Generalised floating point addition is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

It is possible to implement floating point arithmetic in many different ways; though the standard IEEE arithmetic implementation on modern hardware usually uses a fixed-width binary implementation (using a total of 32 bits for single-precision floats — `float` in a number of languages — and 64 bits for double-precision floats — `double`) many other schemes can be used. For example, the base need not be binary (alternatives include decimal, binary-coded decimal, and even balanced ternary) and there is no requirement that a fixed number of digits be used.

Define addition for floating point numbers where the digits are stored in an arbitrary base; e.g. the digits can be stored as binary, decimal, binary-coded decimal, or even balanced ternary. You should implement the code in a generalised form (such as a Template, Module or Mixin etc) that permits reusing of the code for different Bases.

If it is not possible to implement code by providing an implementation that uses the syntax of the specific language then:

• Note the reason why this is.
• Demonstrate that the language still supports the semantics of generalised floating point by implementing the test case using built-in code or a library.

Test case:

Define arbitrary precision addition on floating point numbers (e.g., encoding those numbers using Binary Coded Decimal, or using an arbitrary precision integer arithmetic library). Calculate the terms for -7 to 21 in this sequence of calculations:

Calculate the terms for -7 to 21 in this sequence of calculations
Number Term calculation Result
-7 12345679e63 × 81 + 1e63 1e72
-6 12345679012345679e54 × 81 + 1e54 1e72
-5 12345679012345679012345679e45 × 81 + 1e45 1e72
-4 12345679012345679012345679012345679e36 × 81 + 1e36 1e72
etc. The final calculation will be over 256 digits wide 1e72

You will either need to implement multiplication, or perform the multiplication by 81 by using repeated additions. The results will always be 1e72.

Bonus

Make the template (module, class, mixing, etc.) able to successfully handle using other bases to perform the above test case. Demonstrate using balanced ternary.

## ALGOL 68

Works with: ALGOL 68 version Revision 1 - one minor extension to language used - PRAGMA READ, similar to C's #include directive.
Works with: ALGOL 68G version Any - tested with release algol68g-2.3.3.

Note: This code stores the digits as array of digits with the "most significant digit" on the "left" as per normal "human" form. The net effect is that whole numbers (such as 100) are stored in the negative array positions, eg -2, -1 & 0, or [-2:0], And the fractional part of the floating point numbers are stored from index 1, eg. 1, 2, 3 etc. or [1:].

```########################################
#  Define the basic addition operators #
#  for the generalised base            #
########################################

# derived DIGIT operators #
OP + = (DIGIT arg)DIGIT: arg;
OP + = (DIGIT a,b)DIGIT: (DIGIT out := a; MOID(out +:= b); out);

# derived hybrid of DIGIT & DIGITS operators #
OP + = (DIGITS a, DIGIT b)DIGITS: a + INITDIGITS b;
OP + = (DIGIT a, DIGITS b)DIGITS: INITDIGITS a + a;
OP +:= = (REF DIGITS lhs, DIGIT arg)DIGITS: lhs := lhs + arg;

# derived DIGITS operators #
OP + = (DIGITS arg)DIGITS: arg;
OP +:= = (REF DIGITS lhs, DIGITS arg)DIGITS: lhs := lhs + arg;

####################################
# Actual generic addition operator #
####################################
OP + = (DIGITS a, b)DIGITS: (
IF SIGN a = 0 THEN b ELIF SIGN b = 0 THEN a
ELSE
MODE SIGNED = DIGIT;

INT extreme highest = MSD a MIN MSD b,
overlap highest = MSD a MAX MSD b,
overlap lowest  = LSD a MIN LSD b,
extreme lowest  = LSD a MAX LSD b;

SIGNED zero = ZERO LOC SIGNED;
INT order = digit order OF arithmetic;
DIGITS out;

IF overlap highest > overlap lowest THEN # Either: NO overlapping digits #

[extreme highest:extreme lowest]SIGNED a plus b;

# First: simply insert the known digits with their correct sign #
a plus b[MSD a:LSD a] := a[@1];
a plus b[MSD b:LSD b] := b[@1];

# Next: Zero any totally non overlapping digit #
FOR place FROM overlap highest+order BY order TO overlap lowest-order
DO a plus b[place] := zero OD;

# Finally: normalise by removing leading & trailing "zero" digit #
out := INITDIGITS a plus b

ELSE # Or: Add ALL overlapping digits #

[extreme highest+(carry OF arithmetic|order|0):extreme lowest]SIGNED a plus b;

#   First: Deal with the non overlapping Least Significant Digits #
a plus b[overlap lowest-order:] := (LSD a > LSD b|a|b) [overlap lowest-order:];

#   Or: Add any overlapping digits #
SIGNED carry := zero;
FOR place FROM overlap lowest BY order TO overlap highest DO
SIGNED digit a = a[place], digit b = b[place];
REF SIGNED result = a plus b[place];
IF carry OF arithmetic THEN # used in big float #
result := carry;
carry := ( result +:= digit a );
MOID( carry +:= ( result +:= (digit b) ) )
ELSE
result  := digit a;
MOID( result +:= digit b )
FI
OD;

#   Next: Deal with the non overlapping Most Significant digits #
FOR place FROM overlap highest+order BY order TO extreme highest DO
[]DIGIT etc = (MSD a < MSD b|a|b);
REF SIGNED result = a plus b[place];
IF carry OF arithmetic THEN
result := carry;
carry := ( result +:= etc[place] )
ELSE
result := etc[place]
FI
OD;

#   Next: Deal with the carry #
IF carry OF arithmetic THEN
a plus b[extreme highest+order] := carry
FI;

#   Finally: normalise by removing leading & trailing "zero" digits #
out := INITDIGITS a plus b

FI;
out # EXIT #
FI
);```

File: Template.Big_float.Base.a68 - task utility code

