(i){alert(mod10check(i))});</lang>
Without any library. <lang javascript>var LuhnCheck = (function() { var luhnArr = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9]; return function(str) { var counter = 0; var incNum; var odd = false; var temp = String(str).replace(/[^\d]/g, ""); if ( temp.length == 0) return false; for (var i = temp.length-1; i >= 0; --i) { incNum = parseInt(temp.charAt(i), 10); counter += (odd = !odd)? incNum : luhnArr[incNum]; } return (counter%10 == 0); } })();</lang>
Highly compressed version. <lang javascript>var luhn10 = function(a,b,c,d,e) {
for(d = +a[b = a.length-1], e=0; b--;) c = +a[b], d += ++e % 2 ? 2 * c % 10 + (c > 4) : c; return !(d%10)
};
// returns true luhn10('4111111111111111')
// returns false luhn10('4111111111111112') </lang>
jq
<lang jq>def luhn:
def odds: . as $in | reduce range(0; length) as $i ([]; if ($i % 2) == 0 then . + [$in[$i]] else . end); def evens: . as $in | reduce range(1; length) as $i ([]; if ($i % 2) == 1 then . + [$in[$i]] else . end); def digits: map([.]|implode|tonumber); def sumdigits: tostring | explode | digits | add;
(tostring | explode | reverse ) as $reverse | ($reverse | odds | digits | add) as $s1 | ($reverse | evens | digits | map(. * 2 | sumdigits) | add) as $s2 | 0 == ($s1 + $s2) % 10 ;</lang>
Example <lang jq> ( 49927398716,
49927398717, 1234567812345678, 1234567812345670 ) | "\(.) => \(luhn)";</lang>
- Output:
$ jq -r -M -n -f luhn.jq 49927398716 => true 49927398717 => false 1234567812345678 => false 1234567812345670 => true
Julia
The test function itself is only a single line of code:
<lang Julia>luhntest(x::Integer) = (sum(digits(x)[1:2:end]) + sum(map(x -> sum(digits(x)), 2 * digits(x)[2:2:end]))) % 10 == 0</lang>
More readable version:
<lang julia>function luhntest(x::Integer)
d = reverse(digits(x)) s = sum(d[1:2:end]) s += sum(sum.(digits.(2d[2:2:end]))) return s % 10 == 0
end
for card in [49927398716, 49927398717, 1234567812345678, 1234567812345670]
println(luhntest(card) ? "PASS " : "FAIL ", card)
end</lang>
- Output:
PASS 49927398716 FAIL 49927398717 FAIL 1234567812345678 PASS 1234567812345670
K
<lang k>so: {+/x@2*!_ceil(#x)%2} se: {+/{+/0$'$x}'2*x@1+2*!(#x)%2} luhn: {n:|0$'$x; 0=((se n)+so n)!10}</lang>
<lang k>luhn2: {~(+/,//10_vs'1 2*+-1 2#((#n)!2){x,0}/n:0$'|$x)</lang>
Example:
<lang k> luhn'49927398716 49927398717 1234567812345678 1234567812345670 1 0 0 1
luhn2'49927398716 49927398717 1234567812345678 1234567812345670
1 0 0 1</lang>
<lang k>luhn:{[cc]
digits:0$/:|cc / convert chars to digit ints s:digits*(#cc)#1 2 / evens doubled, odds not nines:+/s>9 / number of sums greater than 9 :~((+/s)-(9*nines))!10 / sum minus the nines is mod ten? }</lang>
Example:
<lang k> test:("49927398716";"49927398717";"1234567812345678";"1234567812345670")
luhn'test
1 0 0 1</lang>
Kotlin
<lang scala>// version 1.0
fun checkLuhn(number: String): Boolean {
var isOdd = true var sum = 0
for (index in number.indices.reversed()) {
val digit = number[index] - '0'
sum += if (isOdd) digit else (digit * 2).let { (it / 10) + (it % 10) }
isOdd = !isOdd
}
return (sum % 10) == 0
}
fun main(args: Array<String>) {
val numbers = arrayOf("49927398716", "49927398717", "1234567812345678", "1234567812345670")
for (number in numbers)
println("${number.padEnd(16)} is ${if(checkLuhn(number)) "valid" else "invalid"}")
}</lang>
- Output:
49927398716 is valid 49927398717 is invalid 1234567812345678 is invalid 1234567812345670 is valid
langur
<lang langur>val .luhntest = f(.s) {
val .t = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9] val .numbers = s2n .s val .oddeven = len(.numbers) rem 2
for[=0] .i of .numbers {
_for += if(.i rem 2 == .oddeven: .numbers[.i]; .t[.numbers[.i]+1])
} div 10
}
val .tests = h{
"49927398716": true, "49927398717": false, "1234567812345678": false, "1234567812345670": true,
}
for .key of .tests {
val .pass = .luhntest(.key) write .key, ": ", .pass writeln if(.pass == .tests[.key]: ""; " (LUHN TEST FAILED)")
}</lang>
- Output:
49927398717: false 49927398716: true 1234567812345678: false 1234567812345670: true
Lasso
Part of the Lasso's implementation of "valid_creditcard". <lang lasso>#!/usr/bin/lasso9
define luhn_check(number) => {
local(
rev = #number->asString,
checksum = 0
)
#rev->reverse
iterate(#rev, local(digit)) => {
if((loop_count % 2) == 0) => {
#checksum += (2 * integer(#digit))
integer(#digit) >= 5 ? #checksum -= 9
else
#checksum += integer(#digit)
}
}
(#checksum % 10) != 0 ? return false
return true
}
stdoutnl(luhn_check(49927398716)) // true stdoutnl(luhn_check(49927398717)) // false stdoutnl(luhn_check(1234567812345678)) // false stdoutnl(luhn_check(1234567812345670)) // true</lang>
Liberty BASIC
<lang lb>' [RC] Luhn test
card$(1)="49927398716" card$(2)="49927398717" card$(3)="1234567812345678" card$(4)="1234567812345670"
for test = 1 to 4
odd=1
sum = 0
for n = len(card$(test)) to 1 step -1
num=val(mid$(card$(test),n,1))
if odd then
sum = sum + num
odd=0
else
num=num*2
if num<=9 then
sum = sum + num
else
sum = sum + val(left$(str$(num),1)) + val(right$(str$(num),1))
end if
odd=1
end if
next
if sum mod 10 = 0 then
print card$(test),"True"
else
print card$(test),"False"
end if
next</lang>
LiveCode
<lang LiveCode>function LuhnTest cc
local s1,evens, s2
repeat with n = 1 to len(cc)
if n mod 2 is not 0 then
add (char -n of cc) to s1
else
put (char -n of cc) * 2 into evens
if evens > 9 then subtract 9 from evens
add evens to s2
end if
end repeat
return the last char of (s1 + s2) is 0
end LuhnTest
-- test repeat for each item ccno in "49927398716,49927398717,1234567812345678,1234567812345670"
put ccno && LuhnTest(ccno) & cr after luhncheck
end repeat put luhncheck
49927398716 true 49927398717 false 1234567812345678 false 1234567812345670 true </lang>
Logo
<lang logo>to small? :list
output or [empty? :list] [empty? bf :list]
end to every.other :list
if small? :list [output :list] output fput first :list every.other bf bf :list
end to wordtolist :word
output map.se [?] :word
end
to double.digit :digit
output item :digit {0 2 4 6 8 1 3 5 7 9}@0
; output ifelse :digit < 5 [2*:digit] [1 + modulo 2*:digit 10]
end
to luhn :credit
localmake "digits reverse filter [number? ?] wordtolist :credit localmake "s1 apply "sum every.other :digits localmake "s2 apply "sum map "double.digit every.other bf :digits output equal? 0 last sum :s1 :s2
end
show luhn "49927398716 ; true show luhn "49927398717 ; false show luhn "1234-5678-1234-5678 ; false show luhn "1234-5678-1234-5670 ; true</lang>
Lua
<lang Lua>function luhn(n)
n=string.reverse(n) print(n) local s1=0 --sum odd digits for i=1,n:len(),2 do s1=s1+n:sub(i,i) end --evens local s2=0 for i=2,n:len(),2 do local doubled=n:sub(i,i)*2 doubled=string.gsub(doubled,'(%d)(%d)',function(a,b)return a+b end) s2=s2+doubled end print(s1) print(s2) local total=s1+s2 if total%10==0 then return true end return false
end
-- Note that this function takes strings, not numbers. -- 16-digit numbers tend to be problematic -- when looking at individual digits. print(luhn'49927398716') print(luhn'49927398717') print(luhn'1234567812345678') print(luhn'1234567812345670')</lang>
M2000 Interpreter
<lang M2000 Intertrpeter> Module Checkit {
Function luhntest(cardnr$) {
cardnr$ = Trim$(cardnr$) ' we don't want spaces
if len(cardnr$)=0 then exit
Dim Base 0, reverse_nr$(Len(cardnr$))
Def integer i, j, s1, s2, l , l2
Let l=Len(cardnr$)-1, l2=l+1
' reverse string
For i = 0 To l
reverse_nr$(i) = mid$(cardnr$,l2-i,1)
Next i
' sum odd numbers
For i = 0 To l Step 2
s1 = s1 + (Asc(reverse_nr$(i)) - Asc("0"))
Next i
' sum even numbers
For i = 1 To l Step 2
j = Asc(reverse_nr$(i)) - Asc("0")
j = j * 2
If j > 9 Then j = j Mod 10 + 1
s2 = s2 + j
Next i
If (s1 + s2) Mod 10 = 0 Then
= 1=1
Else
= 1=0
End If
}
Flush
Data "49927398716", "49927398717", "1234567812345678", "1234567812345670"
while not empty
over
print letter$;" = ";luhntest(letter$)
end while
} Checkit </lang>
- Output:
49927398716 = True 49927398717 = False 1234567812345678 = False 1234567812345670 = True
Mathematica
<lang Mathematica>LuhnQ[nb_] := (Mod[Total[(2*ToExpression[#2;;All;;2]) /. {z_?(Function[v, v>9]) -> z-9}]
+ Total[ToExpression[#1;;All;;2]], 10] == 0)& [Characters[StringReverse[ToString[nb]]] ]
LuhnQ /@ {49927398716, 49927398717, 1234567812345678, 1234567812345670} ->{True, False, False, True}</lang>
Alternate Code
Eliminates conversion of numbers to strings and back <lang Mathematica>LuhnQ[n_Integer] :=
Block[{digits = Reverse@IntegerDigits@n},
Mod[Total[{digits;; ;; 2,
IntegerDigits[2 #] & /@ digits2 ;; ;; 2}, -1], 10] == 0]
LuhnQ /@ {49927398716, 49927398717, 1234567812345678, 1234567812345670}</lang>
- Output:
{True,False,False,True}
MATLAB
The solution is basically the same as for Octave. <lang MATLAB>function passed = luhn(num) if nargin == 0 % evaluate test cases
testnum = [49927398716 49927398717 1234567812345678 1234567812345670]; for num = testnum disp([int2str(num) ': ' int2str(luhn(num))]) end return
end % luhn function starts here d = int2str(num) - '0'; % convert number into vector of digits m = [2:2:8,1:2:9]; % rule 3: maps 1:9 to [2 4 6 8 1 3 5 7 9] passed = ~mod(sum(d(end:-2:1)) + sum(m(d(end-1:-2:1))), 10); end</lang>
- Output:
49927398716: 1 49927398717: 0 1234567812345678: 0 1234567812345670: 1
min
<lang min>((dup 10 <) 'quote (((10 mod) (10 div)) cleave) 'cons linrec) :digits ((0 0) dip (pop 'succ dip over even?) partition ((pop pop) dip) dip) :evens/odds ((2 * digits sum) map sum) :evens-sum (digits evens/odds ('evens-sum 'sum) => spread + 10 mod 0 ==) :luhn?
(49927398716 49927398717 1234567812345678 1234567812345670) (dup print! " " print! luhn? puts!) foreach</lang>
- Output:
49927398716 true 49927398717 false 1234567812345678 false 1234567812345670 true
MiniScript
<lang MiniScript>isValid = function(s)
sum = 0
odd = true
for i in range(s.len-1)
d = val(s[i])
sum = sum + d * (2 - odd)
if not odd and d > 4 then sum = sum - 9
odd = not odd
end for
return sum % 10 == 0
end function
test = function(s)
if isValid(s) then print s + ": valid" else print s + ": invalid"
end function
test "49927398716" test "49927398717" test "1234567812345678" test "1234567812345670"</lang>
- Output:
49927398716: valid 49927398717: invalid 1234567812345678: invalid 1234567812345670: valid
MUMPS
<lang mumps>LUHN(C)
NEW ODD,EVEN,S SET S=$REVERSE(C) SET ODD=0 FOR I=1:2:$LENGTH(S) SET ODD=ODD+$EXTRACT(S,I) SET EVEN=0 FOR I=2:2:$LENGTH(S) SET T=$EXTRACT(S,I)*2 SET EVEN=EVEN+$SELECT(T<=9:T,T>9:$EXTRACT(T,1)+$EXTRACT(T,2)) QUIT '((ODD+EVEN)#10)</lang>
USER>W !,$S($$LUHN^ROSETTA("49927398716")=0:"INVALID",1:"VALID")
VALID
USER>W !,$S($$LUHN^ROSETTA("49927398717")=0:"INVALID",1:"VALID")
INVALID
USER>W !,$S($$LUHN^ROSETTA("1234567812345678")=0:"INVALID",1:"VALID")
INVALID
USER>W !,$S($$LUHN^ROSETTA("1234567812345670")=0:"INVALID",1:"VALID")
VALID
Nanoquery
<lang Nanoquery>def reverse_str(string)
to_return = ""
for i in range(len(string) - 1, 0, -1)
to_return += string[i]
end for
return to_return
end reverse_str
def luhnTest(number)
s1 = 0; s2 = 0
reversed = reverse_str(number)
for i in range(0, len(reversed) - 1)
digit = int(reversed[i])
if (i % 2) = 0
s1 += digit
else
s2 += 2 * digit
if digit >= 5
s2 -= 9
end if
end if
end for
return ((s1 + s2) % 10) = 0
end luhnTest
println luhnTest("49927398716") println luhnTest("49927398717") println luhnTest("1234567812345678") println luhnTest("1234567812345670")</lang>
- Output:
true false false true
NetRexx
<lang netrexx>
class LuhnTest
method main(args=String[]) static
cc = 0
cc[1] = '49927398716'
cc[2] = '49927398717'
cc[3] = '1234567812345678'
cc[4] = '1234567812345670'
loop k=1 while cc[k] <> 0
r = checksum(cc[k])
if r==0 then say cc[k].right(20) 'passed'
else say cc[k].right(20) 'failed'
end
-- Luhn algorithm checksum for credit card numbers
method checksum(t) static
if t.length()//2 then t = '0't --pad # on left with 0
t = t.reverse()
s = 0
loop j = 1 to t.length()-1 by 2
q = 2*t.substr(j+1,1)
if q>9 then q = q.left(1) + q.right(1)
s= s+t.substr(j,1)+q
end
return s//10\==0
</lang>
Nim
<lang nim>proc luhn(cc: string): bool =
const m = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9]
var sum = 0
var odd = true
for i in countdown(cc.high, 0):
let digit = ord(cc[i]) - ord('0')
sum += (if odd: digit else: m[digit])
odd = not odd
result = sum mod 10 == 0
for cc in ["49927398716", "49927398717", "1234567812345678", "1234567812345670"]:
echo cc, ' ', luhn(cc)</lang>
- Output:
49927398716 true 49927398717 false 1234567812345678 false 1234567812345670 true
Objeck
<lang objeck>bundle Default {
class Luhn {
function : IsValid(cc : String) ~ Bool {
isOdd := true;
oddSum := 0;
evenSum := 0;
for(i := cc->Size() - 1; i >= 0; i -= 1;) {
digit : Int := cc->Get(i) - '0';
if(isOdd) {
oddSum += digit;
}
else {
evenSum += digit / 5 + (2 * digit) % 10;
};
isOdd := isOdd <> true;
};
return (oddSum + evenSum) % 10 = 0;
}
function : Main(args : String[]) ~ Nil {
IsValid("49927398716")->PrintLine();
IsValid("49927398717")->PrintLine();
IsValid("1234567812345678")->PrintLine();
IsValid("1234567812345670")->PrintLine();
}
}
}</lang>
Objective-C
<lang objc>- (NSArray *) toCharArray {
NSMutableArray *characters = [[NSMutableArray alloc] initWithCapacity:[self length]]; for (int i=0; i < [self length]; i++) { NSString *ichar = [NSString stringWithFormat:@"%C", [self characterAtIndex:i]]; [characters addObject:ichar]; }
return characters; }
+ (BOOL) luhnCheck:(NSString *)stringToTest {
NSArray *stringAsChars = [stringToTest toCharArray];
BOOL isOdd = YES; int oddSum = 0; int evenSum = 0;
for (int i = [stringToTest length] - 1; i >= 0; i--) {
int digit = [(NSString *)stringAsChars[i] intValue];
if (isOdd) oddSum += digit; else evenSum += digit/5 + (2*digit) % 10;
isOdd = !isOdd; }
return ((oddSum + evenSum) % 10 == 0); }
BOOL test0 = [self luhnCheck:@"49927398716"]; //Result = YES BOOL test1 = [self luhnCheck:@"49927398717"]; //Result = NO BOOL test2 = [self luhnCheck:@"1234567812345678"]; //Result = NO BOOL test3 = [self luhnCheck:@"1234567812345670"]; //Result = YES</lang>
OCaml
<lang ocaml>let luhn s =
let rec g r c = function
| 0 -> r
| i ->
let d = c * ((int_of_char s.[i-1]) - 48) in
g (r + (d/10) + (d mod 10)) (3-c) (i-1)
in
(g 0 1 (String.length s)) mod 10 = 0
- </lang>
- Output:
<lang ocaml># List.map luhn [ "49927398716"; "49927398717"; "1234567812345678"; "1234567812345670" ];; - : bool list = [true; false; false; true]</lang>
Octave
<lang Octave> function y = isluhn(s); if isnumeric(s) s = mat2str(s); end; % make sure s is a string d = s-'0'; % convert string into vector of digits m = [2:2:8,1:2:9]; % rule 3: maps [1:9] -> i y = ~mod(sum(d(end:-2:1)) + sum(m(d(end-1:-2:1))),10);
end; </lang>
- Output:
<lang octave> isluhn('49927398716') ans = 1
isluhn('49927398717')
ans = 0
isluhn('1234567812345678')
ans = 0
isluhn('1234567812345670')
ans = 1 </lang>
Oforth
<lang Oforth>: luhnTest(n) | s i |
n asString reverse ->s
0 s size loop: i [
i s at asDigit
i isEven ifTrue: [ 2 * dup 10 >= ifTrue: [ 9 - ] ] +
]
10 mod ==0 ; </lang>
- Output:
[ 49927398716, 49927398717, 1234567812345678, 1234567812345670 ] map(#luhnTest) println [1, 0, 0, 1]
OpenEdge/Progress
<lang progress>FUNCTION fnLuhnAlgorithm RETURNS LOGICAL
(INPUT pcNumber AS CHARACTER):
/*------------------------------------------------------------------------------
Purpose: Applies Luhn Algorithm to check a Number Notes: Returns True/False Validation based on check digit
*/
DEFINE VARIABLE cNum AS CHARACTER NO-UNDO. DEFINE VARIABLE iCheck AS INTEGER NO-UNDO. DEFINE VARIABLE iLength AS INTEGER NO-UNDO. DEFINE VARIABLE iLoopCnt AS INTEGER NO-UNDO. DEFINE VARIABLE iNum AS INTEGER NO-UNDO. DEFINE VARIABLE iNum1 AS INTEGER NO-UNDO. DEFINE VARIABLE iNum2 AS INTEGER NO-UNDO. DEFINE VARIABLE iTestLength AS INTEGER NO-UNDO.
ASSIGN
iLength = LENGTH(pcNumber)
iTestLength = iLength - 1
iCheck = 1. /* 1 for the check digit we skip */
DO iLoopCnt = iTestLength TO 1 BY -1:
ASSIGN
iNum = INTEGER(SUBSTR(pcNumber,iLoopCnt,1))
iCheck = iCheck + 1.
IF iCheck MODULO 2 = 1 THEN
ASSIGN iNum1 = iNum1 + iNum.
ELSE
DO:
ASSIGN iNum2 = iNum * 2.
IF iNum2 < 10 THEN
ASSIGN iNum1 = iNum1 + iNum2.
ELSE
ASSIGN
cNum = STRING(iNum2)
iNum1 = iNum1 + INTEGER(SUBSTR(cNum,1,1)) + INTEGER(SUBSTR(cNum,2,1)).
END.
END.
ASSIGN
iNum2 = iNum1 * 9
iNum = iNum2 MODULO 10.
IF iNum = INTEGER(SUBSTR(pcNumber,iLength,1)) THEN
RETURN TRUE.