```# -*- coding: utf-8 -*- #
################################################
#  Define the basic operators and routines for #
#  manipulating DIGITS in a generalised base   #
################################################

STRUCT (
BOOL balanced,
carry, # aka "carry" between digits #
INT base,
digit width,
digit places,
digit order,
USTRING repr
) arithmetic := (
FALSE, TRUE,
10, 1, 81, -1, # Default is BCD/Hex #
USTRING( # Note that the "circled" digits are negative - used in balance arithmetic #
"ⓩ","ⓨ","ⓧ","ⓦ","ⓥ","ⓤ","ⓣ","ⓢ","ⓡ","ⓠ","ⓟ","ⓞ","ⓝ","ⓜ","ⓛ","ⓚ","ⓙ","ⓘ","ⓗ","ⓖ","ⓕ","ⓔ","ⓓ","ⓒ","ⓑ","ⓐ",
"Ⓩ","Ⓨ","Ⓧ","Ⓦ","Ⓥ","Ⓤ","Ⓣ","Ⓢ","Ⓡ","Ⓠ","Ⓟ","Ⓞ","Ⓝ","Ⓜ","Ⓛ","Ⓚ","Ⓙ","Ⓘ","Ⓗ","Ⓖ","Ⓕ","Ⓔ","Ⓓ","Ⓒ","Ⓑ","Ⓐ",
"⑨","⑧","⑦","⑥","⑤","④","③","②","①",    "0",    "1","2","3","4","5","6","7","8","9",
"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z",
"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"
)[@-(26*2+9)] # can print up to base 61, or balanced base 123 #
);

MODE DIGITS = FLEX[0]DIGIT;

# DIGIT OPerators #
OP INITDIGIT = (#LONG# INT i)DIGIT: (DIGIT out; digit OF out := #SHORTEN# i; out);
#OP INITDIGIT = (INT i)DIGIT: INITDIGIT LENG i;#

OP /= = (DIGIT a,b)BOOL: digit OF a /= digit OF b;

# Define additive and multiplicative identities #
OP ZERO = (DIGITS skip)DIGITS: INITDIGITS []DIGIT(ZERO LOC DIGIT),
IDENTITY = (DIGITS skip)DIGITS: INITDIGITS []DIGIT(IDENTITY LOC DIGIT);