ELSE
RETURN FALSE.
END FUNCTION. /* fnLuhnAlgorithm */</lang>
- Output:
49927398716 - yes 49927398717 - no 1234567812345678 - no 1234567812345670 - yes
Order
This example highlights Order's unusual treatment of numbers.
Numbers larger than 100 are not recognized by the interpreter in literal form and must instead be entered as "native" numbers (i.e. listing the separate digits as arguments to 8nat).
Since internally, a native number is just a sequence of the digits in reverse order with an end digit marker, converting the number into a reversed list of digits mainly involves removing this terminator, so that we can immediately treat the digits as number elements.
<lang c>#include <order/interpreter.h>
- define ORDER_PP_DEF_8luhn ORDER_PP_FN( \
8fn(8N, 8if(8is_seq(8N), 8luhn_wk(8num_to_seq(8N)), 8false)) )
- define ORDER_PP_DEF_8num_to_seq ORDER_PP_FN( \
8fn(8N, 8seq_push_back(8seq(8seq_last(8N)), 8seq_pop_back(8N))) )
- define ORDER_PP_DEF_8luhn_wk ORDER_PP_FN( \
8fn(8N, \
8lets((8P, 8unzip(8N, 8nil, 8nil, 8true)) \
(8O, 8seq_fold(8plus, 0, 8tuple_at_0(8P))) \
(8E, 8seq_fold(8plus, 0, \
8seq_map(8dig_map, 8tuple_at_1(8P)))), \
8is_0(8remainder(8plus(8O, 8E), 10)))) )
- define ORDER_PP_DEF_8dig_map ORDER_PP_FN( \
8fn(8X, 8tuple_at(8X, 8tuple(0,2,4,6,8,1,3,5,7,9))) )
- define ORDER_PP_DEF_8unzip ORDER_PP_FN( \
8fn(8S, 8L, 8R, 8O, \
8if(8is_nil(8S), \
8pair(8L, 8R), \
8if(8O, \
8unzip(8seq_tail(8S), 8seq_push_back(8seq_head(8S), 8L), \
8R, 8false), \
8unzip(8seq_tail(8S), 8L, \
8seq_push_back(8seq_head(8S), 8R), 8true)))) )
ORDER_PP(8seq_to_tuple(
8seq_map(8luhn, 8seq(8nat(4,9,9,2,7,3,9,8,7,1,6),
8nat(4,9,9,2,7,3,9,8,7,1,7),
8nat(1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8),
8nat(1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,0)))
))</lang>
- Output:
<lang>(8true,8false,8false,8true)</lang>
Oz
<lang oz>declare
fun {Luhn N}
{Sum {List.mapInd {Reverse {Digits N}}
fun {$ Idx Dig}
if {IsEven Idx} then {Sum {Digits 2*Dig}}
else Dig
end
end}}
mod 10 == 0
end
fun {Digits N}
{Map {Int.toString N} fun {$ D} D - &0 end}
end
fun {Sum Xs}
{FoldL Xs Number.'+' 0}
end
in
{Show
{Map
[49927398716 49927398717 1234567812345678 1234567812345670]
Luhn}}</lang>
Pascal
<lang Pascal>program luhn;
function lunh(arg: string): boolean;
var
i, sum: integer;
temp: byte;
begin
sum := 0;
for i:= length(arg) downto 1 do begin // Run the characters backwards
temp := byte(arg[i])-48; // Convert from ASCII to byte
if (length(arg)-i) mod 2 = 0
then sum := sum + temp // Odd characters just add
else if temp < 5
then sum := sum + 2*temp // Even characters add double
else sum := sum + (2*temp)-9; // or sum the digits of the doubling
end;
result := sum mod 10 = 0; // Return true if sum ends in a 0
end;
begin
writeln(' 49927398716: ', lunh('49927398716'));
writeln(' 49927398717: ', lunh('49927398717'));
writeln('1234567812345678: ', lunh('1234567812345678'));
writeln('1234567812345670: ', lunh('1234567812345670'));
end.</lang>
- Output:
49927398716: TRUE
49927398717: FALSE
1234567812345678: FALSE
1234567812345670: TRUE
Perl
<lang perl>sub luhn_test {
my @rev = reverse split //,$_[0];
my ($sum1,$sum2,$i) = (0,0,0);
for(my $i=0;$i<@rev;$i+=2)
{
$sum1 += $rev[$i];
last if $i == $#rev;
$sum2 += 2*$rev[$i+1]%10 + int(2*$rev[$i+1]/10);
}
return ($sum1+$sum2) % 10 == 0;
} print luhn_test('49927398716'); print luhn_test('49927398717'); print luhn_test('1234567812345678'); print luhn_test('1234567812345670');</lang>
Or using map( ) and a precomputed array:
<lang Perl>sub luhn {
my (@n,$i,$sum) = split //, reverse $_[0];
my @a = map {int(2*$_ / 10) + (2*$_ % 10)} (0..9);
map {$sum += $i++ % 2 ? $a[$_] : $_} @n;
return ($sum % 10) ? 0 : 1;
}
- Test and display
map {print luhn($_), ": $_\n"}
qw(49927398716 49927398717 1234567812345678 1234567812345670);</lang>
- Output:
1: 49927398716 0: 49927398717 0: 1234567812345678 1: 1234567812345670
Phix
<lang Phix>function Luhn(string st) integer s=0, d
for i=1 to length(st) do
d = st[i]-'0'
s += iff(mod(i,2)?d,d*2-(d>4)*9)
end for
return remainder(s,10)=0
end function
procedure test(string s)
printf(1,"%20s : %s\n",{s,iff(Luhn(reverse(s))?"OK":"FAIL")})
end procedure
test("49927398716") test("49927398717") test("1234567812345678") test("1234567812345670")</lang>
- Output:
49927398716 : OK
49927398717 : FAIL
1234567812345678 : FAIL
1234567812345670 : OK
PHP
<lang php>$numbers = "49927398716 49927398717 1234567812345678 1234567812345670"; foreach (split(' ', $numbers) as $n)
echo "$n is ", luhnTest($n) ? 'valid' : 'not valid', '
';
function luhnTest($num) {
$len = strlen($num);
for ($i = $len-1; $i >= 0; $i--) {
$ord = ord($num[$i]);
if (($len - 1) & $i) {
$sum += $ord;
} else {
$sum += $ord / 5 + (2 * $ord) % 10;
}
}
return $sum % 10 == 0;
}</lang>
- Output:
49927398716 is valid 49927398717 is not valid 1234567812345678 is not valid 1234567812345670 is valid
And a more concise example using PHP core methods: <lang php>function luhn_test($num) {
$str = ; foreach( array_reverse( str_split( $num ) ) as $i => $c ) $str .= ($i % 2 ? $c * 2 : $c ); return array_sum( str_split($str) ) % 10 == 0;
}
foreach (array('49927398716','49927398717','1234567812345678','1234567812345670') as $n)
echo "$n is ", luhn_test($n) ? 'valid' : 'not valid', "
\n";</lang>
- Output:
49927398716 is valid 49927398717 is not valid 1234567812345678 is not valid 1234567812345670 is valid
PicoLisp
<lang PicoLisp>(de luhn (Num) # 'Num' may be a number or a string
(=0
(%
(sum
'((C F)
(setq C (- (char C) 48))
(if F
C # Odd
(+ (/ C 5) (% (* 2 C) 10)) ) ) # Even
(flip (chop Num))
'(T NIL .) )
10 ) ) )</lang>
- Output:
: (mapcar luhn (49927398716 49927398717 1234567812345678 1234567812345670)) -> (0 NIL NIL 0)
PL/I
<lang pli>test: procedure options (main);
declare (cardnumber, rcn) character (20) varying; declare (i, k, s1, s2) fixed binary;
get edit (cardnumber) (L);
cardnumber = trim(cardnumber);
rcn = reverse(cardnumber);
s1, s2 = 0;
/* Sum the odd-numbered digits */
do i = 1 to length(rcn) by 2;
s1 = s1 + substr(rcn, i, 1);
end;
/* Twice the even-numbered digits. */
do i = 2 to length(rcn) by 2;
k = 2 * substr(rcn, i, 1);
s2 = s2 + mod(k,10) + trunc(k/10);
end;
if mod(s1 + s2, 10) = 0 then
put skip edit (cardnumber, ' passes the Luhn test' )(a);
else
put skip edit (cardnumber, ' does not pass the Luhn test' )(a);
put skip list (s1 + s2);
end test;</lang>
- Output:
49927398716 passes the Luhn test
70
49927398717 does not pass the Luhn test
71
1234567812345678 does not pass the Luhn test
68
1234567812345670 passes the Luhn test
60
Comment: it isn't necessary to reverse the string in order to perform the test.
PL/SQL
<lang PLSQL>FUNCTION algoLuhn ( p_numeroVerif VARCHAR2 )
RETURN NUMBER
IS
i NUMBER;
v_NBi SMALLINT;
v_retour SMALLINT;
v_somme NUMBER := 0;
v_nbCar NUMBER;
BEGIN
v_nbCar := LENGTH(p_numeroVerif);
FOR i IN 1..v_nbCar
LOOP
v_NBi := TO_NUMBER(SUBSTR(p_numeroVerif,v_nbCar+1-i,1));
v_somme := v_somme
+ MOD(i,2) * v_NBi
+ MOD(i+1,2) * SIGN(-SIGN(v_Nbi-4)+1) * (2*v_NBi)
+ MOD(i+1,2) * SIGN( SIGN(v_Nbi-5)+1) * (2*v_NBi-9);
END LOOP;
v_retour := SIGN(MOD(v_somme,10));
RETURN v_retour;
EXCEPTION
WHEN OTHERS
THEN
RETURN 1;
END algoLuhn;</lang>
Plain English
<lang plainenglish>To run: Start up. Test whether "49927398716" will pass the luhn test. Test whether "49927398717" will pass the luhn test. Test whether "1234567812345678" will pass the luhn test. Test whether "1234567812345670" will pass the luhn test. Wait for the escape key. Shut down.
To test whether a string will pass the luhn test: Write the string then ": " on the console without advancing. If the string will pass the luhn test, write "valid" on the console; exit. Write "invalid" on the console.
A sum is a number.
To decide if a string will pass the luhn test: If the string is blank, say no. Privatize the string. Reverse the string. Put 0 into a first sum. Put 0 into a second sum. Put 1 into a count. Slap a rider on the string. Loop. If the rider's source is blank, break. Put the rider's source's first's target into a byte. If the byte is not any digit, say no. Convert the byte to a number. If the count is odd, add the number to the first sum; bump the count; bump the rider; repeat. Double the number. If the number is greater than 9, digital root the number. Add the number to the second sum. Bump the count. Bump the rider. Repeat. If the first sum plus the second sum is evenly divisible by 10, say yes. Say no.
To digital root a number: Divide the number by 10 giving a quotient and a remainder. Put the quotient plus the remainder into the number.
To convert a byte to a number: If the byte is any digit, put the byte minus 48 into the number.</lang>
- Output:
49927398716: valid 49927398717: invalid 1234567812345678: invalid 1234567812345670: valid
PowerBASIC
<lang powerbasic>#COMPILE EXE
- DIM ALL
- COMPILER PBCC 6
FUNCTION LuhnCheckPassed(BYVAL dgts AS STRING) AS INTEGER LOCAL i, s, s1 AS DWORD
dgts = STRREVERSE$(dgts)
FOR i = 1 TO LEN(dgts) STEP 2
s += VAL(MID$(dgts, i, 1))
NEXT i
FOR i = 2 TO LEN(dgts) STEP 2
s1 = 2 * VAL(MID$(dgts, i, 1))
IF s1 >= 10 THEN
s -= 9
END IF
s += s1
NEXT i
FUNCTION = NOT ISTRUE (s MOD 10)
END FUNCTION
FUNCTION PBMAIN () AS LONG
' this test is expected to pass:
CON.PRINT IIF$(LuhnCheckPassed("49927398716"), "passed", "failed")
' this test is expected to fail:
CON.PRINT IIF$(LuhnCheckPassed("49927398717"), "passed", "failed")
' this test is expected to fail:
CON.PRINT IIF$(LuhnCheckPassed("1234567812345678"), "passed", "failed")
' this test is expected to pass:
CON.PRINT IIF$(LuhnCheckPassed("1234567812345670"), "passed", "failed")
END FUNCTION</lang>
- Output:
passed failed failed passed
PowerShell
<lang PowerShell> function Test-LuhnNumber {
<#
.SYNOPSIS
Tests validity of credit card numbers.
.DESCRIPTION
Tests validity of credit card numbers using the Luhn test.
.PARAMETER Number
The number must be 11 or 16 digits.
.EXAMPLE
Test-LuhnNumber 49927398716
.EXAMPLE
[int64[]]$numbers = 49927398716, 49927398717, 1234567812345678, 1234567812345670
C:\PS>$numbers | ForEach-Object {
"{0,-17}: {1}" -f $_,"$(if(Test-LuhnNumber $_) {'Is valid.'} else {'Is not valid.'})"
}
#>
[CmdletBinding()]
[OutputType([bool])]
Param
(
[Parameter(Mandatory=$true,
Position=0)]
[ValidateScript({$_.Length -eq 11 -or $_.Length -eq 16})]
[ValidatePattern("^\d+$")]
[string]
$Number
)
$digits = ([Regex]::Matches($Number,'.','RightToLeft')).Value
$digits |
ForEach-Object `
-Begin {$i = 1} `
-Process {if ($i++ % 2) {$_}} |
ForEach-Object `
-Begin {$sumOdds = 0} `
-Process {$sumOdds += [Char]::GetNumericValue($_)}
$digits |
ForEach-Object `
-Begin {$i = 0} `
-Process {if ($i++ % 2) {$_}} |
ForEach-Object `
-Process {[Char]::GetNumericValue($_) * 2} |
ForEach-Object `
-Begin {$sumEvens = 0} `
-Process {
$_number = $_.ToString()
if ($_number.Length -eq 1)
{
$sumEvens += [Char]::GetNumericValue($_number)
}
elseif ($_number.Length -eq 2)
{
$sumEvens += [Char]::GetNumericValue($_number[0]) + [Char]::GetNumericValue($_number[1])
}
}
($sumOdds + $sumEvens).ToString()[-1] -eq "0"
} </lang> <lang PowerShell> Test-LuhnNumber 49927398716 </lang>
- Output:
True
<lang PowerShell> 49927398716, 49927398717, 1234567812345678, 1234567812345670 | ForEach-Object {
"{0,-17}: {1}" -f $_,"$(if(Test-LuhnNumber $_) {'Is valid.'} else {'Is not valid.'})"
} </lang>
- Output:
49927398716 : Is valid. 49927398717 : Is not valid. 1234567812345678 : Is not valid. 1234567812345670 : Is valid.
PureBasic
<lang PureBasic>DataSection
Sample: Data.s "49927398716" Data.s "49927398717" Data.s "1234567812345678" Data.s "1234567812345670" Data.s ""
EndDataSection
Procedure isValid(cardNumber.s)
Protected i, length, s1, s2, s2a cardNumber = ReverseString(cardNumber) length = Len(cardNumber) For i = 1 To length Step 2 s1 + Val(Mid(cardNumber, i, 1)) Next
For i = 2 To length Step 2
s2a = Val(Mid(cardNumber, i, 1)) * 2
If s2a < 10
s2 + s2a
Else
s2 + 1 + Val(Right(Str(s2a), 1))
EndIf
Next
If Right(Str(s1 + s2), 1) = "0"
ProcedureReturn #True
Else
ProcedureReturn #False
EndIf
EndProcedure
If OpenConsole()
Define cardNumber.s
Restore Sample
Repeat
Read.s cardNumber
If cardNumber <> ""
Print(cardNumber + " is ")
If isValid(cardNumber)
PrintN("valid")
Else
PrintN("not valid")
EndIf
EndIf
Until cardNumber = ""
Print(#CRLF$ + #CRLF$ + "Press ENTER to exit")
Input()
CloseConsole()
EndIf</lang>
- Output:
49927398716 is valid 49927398717 is not valid 1234567812345678 is not valid 1234567812345670 is valid
Python
Functional
The divmod in the function below conveniently splits a number into its two digits ready for summing: <lang python>>>> def luhn(n): r = [int(ch) for ch in str(n)][::-1] return (sum(r[0::2]) + sum(sum(divmod(d*2,10)) for d in r[1::2])) % 10 == 0
>>> for n in (49927398716, 49927398717, 1234567812345678, 1234567812345670): print(n, luhn(n))</lang>
- Output:
49927398716 True 49927398717 False 1234567812345678 False 1234567812345670 True
Or, using itertools cycle with map and reduce:
<lang python>Luhn test of credit card numbers
from operator import add, mul from functools import reduce from itertools import cycle
- luhn :: Integer -> Bool
def luhn(n):
True if n is a valid Luhn credit card number.
def divMod10Sum(a, x):
return a + add(*divmod(x, 10))
return 0 == reduce(
divMod10Sum,
map(
mul,
cycle([1, 2]),
map(int, reversed(str(n)))
),
0
) % 10
- ---------------------------TEST---------------------------
- main :: IO ()
def main():
Tests
print(list(
map(luhn, [
49927398716, 49927398717,
1234567812345678, 1234567812345670
])
))
if __name__ == '__main__':
main()</lang>
- Output:
[True, False, False, True]
Or alternatively, we can prune out some of the imports, define the Luhn predicate over strings rather than integers,
and cycle lambdas rather than integers.
<lang python>Luhn test of credit card numbers
from itertools import cycle
- luhn :: String -> Bool
def luhn(k):
True if k is a valid Luhn credit card number string
def asDigits(s):
return (int(c) for c in s)
return 0 == sum(map(
lambda f, x: f(x),
cycle([
lambda n: n,
lambda n: sum(asDigits(str(2 * n)))
]),
asDigits(reversed(k))
)) % 10
- ------------------------- TEST -------------------------
- main :: IO ()
def main():
Tests
print('\n'.join([
repr((x, luhn(x))) for x in [
"49927398716",
"49927398717",
"1234567812345678",
"1234567812345670"
]
]))
if __name__ == '__main__':
main()
</lang>
- Output:
('49927398716', True)
('49927398717', False)
('1234567812345678', False)
('1234567812345670', True)
Procedural
Without usingsum() and divmod() functions: <lang python>>>> def vérifLuhn(ch):
sum = 0
chParity = len(ch) % 2
for i in range (len(ch)-1, -1, -1):
j = int(ch[i])
if ((i + 1) % 2 != chParity):
j = j * 2
if (j > 9):
j = j - 9
sum = sum + j
print("value calculated = ", str(sum))
return sum % 10 == 0
for n in (49927398716, 49927398717, 1234567812345678, 1234567812345670):
print (str(n)+" =>", vérifLuhn(str(n)))
</lang>
Q
<lang q>sd:{s:0; while[x<>0; s+:x mod 10; x:floor x%10]; s} / Sum digits of x luhn:{
r:reverse string x; / Reversed credit card number
o:("I"$) each r[2*til ceiling (count r) % 2]; / Odd-indexed numbers
e:("I"$) each r[1+2*til floor (count r) % 2]; / Even-indexed numbers
0=(sum o,sd each e*2) mod 10 / Return 1b if checksum ends in 0; 0b otherwise
}</lang>
- Output:
q)luhn each 49927398716 49927398717 1234567812345678 1234567812345670 1001b
Quackery
<lang Quackery> [ 1 & ] is odd ( n --> b )
[ [] swap
[ 10 /mod
rot join swap
dup 0 = until ]
drop ] is digits ( n --> [ )
[ [] [] rot
dup size odd dip
[ witheach
[ nested join
swap ] ]
not if swap ] is unzip ( [ --> [ [ )
[ [] swap
witheach
[ 2 *
10 /mod +
join ] ] is 2*digitsum ( [ --> [ )
[ behead swap witheach + ] is sum ( [ --> n )
[ digits reverse unzip 2*digitsum sum swap sum + 10 mod 0 = ] is luhn ( n --> b )
' [ 49927398716 49927398717
1234567812345678 1234567812345670 ]
witheach
[ dup echo
luhn iff
[ say " valid" ]
else
[ say " invalid" ]
cr ]</lang>
- Output:
49927398716 valid 49927398717 invalid 1234567812345678 invalid 1234567812345670 valid
R
<lang rsplus> is.luhn <- function(cc){
numbers <- as.numeric(rev(unlist(strsplit(cc,""))))
(sum(numbers[seq(1,length(numbers),by=2)]) + sum({numbers[seq(2,length(numbers),by=2)]*2 ->.; .%%10 +.%/%10})) %% 10 == 0
}
sapply(c("49927398716","49927398717","1234567812345678","1234567812345670"),is.luhn)
</lang>
- Output:
sapply(c("49927398716","49927398717","1234567812345678","1234567812345670"),is.luhn)
49927398716 49927398717 1234567812345678 1234567812345670
TRUE FALSE FALSE TRUE
Racket
<lang Racket>
- lang racket
(define (luhn-test n)
(let loop ([n n] [odd? #t] [s 0])
(if (zero? n)
(zero? (modulo s 10))
(let*-values ([(q r) (quotient/remainder n 10)]
[(rq rr) (quotient/remainder (* (if odd? 1 2) r) 10)])
(loop q (not odd?) (+ s rq rr))))))
(map luhn-test '(49927398716 49927398717 1234567812345678 1234567812345670))
- -> '(#t #f #f #t)
</lang>
Raku
(formerly Perl 6)
Here we make use of comb, which splits into individual characters, and the sequence operator ..., which can intuit an even or odd sequence from the first two values. %% is the divisible-by operator.