OP SIGN = (DIGIT digit)INT: SIGN digit OF digit;

# Define OPerators for Least and Most Significant DIGIT #
OP MSD = (DIGITS t)INT: LWB t,
EXP = (DIGITS t)INT: digit order OF arithmetic * LWB t, # exponent #
LSD = (DIGITS t)INT: UPB t;

OP INITDIGITS = (DIGIT in)DIGITS: INITDIGITS []DIGIT(in)[@0];

OP INITDIGITS = ([]DIGIT digits)DIGITS: (
### normalise digits:
A) removed leading & trailing zeros
B) IF not balanced arithmetic
THEN make all digits positive and set sign bit FI
###
MODE SIGNED = DIGIT;
DIGIT zero = ZERO LOC DIGIT;
DIGIT one = IDENTITY LOC DIGIT;
DIGIT base digit = INITDIGIT base OF arithmetic;
INT base = base OF arithmetic;
INT half base = base % 2;
INT order = digit order OF arithmetic;

INT msd := LWB digits + int width*order, lsd := UPB digits; # XXX #

# create an array with some "extra" significant digits incase there is a "big" input value #
[msd:lsd]SIGNED signed; signed[LWB digits:UPB digits] := digits[@1];
FOR place FROM LWB signed TO LWB digits+order DO
signed[place] := zero
OD;
IF msd + order /= lsd THEN

FOR place FROM msd BY -order TO lsd DO
IF SIGN signed[place] /= 0 THEN msd := place; done msd FI
OD;
msd := lsd-order;
done msd:
#   Trim trailing zeros #
FOR place FROM lsd BY order TO msd DO
IF SIGN signed[place] /= 0 THEN lsd := place; done lsd FI
OD;
lsd := msd+order;
done lsd:
IF msd + order /= lsd THEN  # not zero #
IF carry OF arithmetic THEN # Normalise to the "base OF arithmetic": #
INT sign msd := SIGN digits[msd]; # first non zero digit #
INT lwb digit := (balanced OF arithmetic|-half base|:sign msd < 0 |1-base|0);
INT upb digit := (balanced OF arithmetic| half base|:sign msd > 0 |base-1|0);
SIGNED carry := zero;
FOR place FROM lsd BY order WHILE SIGN carry /=0 OR place >= LWB digits DO
SIGNED digit := signed[place];
carry := digit +:= carry;
WHILE digit OF digit < lwb digit DO
MOID(digit +:= base digit);
MOID(carry -:= one)
OD;
WHILE digit OF digit > upb digit DO
MOID(digit -:= base digit);
MOID(carry +:= one)
OD;
signed[place] := digit; # normalised #
IF SIGN digit /= 0 THEN msd := place FI
OD
FI
FI;
signed[msd:lsd][@msd]
FI
);

# re anchor the array with a shift #
OP SHL = (DIGITS in, INT shl)DIGITS: in[@MSD in-shl];
OP SHR = (DIGITS in, INT shr)DIGITS: in[@MSD in+shr];```