<lang perl6>sub luhn-test ($number --> Bool) {
my @digits = $number.comb.reverse;
my $sum = @digits[0,2...*].sum
+ @digits[1,3...*].map({ |($_ * 2).comb }).sum;
return $sum %% 10;
}
- And we can test it like this:
use Test;
my @cc-numbers =
'49927398716' => True, '49927398717' => False, '1234567812345678' => False, '1234567812345670' => True;
plan @cc-numbers.elems;
for @cc-numbers».kv -> ($cc, $expected-result) {
is luhn-test(+$cc), $expected-result,
"$cc {$expected-result ?? 'passes' !! 'does not pass'} the Luhn test.";
}</lang>
- Output:
1..4 ok 1 - 49927398716 passes the Luhn test. ok 2 - 49927398717 does not pass the Luhn test. ok 3 - 1234567812345678 does not pass the Luhn test. ok 4 - 1234567812345670 passes the Luhn test.
REXX
version 1
<lang REXX>/*REXX program validates credit card numbers using the Luhn algorithm. */
- .=; #.1= 49927398716 /*the 1st sample credit card number. */
#.2= 49927398717 /* " 2nd " " " " */
#.3= 1234567812345678 /* " 3rd " " " " */
#.4= 1234567812345670 /* " 4th " " " " */
do k=1 while #.k\== /*validate all the credit card numbers.*/
say right( Luhn(#.k), 9) ' the Luhn test, credit card number: ' #.k
end /*k*/ /* [↑] function returns passed│flunked.*/
exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ Luhn: procedure; parse arg x; $= 0 /*get credit card number; zero $ sum. */
y= reverse( left(0, length(x) // 2)x) /*add leading zero if needed, reverse. */
do j=1 to length(y)-1 by 2; _= substr(y, j+1, 1) * 2
$= $ + substr(y, j, 1) + left(_, 1) + substr(_, 2, 1, 0) /* ◄────────┐*/
end /*j*/ /*sum odd and even decimal digits ►────┘*/
return word('passed flunked',1+($//10==0)) /*$ ending in zero? Then the # passed.*/</lang>
- output when using the (internal) default inputs:
flunked the Luhn test, credit card number: 49927398716 passed the Luhn test, credit card number: 49927398717 passed the Luhn test, credit card number: 1234567812345678 flunked the Luhn test, credit card number: 1234567812345670
Version 2
<lang REXX>/* Rexx ***************************************************
- 09.04.2013 Walter Pachl
- Implements the task's description in a rather concise way
- Instead of reverting the ccn work it backwards
- /
numeric digits 20
push 49927398716 push 49927398717 push 1234567812345678 push 1234567812345670
do while queued() > 0
parse pull ccnum if luhn(ccnum) then ln = 'passed' else ln = 'failed' say right(ccnum, 20) ln end
return exit
luhn: Parse Arg ccn /* credit card number */ sum=0 /* initialize test sum */ even=0 /* even indicator */ Do i=length(ccn) To 1 By -1 /* process all digits */
c=substr(ccn,i,1) /* pick one digit at a time */
If even Then Do /* even numbered digit */
c=c*2 /* double it */
If c>=10 Then /* 10, 12, 14, 16, 18 */
c=c-9 /* Sum of the two digits */
End /* end of even numbered */
even=\even /* flip even indicator */
sum=sum+c /* add into test sum */
End
Return right(sum,1)=0 /* ok if last digit is 0 */ </lang>
- Output:
1234567812345670 passed
1234567812345678 failed
49927398717 failed
49927398716 passed
Ring
<lang ring>decimals(0)
test = ["49927398716", "49927398717", "1234567812345678", "1234567812345670"] for n = 1 to len(test)
see test[n] + " -> " + cardtest(test[n]) + nl
next
func cardtest(numstr)
revstring = revstr(numstr)
s1 = revodd(revstring)
s2 = reveven(revstring)
s3 =right(string(s1+s2), 1)
if s3 = "0"
return "Valid"
else
return "Invalid"
ok
func revstr(str)
strnew = ""
for nr = len(str) to 1 step -1
strnew = strnew + str[nr]
next
return strnew
func revodd(str)
strnew = ""
for nr = 1 to len(str) step 2
strnew = strnew + str[nr]
next
sumodd = 0
for p = 1 to len(strnew)
sumodd = sumodd + number(strnew[p])
next
return sumodd
func reveven(str)
strnew = ""
for nr = 2 to len(str) step 2
strnew = strnew + str[nr]
next
lsteven = []
for p = 1 to len(strnew)
add(lsteven, string(2*number(strnew[p])))
next
arreven = list(len(lsteven))
for q = 1 to len(lsteven)
sum = 0
for w = 1 to len(lsteven[q])
sum = sum + lsteven[q][w]
next
arreven[q] = sum
next
sumarr = 0
for x = 1 to len(arreven)
sumarr = sumarr + arreven[x]
next
return sumarr
</lang> Output:
49927398716 -> Valid 49927398717 -> Invalid 1234567812345678 -> Invalid 1234567812345670 -> Valid
Ruby
<lang ruby> def luhn_valid?(str)
str.scan(/\d/).reverse #using str.to_i.digits fails for cases with leading zeros
.each_slice(2)
.sum { |i, k = 0| i.to_i + ((k.to_i)*2).digits.sum }
.modulo(10).zero?
end
["49927398716", "49927398717", "1234567812345678", "1234567812345670"].map{ |i| luhn_valid?(i) } </lang>
- Output:
[true, false, false, true]
Simpler Alternative <lang ruby>def luhn_valid?(n) # Card values can be numbers or strings
d2sum = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9]
sum, num = 0, n.to_i
num.digits.each_with_index { |digit, i| sum += i.even? ? digit : d2sum[digit] }
sum % 10 == 0
end
cards = [49927398716, "49927398717", 1234567812345678, "1234567812345670"] cards.each{ |i| puts "#{i}: #{luhn_valid?(i)}" }</lang>
- Output:
49927398716: true 49927398717: false 1234567812345678: false 1234567812345670: true
Run BASIC
<lang runbasic>card$(1) = "49927398716" card$(2) = "49927398717" card$(3) = "1234567812345678" card$(4) = "1234567812345670"
for i = 1 to 4 print card$(i);" ";luhn$(card$(i)) next i
FUNCTION luhn$(card$)
lc = len(card$)
for i = lc to 1 step -1
digit = val(mid$(card$,i,1))
if ((lc -i) mod 2) = 0 then chkSum = chkSum + digit else chkSum = chkSum + int(digit * 2.2)
next i
if chkSum mod 10 = 0 then luhn$ = "True" else luhn$ = "False"
end function</lang>
- Output:
49927398716 True 49927398717 False 1234567812345678 False 1234567812345670 True
Rust
<lang rust>extern crate luhn_test_of_credit_card_numbers;
use luhn_test_of_credit_card_numbers::luhn_test;
fn validate_isin(isin: &str) -> bool {
if !isin.chars().all(|x| x.is_alphanumeric()) || isin.len() != 12 {
return false;
}
if !isin[..2].chars().all(|x| x.is_alphabetic())
|| !isin[2..12].chars().all(|x| x.is_alphanumeric())
|| !isin.chars().last().unwrap().is_numeric()
{
return false;
}
let bytes = isin.as_bytes();
let s2 = bytes
.iter()
.flat_map(|&c| {
if c.is_ascii_digit() {
vec![c]
} else {
(c + 10 - ('A' as u8)).to_string().into_bytes()
}
})
.collect::<Vec<u8>>();
let string = std::str::from_utf8(&s2).unwrap(); let number = string.parse::<u64>().unwrap();
return luhn_test(number as u64);
}
- [cfg(test)]
mod tests {
use super::validate_isin;
#[test]
fn test_validate_isin() {
assert_eq!(validate_isin("US0378331005"), true);
assert_eq!(validate_isin("US0373831005"), false);
assert_eq!(validate_isin("U50378331005"), false);
assert_eq!(validate_isin("US03378331005"), false);
assert_eq!(validate_isin("AU0000XVGZA3"), true);
assert_eq!(validate_isin("AU0000VXGZA3"), true);
assert_eq!(validate_isin("FR0000988040"), true);
}
}</lang>
- Output:
49927398716: true 49927398717: false 1234567812345678: false 1234567812345670: true
Scala
Functional style
<lang scala>object Luhn {
private def parse(s: String): Seq[Int] = s.map{c =>
assert(c.isDigit)
c.asDigit
}
def checksum(digits: Seq[Int]): Int = {
digits.reverse.zipWithIndex.foldLeft(0){case (sum,(digit,i))=>
if (i%2 == 0) sum + digit
else sum + (digit*2)/10 + (digit*2)%10
} % 10
}
def validate(digits: Seq[Int]): Boolean = checksum(digits) == 0
def checksum(number: String): Int = checksum(parse(number))
def validate(number: String): Boolean = validate(parse(number))
}
object LuhnTest extends App {
Seq(("49927398716", true),
("49927398717", false),
("1234567812345678", false),
("1234567812345670", true)
).foreach { case (n, expected) =>
println(s"$n ${Luhn.validate(n)}")
assert(Luhn.validate(n) == expected)
}
}</lang>
- Output:
49927398716 true 49927398717 false 1234567812345678 false 1234567812345670 true
Imperative style
<lang scala> def luhnTest1(number: String): Boolean = {
var (odd, sum) = (true, 0)
for (int <- number.reverse.map { _.toString.toShort }) {
if (odd) sum += int
else sum += (int * 2 % 10) + (int / 5)
odd = !odd
}
sum % 10 == 0
}</lang>
Scheme
<lang scheme>(define luhn
(lambda (n)
(let loop ((number n)
(index 0)
(result 0))
(if (= 0 number)
(= 0 (remainder result 10))
(loop (quotient number 10)
(+ index 1)
(+ result
(if (even? index)
(remainder number 10)
(let ((part (* 2 (remainder number 10))))
(+ (remainder part 10) (quotient part 10))))))))))</lang>
- Output:
(map luhn '(49927398716 49927398717 1234567812345678 1234567812345670)) (#t #f #f #t)
sed
<lang sed># Split number into double evens and odds s/.*/&: /
- split
s/\([0-4]\)\([0-9]\):\(.*\) /:\1\1\3 \2/ s/\([5-9]\)\([0-9]\):\(.*\) /:1\1\1\3 \2/ t split
- Set up addition lookup table
s/\([0-9]\)*:\(.*\) \(.*\)/\1\2\3:0123456789012345678/
- add
s/\([0-9]\)0:/\1:/ s/\([0-9]\)1:\(.*\1.\{0\}\([0-9]\).*\)/\3:\2/ s/\([0-9]\)2:\(.*\1.\{1\}\([0-9]\).*\)/\3:\2/ s/\([0-9]\)3:\(.*\1.\{2\}\([0-9]\).*\)/\3:\2/ s/\([0-9]\)4:\(.*\1.\{3\}\([0-9]\).*\)/\3:\2/ s/\([0-9]\)5:\(.*\1.\{4\}\([0-9]\).*\)/\3:\2/ s/\([0-9]\)6:\(.*\1.\{5\}\([0-9]\).*\)/\3:\2/ s/\([0-9]\)7:\(.*\1.\{6\}\([0-9]\).*\)/\3:\2/ s/\([0-9]\)8:\(.*\1.\{7\}\([0-9]\).*\)/\3:\2/ s/\([0-9]\)9:\(.*\1.\{8\}\([0-9]\).*\)/\3:\2/ t add
/0:/a\ Pass /0:/!a\ Fail d</lang>
- Output:
$ sed -f luhn.sed <<! 49927398716 49927398717 1234567812345678 1234567812345670 ! Pass Fail Fail Pass
Seed7
<lang seed7>$ include "seed7_05.s7i";
const func boolean: luhnTest (in string: cardNumber) is func
result
var boolean: luhnTest is FALSE;
local
var integer: index is 0;
var integer: digit is 0;
var boolean: isOdd is TRUE;
var integer: oddSum is 0;
var integer: evenSum is 0;
begin
for index range length(cardNumber) downto 1 do
digit := integer parse str(cardNumber[index]);
if isOdd then
oddSum +:= digit;
else
evenSum +:= digit div 5 + (2 * digit) rem 10;
end if;
isOdd := not isOdd;
end for;
luhnTest := (oddSum + evenSum) rem 10 = 0;
end func;
const proc: main is func
local
var string: cardNumber is "";
begin
for cardNumber range [] ("49927398716", "49927398717", "1234567812345678", "1234567812345670") do
writeln(cardNumber <& ": " <& luhnTest(cardNumber));
end for;
end func;</lang>
- Output:
49927398716: TRUE 49927398717: FALSE 1234567812345678: FALSE 1234567812345670: TRUE
SenseTalk
<lang sensetalk>function LuhnCheck ccNum put length of ccNum into numDigits put the last character of ccNum into total put numDigits modulo 2 into parity repeat for each character of the first numDigits - 1 characters of ccNum put it into digit if (the counter - 1) modulo 2 equals parity multiply digit by 2 end if if digit is greater than 9 subtract 9 from digit end if add digit to total end repeat return total is divisible by 10 end LuhnCheck</lang>
<lang sensetalk>repeat for each item of (49927398716, 49927398717, 1234567812345678, 1234567812345670) put it && LuhnCheck(it) end repeat</lang>
SequenceL
<lang sequenceL> main(args(2)) := sum(luhnTest(asciiToInt(args[1]) - asciiToInt('0'))) mod 10 = 0;
s2Mapping := [0,2,4,6,8,1,3,5,7,9];
luhnTest(x(1))[i] := x[i] when i mod 2 = size(x) mod 2 else s2Mapping[x[i] + 1]; </lang>
Shen
<lang shen> (define mapi
_ _ [] -> [] F N [X | Xs] -> [(F N X) | (mapi F (+ N 1) Xs)])
(define double
X -> (let Y (* 2 X) (if (> Y 9) (- Y 9) Y)))
(define luhn?
Number ->
(let Exploded (explode Number)
Digits (map (/. H (- (string->n H) 48)) Exploded)
Reversed (reverse Digits)
Doubled (mapi (/. N X (if (= 1 (shen.mod N 2)) (double X) X)) 0 Reversed)
Summed (sum Doubled)
Modded (shen.mod Summed 10)
(= 0 Modded)))
"Expected: [true false false true]"
(map (function luhn?) ["49927398716" "49927398717" "1234567812345678" "1234567812345670"]) </lang>
- Output:
mapi transform-x luhn? "Expected: [true false false true]" [true false false true] run time: 0.014999985694885254 secs loaded
Sidef
<lang ruby>func luhn (n) {
static a = {|j| (2*j // 10) + (2*j % 10) }.map(^10)
var checksum = n.digits.map_kv {|i,j|
i.is_odd ? a[j] : j
}.sum
checksum % 10 == 0
}
for n in [49927398716, 49927398717, 1234567812345678, 1234567812345670] {
say [n, luhn(n)]
}</lang>
- Output:
[49927398716, true] [49927398717, false] [1234567812345678, false] [1234567812345670, true]
SNOBOL4
Using a precomputed array. <lang SNOBOL4> define('luhn(n)a,d,i,j,sum') :(luhn_end) luhn n = reverse(n); a = array('0:9') ln1 a = (2 * i / 10) + remdr(2 * i,10)
i = lt(i,9) i + 1 :s(ln1)
ln2 n len(1) . d = :f(ln3)
d = ne(remdr(j,2),0) a<d>; j = j + 1
sum = sum + d :(ln2)
ln3 luhn = 0; luhn = eq(remdr(sum,10),0) 1 :(return) luhn_end
- # Test and display
test = " output = luhn(n) ': ' n"
n = '49927398716'; eval(test)
n = '49927398717'; eval(test)
n = '1234567812345678'; eval(test)
n = '1234567812345670'; eval(test)
end</lang>
- Output:
1: 49927398716 0: 49927398717 0: 1234567812345678 1: 1234567812345670
SPARK
Works with SPARK GPL 2010 and GPS GPL 2010.
Based on the Ada version. All code shown to be free of run-time type errors.
A final test has been added which passes as valid unless there is an explicit test for all digits. <lang ada>with Spark_IO; --# inherit Spark_IO; --# main_program; procedure Luhn --# global in out Spark_IO.Outputs; --# derives Spark_IO.Outputs from *; is
function Luhn_Test (Num : String) return Boolean
--# pre Num'Last <= 20;
is
Sum : Integer := 0;
Od : Boolean := True;
Int : Integer;
X : Integer;
OK : Boolean := True;
begin
for P in reverse Integer range Num'Range loop
Int := Character'Pos(Num(P)) - Character'Pos('0');
if Int not in 0 .. 9 then
OK := False;
exit;
end if;
X := (((Int*2) mod 10) + (Int / 5));
--# assert Num'Last - P in 0 .. 19
--# and Sum in 0 .. (Num'Last - P) * 10
--# and Int in 0 .. 9
--# and X in 0 .. 10;
if Od then
Sum := Sum + Int;
else
Sum := Sum + X;
end if;
Od := not Od;
end loop;
return OK and (Sum mod 10) = 0;
end Luhn_Test;
procedure Do_Test (Num : in String)
--# global in out Spark_IO.Outputs;
--# derives Spark_IO.Outputs from *, Num;
--# pre Num'Last <= 20;
is
begin
Spark_IO.Put_String(Spark_IO.Standard_Output, Num, 16);
if Luhn_Test(Num) then
Spark_IO.Put_String(Spark_IO.Standard_Output, " is valid.", 0);
else
Spark_IO.Put_String(Spark_IO.Standard_Output, " is not valid.", 0);
end if;
Spark_IO.New_Line(Spark_IO.Standard_Output, 1);
end Do_Test;
begin
Do_Test("49927398716");
Do_Test("49927398717");
Do_Test("1234567812345678");
Do_Test("1234567812345670");
Do_Test("123456781234567D");
end Luhn;</lang>
- Output:
49927398716 is valid. 49927398717 is not valid. 1234567812345678 is not valid. 1234567812345670 is valid. 123456781234567D is not valid.
SQL PL
With SQL PL: <lang sql pl> --#SET TERMINATOR @
SET SERVEROUTPUT ON @
CREATE OR REPLACE FUNCTION LUHN_TEST (
IN NUMBER VARCHAR(24) ) RETURNS SMALLINT --) RETURNS BOOLEAN BEGIN DECLARE TYPE CARD_NUMBER AS VARCHAR(1) ARRAY [24]; DECLARE LENGTH SMALLINT; DECLARE REVERSE CARD_NUMBER; DECLARE I SMALLINT; DECLARE POS SMALLINT; DECLARE S1 SMALLINT; DECLARE S2 SMALLINT; DECLARE TEMP SMALLINT; DECLARE RET SMALLINT; --DECLARE RET BOOLEAN; DECLARE INVALID_CHAR CONDITION FOR SQLSTATE 'LUHN1';
-- Reverse the order of the digits in the number. SET LENGTH = LENGTH(NUMBER); SET I = 1; WHILE (I <= LENGTH) DO SET POS = LENGTH - I + 1; SET REVERSE[POS] = SUBSTR(NUMBER, I, 1); IF (ASCII(REVERSE[POS]) < 48 OR 57 < ASCII(REVERSE[POS])) THEN SIGNAL INVALID_CHAR SET MESSAGE_TEXT = 'Invalid character, not a digit'; END IF; SET I = I + 1; END WHILE;
-- Take the first, third, ... and every other odd digit in the reversed digits and sum them to form the partial sum s1
SET S1 = 0;
SET I = 1;
WHILE (I <= LENGTH) DO
IF (MOD(I, 2) = 1) THEN
SET S1 = S1 + REVERSE[I];
END IF;
-- CALL DBMS_OUTPUT.PUT_LINE('I ' || I || ', S1 ' || S1 || ', val ' || REVERSE[I]);
SET I = I + 1;
END WHILE;
-- Taking the second, fourth ... and every other even digit in the reversed digits:
SET S2 = 0;
SET TEMP = 0;
SET I = 1;
WHILE (I <= LENGTH) DO
IF (MOD(I, 2) = 0) THEN
-- Multiply each digit by two and sum the digits if the answer is greater than nine to form partial sums for the even digits
SET TEMP = REVERSE[I] * 2;
IF (TEMP > 9) THEN
SET TEMP = (TEMP / 10) + (MOD(TEMP, 10));
END IF;
-- Sum the partial sums of the even digits to form s2
SET S2 = S2 + TEMP;
END IF;
-- CALL DBMS_OUTPUT.PUT_LINE('I ' || I || ', S2 ' || S2 || ', TEMP ' || TEMP || ' val ' || REVERSE[I]);
SET I = I + 1;
END WHILE;
-- If s1 + s2 ends in zero then the original number is in the form of a valid credit card number as verified by the Luhn test.