File: Template.Big_float_BCD.Base.a68 - test case code

```################################################
#  Define the basic operators and routines for #
#  manipulating DIGITS specific to a BCD base  #
################################################

####################################################
# BCD noramlly means Binary Coded Decimal, but...  #
# this code handles "Balanced Coded Data", meaning #
# Data can be in any numerical bases, and the data #
# can optionally be stored as Balanced about zero  #
####################################################

# define the basic axioms of the number system you are extending #
MODE DIGIT = STRUCT(#LONG# INT digit);
# Note: If the +:= and *:= operators for INT are being "overloaded",
then it is sometimes necessary to wrap an INT in a STRUCT to
protect the builtin definitions of the INT OPerators
#

# mixin the Big_float base definitions #

MODE BIGREAL  = DIGITS;

# the Yoneda ambiguity forces the peculiar coercion n the body of OP #
OP ZERO = (DIGIT skip)DIGIT: (DIGIT out; digit OF out := 0; out);
OP IDENTITY = (DIGIT skip)DIGIT: (DIGIT out; digit OF out := 1; out);

# define the basis operators #
OP ABS = (DIGIT a)INT: ABS digit OF a;
OP - = (DIGIT a)DIGIT: INITDIGIT -digit OF a;

####################################################################
# Important: Operator +:= is required by Template_Big_float_addition. #
####################################################################
# Note: +:= returns carry DIGIT #
OP +:= = (REF DIGIT lhs, DIGIT arg)DIGIT: (
# Todo: Implement balanced arithmetic #
INT sum = digit OF lhs + digit OF arg;   # arg may be -ve #
INT carry := sum % base OF arithmetic;
INT digit := sum - carry * base OF arithmetic;
IF balanced OF arithmetic THEN
INT half base = base OF arithmetic OVER 2;
IF   digit > half base THEN
digit -:= base OF arithmetic;
carry +:= 1
ELIF digit < -half base THEN
digit +:= base OF arithmetic;
carry -:= 1
FI
FI;
lhs := INITDIGIT digit; INITDIGIT carry
);

INT half = base OF arithmetic OVER 2;
# ASSERT NOT balanced OF arithmetic OR ODD base OF arithmetic #
##########################################################################
# Important: Operator *:= is required by Template_Big_float_multiplication. #
##########################################################################
# Note: *:= returns carry DIGIT #

OP *:= = (REF DIGIT lhs, DIGIT arg)DIGIT: (
# Todo: Implement balanced arithmetic #
INT product = digit OF lhs * digit OF arg;   # arg may be -ve #
INT carry = product % base OF arithmetic;
lhs := INITDIGIT(product - carry * base OF arithmetic);
INITDIGIT carry
);

##########################################################
# Define the basic coersion/casting rules between types. #
##########################################################
OP INITLONGREAL = (BIGREAL a)LONG REAL:
IF SIGN a = 0 THEN 0
ELSE
INT lsd a = LSD a; # Todo: Optimise/reduce to match "long real width" #
LONG REAL out := digit OF a[MSD a];
FOR place FROM MSD a - digit order OF arithmetic BY -digit order OF arithmetic TO lsd a DO
out := out * base OF arithmetic + digit OF a[place]
OD;
out * LONG REAL(base OF arithmetic) ** -LSD a
FI;

OP INITREAL = (BIGREAL r)REAL:
SHORTEN INITLONGREAL r;

OP MSD = (LONG INT i)INT: (
LONG INT remainder := i; INT count := 0;
WHILE remainder /= 0 DO
remainder %:= base OF arithmetic;
MOID(count +:= 1)
OD;
count
);

OP INITBIGREAL = (LONG INT in int)BIGREAL: (

INT max = MSD in int;
[1-max:0]DIGIT out;

LONG INT int := ABS in int;

FOR place FROM UPB out BY digit order OF arithmetic TO LWB out WHILE int /= 0 DO
INT digit := SHORTEN (int MOD base OF arithmetic);
int := (int-digit) OVER base OF arithmetic;
(digit OF out)[place] := sign * digit
OD;
done:
INITDIGITS out # normalise #
);

OP INITBIGREAL = (INT in int)BIGREAL:
INITBIGREAL LENG in int;

OP INITBIGREAL = (LONG REAL in real)BIGREAL: (

LONG REAL real := ABS in real;
LONG REAL frac := real - ENTIER real;
BIGREAL whole = INITBIGREAL ENTIER real; # normalised #

INT base = base OF arithmetic,
order = digit order OF arithmetic,
lsd = digit places OF arithmetic; # Todo: can be optimised/reduced #

[MSD whole:lsd]DIGIT out; out[MSD whole:LSD whole] := whole[@1];
FOR place FROM LSD whole - order TO 0 DO out[place] := INITDIGIT 0 OD; # pad #

FOR place FROM -order BY -order TO lsd DO
frac *:= base;
#LONG# INT digit := SHORTEN ENTIER frac;
frac -:= digit;
(digit OF out)[place] := digit;
IF frac = 0 THEN done FI
OD;
done:
IF sign > 1 THEN INITDIGITS out ELSE - INITDIGITS out FI
);

OP INITBIGREAL = (REAL in real)BIGREAL:
INITBIGREAL LENG in real;

#FORMAT digit fmt = \$n(digit width OF arithmetic+ABS balanced OF arithmetic)(d)\$;#
FORMAT big real fmt = \$g((digit width OF arithmetic+ABS balanced OF arithmetic))","\$;

OP REPR = (DIGIT digit)STRING:
IF LWB repr OF arithmetic <= digit OF digit AND digit OF digit <= UPB repr OF arithmetic THEN
(repr OF arithmetic)[digit OF digit]
ELIF balanced OF arithmetic THEN
whole(digit OF digit,digit width OF arithmetic+1)
ELSE
whole(digit OF digit,-digit width OF arithmetic)
FI;

OP REPR = (BIGREAL real)STRING:(
CHAR repr 0 = "0";
STRING out;
FOR place FROM MSD real BY -digit order OF arithmetic TO LSD real DO
IF place = 1 AND place =  MSD real THEN out +:= "." FI;
out +:= REPR(real[place]);
IF place = 0 AND place /=  LSD real THEN out +:= "." FI
OD;
IF out = "" THEN out := repr 0 FI;
IF SIGN real < 0 AND NOT balanced OF arithmetic THEN "-" +=: out FI;
IF MSD real > 1 AND LSD real > 1 OR
MSD real < 0 AND LSD real < 0 THEN
# No decimal point yet, so maybe we need to add an exponent #
out+IF digit order OF arithmetic*LSD real = 1 THEN repr 0
ELSE "e"+REPR INITBIGREAL(digit order OF arithmetic*LSD real) FI
# ELSE "E"+whole(digit order OF arithmetic*LSD real,0) FI #
ELSE
out
FI
);```

File: Template.Big_float.Subtraction.a68 - bonus subtraction definitions