SET RET = 1;
--SET RET = FALSE;
SET TEMP = S1 + S2;
IF (MOD(TEMP, 10) = 0) THEN
SET RET = 0;
--SET RET = TRUE;
CALL DBMS_OUTPUT.PUT_LINE('It is a valid number ' || S1 || '+' || S2 || '=' || TEMP);
ELSE
CALL DBMS_OUTPUT.PUT_LINE('It is NOT a valid number ' || S1 || '+' || S2 || '=' || TEMP);
END IF;
RETURN RET;
END
@ </lang> Output:
db2 -td@
db2 => SET SERVEROUTPUT ON @
DB20000I The SET SERVEROUTPUT command completed successfully.
db2 => CREATE OR REPLACE FUNCTION VALIDATE_CREDIT_CARD_NUMBER (
...
db2 (cont.) => END @
DB20000I The SQL command completed successfully.
db2 => values VALIDATE_CREDIT_CARD_NUMBER(49927398716)@
1
------
0
1 record(s) selected.
It is a valid number 42+28=70
db2 => VALUES VALIDATE_CREDIT_CARD_NUMBER(49927398717)@
1
------
1
1 record(s) selected.
It is NOT a valid number 43+28=71
db2 => VALUES VALIDATE_CREDIT_CARD_NUMBER(1234567812345678)@
1
------
1
1 record(s) selected.
It is NOT a valid number 40+28=68
db2 => VALUES VALIDATE_CREDIT_CARD_NUMBER(1234567812345670)@
1
------
0
1 record(s) selected.
It is a valid number 32+28=60
Standard ML
<lang sml>local
fun revDigits 0 = [] | revDigits n = (n mod 10) :: revDigits (n div 10)
fun digitSum n = if n > 9 then digitSum (n div 10 + n mod 10)
else n
fun luhn_sum [] = 0 | luhn_sum [d] = d | luhn_sum (d::d'::ds) = d + digitSum (2*d') + luhn_sum ds
in
fun luhn_test n = luhn_sum (revDigits n) mod 10 = 0
val res = map luhn_test [49927398716, 49927398717, 1234567812345678, 1234567812345670];
end;
(* [opening file "luhn.sml"] > val luhn_test = fn : int -> bool
val res = [true, false, false, true] : bool list
[closing file "luhn.sml"]
- )</lang>
Swift
<lang swift>func luhn(_ number: String) -> Bool {
return number.reversed().enumerated().map({
let digit = Int(String($0.element))!
let even = $0.offset % 2 == 0
return even ? digit : digit == 9 ? 9 : digit * 2 % 9
}).reduce(0, +) % 10 == 0
}
luhn("49927398716") // true luhn("49927398717") // false</lang>
Tcl
Based on an algorithmic encoding for the test on Wikipedia. <lang tcl>package require Tcl 8.5 proc luhn digitString {
if {[regexp {[^0-9]} $digitString]} {error "not a number"}
set sum 0
set flip 1
foreach ch [lreverse [split $digitString {}]] {
incr sum [lindex { {0 1 2 3 4 5 6 7 8 9} {0 2 4 6 8 1 3 5 7 9} } [expr {[incr flip] & 1}] $ch]
}
return [expr {($sum % 10) == 0}]
}</lang> Driver: <lang tcl>foreach testNumber {
49927398716 49927398717 1234567812345678 1234567812345670
} {
puts [format "%s is %s" $testNumber \
[lindex {"NOT valid" "valid"} [luhn $testNumber]]] }</lang>
- Output:
49927398716 is valid 49927398717 is NOT valid 1234567812345678 is NOT valid 1234567812345670 is valid
Terraform
<lang hcl>variable number {
type = "string"
}
locals {
digits = reverse(split("", var.number))
count = length(local.digits)
odds = [for i in range(local.count): local.digits[i] if i%2==0]
evens = [for i in range(local.count): local.digits[i] if i%2==1]
s1 = length(flatten([for d in local.odds: range(d)]))
doubles = [for d in local.evens: d * 2]
partials = [for d in local.doubles: d < 10 ? d : floor(d/10)+d%10]
s2 = length(flatten([for p in local.partials: range(p)]))
check = (local.s1 + local.s2) % 10
}
output "valid" {
value = local.check == 0
}</lang>
- Output:
$ terraform apply var.number Enter a value: 49927398716 Apply complete! Resources: 0 added, 0 changed, 0 destroyed. Outputs: valid = true $ TF_VAR_number=49927398717 terraform apply >/dev/null; terraform output valid false $ TF_VAR_number=1234567812345678 terraform apply >/dev/null; terraform output valid false $ TF_VAR_number=1234567812345670 terraform apply >/dev/null; terraform output valid true
TI-83 BASIC
<lang ti83b>PROGRAM:LUHN
- Disp "ENTER NUMBER"
- Input Str1
- 0→S
- 0→E
- For(I,length(Str1),1,-1)
:inString("0123456789",sub(Str1,I,1))–1→X
:If X<0
:Goto BA
:If E≠0
:Then
:2X→X
:If X>9
:X–9→X
:End
:X+S→S
:not(E)→E
- End
- If fPart(S/10)=0
- Then
:Disp "GOOD CARD"
- Else
:Lbl BA :Disp "BAD CARD"
- End
</lang>
Transact-SQL
<lang Transact-SQL> CREATE FUNCTION dbo._CreditCardNumCheck( @strCCNum VarChar(40) ) RETURNS VarChar(7) AS BEGIN DECLARE @string VarChar(40) = REVERSE(@strCCNum); -- usage: set once, never changed DECLARE @strS2Values VarChar(10) = '0246813579'; -- constant: maps digits to their S2 summed values DECLARE @table TABLE (ID INT, Value INT, S_Value INT); -- ID=digit position. S_Value is used for SUM(). DECLARE @p INT = 0; -- loop counter: position in string -- Convert the reversed string's digits into rows in a table variable, S_Values to be updated afterwards WHILE @p < LEN(@string) BEGIN SET @p = @p+1; INSERT INTO @table (ID,Value,S_Value) VALUES (@p, CONVERT(INT,SUBSTRING(@string,@p,1)), 0); END -- Update S_Value column : the digit's value to be summed (for even-positioned digits this is mapped via @strS2Values) UPDATE @table SET S_Value = CASE WHEN ID % 2 = 1 THEN Value ELSE CONVERT(INT,SUBSTRING(@strS2Values,Value+1,1)) END -- If the SUM of S_Values ends in 0 (modulo 10 = 0) then the CC Number is valid RETURN CASE WHEN (SELECT SUM(S_Value) FROM @table) % 10 = 0 THEN 'Valid' ELSE 'Invalid' END END </lang>
TUSCRIPT
<lang tuscript>$$ MODE TUSCRIPT MODE DATA $$ SET cardnumbers=* 49927398716 49927398717 1234567812345678 1234567812345670 $$ MODE TUSCRIPT -> collecting information for output-format SET length=MAX_LENGTH(cardnumbers) SET adjust=length+2
LOOP c=cardnumbers -> ">/" = any digit SET cstring=STRINGS (c,":>/:") SET creverse=REVERSE (cstring) SET s1=evenx2=esum=s2=""
LOOP n,oe=creverse
SET modrest=MOD(n,2)
IF (modrest==0) THEN
SET even=oe*2
IF (even>9) THEN
SET estring=STRINGS (even,":>/:")
SET esum=SUM (estring)
SET s2=APPEND (s2,esum)
ELSE
SET s2=APPEND (s2,even)
ENDIF
ELSE
SET s1=APPEND(s1,oe)
ENDIF
ENDLOOP
SET s1=SUM(s1),s2=SUM(s2) SET checksum=s1+s2 SET c=CENTER(c,-adjust) IF (checksum.ew."0") THEN
PRINT c,"true"
ELSE
PRINT c,"false"
ENDIF ENDLOOP</lang>
- Output:
49927398716 true 49927398717 false 1234567812345678 false 1234567812345670 true
TXR
<lang txr>@(do (defun luhn (num)
(for ((i 1) (sum 0))
((not (zerop num)) (zerop (mod sum 10)))
((inc i) (set num (trunc num 10)))
(let ((dig (mod num 10)))
(if (oddp i)
(inc sum dig)
(let ((dig2 (* 2 dig)))
(inc sum (+ (trunc dig2 10) (mod dig2 10)))))))))
@(collect :vars nil) @{ccnumber /[0-9]+/} @(output) @ccnumber -> @(if (luhn (int-str ccnumber 10)) "good" "bad") @(end) @(end)</lang>
$ txr luhn.txr luhn.txt 49927398716 -> good 49927398717 -> bad 1234567812345678 -> bad 1234567812345670 -> good
UNIX Shell
<lang bash>function luhn {
typeset n p s t=('0123456789' '0516273849')
while ((-n<${#1})); do
p="${t[n--%2]%${1:n:1}*}"
((s+=${#p}))
done
((s%10))
}
for c in 49927398716 49927398717 1234567812345678 1234567812345670; do
if luhn $c; then
echo $c is invalid
else
echo $c is valid
fi
done</lang>
Notes:
- The parameter expansion hack (p=${t…%${1:n:1}};…${#p}…) is an interesting way of converting a set of characters to ordinals. It's highly extensible to larger character sets (e.g. for ISBN and Code 39 checksums).
- Invalid characters are effectively treated as 0s. This is actually useful sometimes for ignoring alphabetic prefixes.
- When attempting to understand the function, remember that n is negative, so it indexes from the end of the input string.
- Output:
49927398716 is valid 49927398717 is invalid 1234567812345678 is invalid 1234567812345670 is valid
Ursala
<lang Ursala>#import std
- import nat
luhn = %nP; %np*hxiNCNCS; not remainder\10+ //sum:-0@DrlrHK32 ~&iK27K28TK25 iota10</lang>
Some notes on this solution:
iota10is the list of natural numbers<0,1,2,3,4,5,6,7,8,9>~&K27and~&K28ofiota10extract the alternate items, respectively<0,2,4,6,8>and<1,3,5,7,9>~&K27K28T iota10is their concatenation,<0,2,4,6,8,1,3,5,7,9>which is also the list of values obtained by doubling each item ofiota10and taking digit sums~&iK27K28TX iota10would be the pair(<0,1,2,3,4,5,6,7,8,9>,<0,2,4,6,8,1,3,5,7,9>), but using the reification operatorK25in place ofXmakes it an executable function taking any item of the left list as an argument and returning the corresponding item of the right.- The part beginning with
//is a function of the form//f a, which can be applied to any argumentbto obtainf(a,b). In this case, thefissum:-0@DrlrHK32, which is equivalent to the composition of two functionssum:-0and~&DrlrHK32, andais the function just obtained by reification. - The function
~&Dby itself takes a pair(a,<b0...bn>)whose right side is a list, and returns the list of pairs<(a,b0)...(a,bn)>(i.e., a copy ofapaired with eachb). Theahere will end up being the aforementioned function. ~&DrlrHK32not only forms such a list of pairs, but operates on each pair thus obtained, alternately applying~&rand~&lrHto each pair in sequence, where~&rsimply returns the right side of the pair, and~&lrHuses the left side as a function, which is applied to the right.sum:-0computes the cumulative sum of a list of natural numbers using the binarysumfunction, and the reduction operator (:-) with vacuous sum 0.- The whole thing described up to this point is therefore a function that will take a list of numbers in the range 0 to 9, and compute the summation obtained when doubling and digit summing alternate items.
- The input list to this function is constructed from a single natural number first by
%nP, which transforms it to text format in decimal, followed by%np*hxiNCNCS, which reverses the digits, makes a separate text of each, and parses them as individual numbers. - The output from the function is tested for divisibility by 10 with
remainder\10, with the result negated so that zero values map to true and non-zero to false.
usage: <lang ursala>#cast %bL
test = luhn* <49927398716,49927398717,1234567812345678,1234567812345670></lang>
- Output:
<true,false,false,true>
VBA
<lang VB> Option Explicit
Sub Main()
Debug.Print "Number 49927398716 is "; Luhn("49927398716")
Debug.Print "Number 49927398717 is "; Luhn("49927398717")
Debug.Print "Number 1234567812345678 is "; Luhn("1234567812345678")
Debug.Print "Number 1234567812345670 is "; Luhn("1234567812345670")
End Sub Private Function Luhn(Nb As String) As String Dim t$, i&, Summ&, s&
t = StrReverse(Nb)
For i = 1 To Len(t) Step 2
Summ = Summ + CInt(Mid(t, i, 1))
Next i
For i = 2 To Len(t) Step 2
s = 2 * (CInt(Mid(t, i, 1)))
If s >= 10 Then
Summ = Summ - 9
End If
Summ = Summ + s
Next i
If Summ Mod 10 = 0 Then
Luhn = "valid"
Else
Luhn = "invalid"
End If
End Function</lang>
- Output:
Number 49927398716 is valid Number 49927398717 is invalid Number 1234567812345678 is invalid Number 1234567812345670 is valid
VBScript
<lang VBScript>Function Luhn_Test(cc) cc = RevString(cc) s1 = 0 s2 = 0 For i = 1 To Len(cc) If i Mod 2 > 0 Then s1 = s1 + CInt(Mid(cc,i,1)) Else tmp = CInt(Mid(cc,i,1))*2 If tmp < 10 Then s2 = s2 + tmp Else s2 = s2 + CInt(Right(CStr(tmp),1)) + 1 End If End If Next If Right(CStr(s1 + s2),1) = "0" Then Luhn_Test = "Valid" Else Luhn_Test = "Invalid" End If End Function
Function RevString(s) For i = Len(s) To 1 Step -1 RevString = RevString & Mid(s,i,1) Next End Function
WScript.Echo "49927398716 is " & Luhn_Test("49927398716") WScript.Echo "49927398717 is " & Luhn_Test("49927398717") WScript.Echo "1234567812345678 is " & Luhn_Test("1234567812345678") WScript.Echo "1234567812345670 is " & Luhn_Test("1234567812345670")</lang>
- Output:
49927398716 is Valid 49927398717 is Invalid 1234567812345678 is Invalid 1234567812345670 is Valid
Visual Basic
<lang vb>Public Function LuhnCheckPassed(ByVal dgts As String) As Boolean Dim i As Long, s As Long, s1 As Long
dgts = VBA.StrReverse(dgts)
For i = 1 To Len(dgts) Step 2
s = s + CInt(Mid$(dgts, i, 1))
Next i
For i = 2 To Len(dgts) Step 2
s1 = 2 * (CInt(Mid$(dgts, i, 1)))
If s1 >= 10 Then
s = s - 9
End If
s = s + s1
Next i
LuhnCheckPassed = Not CBool(s Mod 10)
End Function</lang>
Test: <lang vb>Sub Main()
Debug.Assert LuhnCheckPassed("49927398716")
Debug.Assert Not LuhnCheckPassed("49927398717")
Debug.Assert Not LuhnCheckPassed("1234567812345678")
Debug.Assert LuhnCheckPassed("1234567812345670")
End Sub</lang>
Visual Basic .NET
<lang Visual Basic .NET>
Imports System.Linq
Function ValidLuhn(value As String)
Return value.Select(Function(c, i) (AscW(c) - 48) << ((value.Length - i - 1) And 1)).Sum(Function(n) If(n > 9, n - 9, n)) Mod 10 = 0
End Function
Sub Main()
Console.WriteLine(ValidLuhn("49927398716"))
Console.WriteLine(ValidLuhn("49927398717"))
Console.WriteLine(ValidLuhn("1234567812345678"))
Console.WriteLine(ValidLuhn("1234567812345670"))
End Sub
</lang>
- Output:
True False False True
Wren
<lang ecmascript>import "/fmt" for Fmt import "/trait" for Stepped
var luhn = Fn.new { |s|
// reverse digits
s = s[-1..0]
// sum the odd digits
var s1 = Stepped.new(s, 2).reduce(0) { |sum, d| sum + d.bytes[0] - 48 }
// sum two times the even digits
var s2 = Stepped.new(s[1..-1], 2).reduce(0) { |sum, d|
var d2 = (d.bytes[0] - 48) * 2
return sum + ((d2 > 9) ? d2%10 + 1 : d2)
}
// check if s1 + s2 ends in zero
return (s1 + s2)%10 == 0
}
var tests = [ "49927398716", "49927398717", "1234567812345678", "1234567812345670"] for (test in tests) {
var ans = (luhn.call(test)) ? "pass" : "fail"
System.print("%(Fmt.s(-16, test)) -> %(ans)")
}</lang>
- Output:
49927398716 -> pass 49927398717 -> fail 1234567812345678 -> fail 1234567812345670 -> pass
Xojo
<lang xojo>Public Function Modulus10(digits As String) as String
// // Confirm the digits are really, well, digits // dim validator as new RegEx validator.SearchPattern = "\A\d+\z" if validator.Search( digits ) is nil then // // Raise an exception or something // end if static doublingTable() as string = array( "0", "2", "4", "6", "8", "1", "3", "5", "7", "9" ) dim digitArr() as string = digits.Split( "" ) for i as integer = digitArr.Ubound downto 0 step 2 digitArr( i ) = doublingTable( digitArr( i ).Val ) next dim sum as integer for each digit as string in digitArr sum = sum + digit.Val next dim check as integer = ( sum * 9 ) mod 10 return str( check )
End Function
Public Function ValidateMod10(digits As String) as Boolean
dim checkDigit as string = digits.Right( 1 ) digits = digits.Left( digits.Len - 1 ) return Modulus10( digits ) = checkDigit
End Function </lang>
- Output:
ValididateMod10( "49927398716" ) = True ValididateMod10( "49927398717" ) = False ValididateMod10( "1234567812345678" ) = False ValididateMod10( "1234567812345670" ) = True
XPL0
<lang XPL0>string 0; \use zero-terminated strings
func Valid(Str); \Return 'true' if digits in Str pass Luhn test char Str; int Len, Sum, I, Dig; [Len:= 0; \find length of Str while Str(Len) do Len:= Len+1; Sum:= 0; \sum even and odd digits for I:= 0 to Len-1 do \(no need to reverse)
[if (I xor Len) and 1 then
Sum:= Sum + Str(I) - ^0
else [Dig:= Str(I) - ^0;
Dig:= Dig*2;
Sum:= Sum + Dig/10 + rem(0);
];
];
return rem(Sum/10) = 0; ];
int Luhn, N; [Luhn:= ["49927398716",
"49927398717",
"1234567812345678",
"1234567812345670"];
for N:= 0 to 4-1 do
[Text(0, Luhn(N));
Text(0, if Valid(Luhn(N))
then " is valid"
else " is not valid");
CrLf(0);
];
]</lang>
- Output:
49927398716 is valid 49927398717 is not valid 1234567812345678 is not valid 1234567812345670 is valid
zkl
<lang zkl>fcn luhnTest(n){
0 == (n.split().reverse().reduce(fcn(s,n,clk){
s + if(clk.next()) n else 2*n%10 + n/5 },0,Walker.cycle(1,0)) %10)
}</lang> <lang zkl>T(49927398716,49927398717,1234567812345678,1234567812345670) .apply(luhnTest).println();</lang>
- Output:
L(True,False,False,True)
ZX Spectrum Basic
<lang ZXBasic>10 LET c$="49927398716": GO SUB 1000 20 LET c$="49927398717": GO SUB 1000 30 LET c$="1234567812345678": GO SUB 1000 40 LET c$="1234567812345670": GO SUB 1000 999 STOP 1000 REM ************* 1001 REM * LUHN TEST * 1002 REM ************* 1010 LET r$="" 1020 FOR i=LEN c$ TO 1 STEP -1 1030 LET r$=r$+c$(i) 1040 NEXT i 1050 LET s1=0: LET s2=0 1060 FOR i=1 TO LEN r$ STEP 2 1070 LET s1=s1+VAL r$(i) 1080 NEXT i 1090 FOR i=2 TO LEN r$ STEP 2 1100 LET s2sub=VAL r$(i)*2 1110 IF s2sub>=10 THEN LET s2sub=1+s2sub-10 1120 LET s2=s2+s2sub 1130 NEXT i 1140 LET s$=STR$ (s1+s2) 1150 IF s$(LEN s$)="0" THEN PRINT c$;" VALID!": LET retval=1: RETURN 1160 PRINT c$;" INVALID!": LET retval=0: RETURN </lang>
- Output:
49927398716 VALID! 49927398717 INVALID! 1234567812345678 INVALID! 1234567812345670 VALID!