```OP - = (DIGITS arg)DIGITS: (
DIGITS out := arg;
FOR digit FROM LSD arg BY digit order OF arithmetic TO MSD arg DO
out[digit]:= -out[digit]
OD;
out
);

OP SIGN = (DIGITS arg)INT:
IF LSD arg - MSD arg  = digit order OF arithmetic THEN 0 # empty array #
ELSE # balanced artihmetic # SIGN arg[MSD arg] FI;

OP ABS = (DIGITS arg)DIGITS:
IF SIGN arg < 0 THEN -arg ELSE arg FI;

# derived DIGIT operators #
OP - = (DIGIT a, b)DIGIT: a + -b;
OP -:= = (REF DIGIT a, DIGIT b)DIGIT: a := a + -b;

# derived DIGITS operators #
OP - = (DIGITS a, b)DIGITS: a + -b;
OP -:= = (REF DIGITS a, DIGITS b)DIGITS: a := a + -b;

# derived hybrid DIGIT and DIGITS operators #
OP - = (DIGITS a, DIGIT b)DIGITS: a - INITDIGITS b;
OP - = (DIGIT a, DIGITS b)DIGITS: INITDIGITS a - a;
OP -:= = (REF DIGITS lhs, DIGIT arg)DIGITS: lhs := lhs - arg;```

File: test.Big_float_BCD.Addition.a68 - test case code main program

```#!/usr/local/bin/a68g --script #

##################################################################
#                        TEST CASE                               #
# A program to test abritary length BCD floating point addition. #
##################################################################

PR READ "prelude/general.a68" PR # [[rc:Template:ALGOL 68/prelude]] #

##################################################################
##################################################################

# include the basic axioms of the digits being used #

test: (
BIGREAL pattern = INITBIGREAL 012345679,
INT pattern width = 9;

BIGREAL
sum := INITBIGREAL 0,
shifted pattern := pattern,
shifted tiny := INITBIGREAL 1; # typically 0.000.....00001 etc #

FOR term FROM -8 TO 20 DO

# First make shifted pattern smaller by shifting right by the pattern width #
shifted pattern := (shifted pattern)[@term*pattern width+2];
shifted tiny := (shifted tiny)[@(term+1)*pattern width];

MOID(sum +:= shifted pattern);

# Manually multiply by 81 by repeated addition #
BIGREAL prod := sum + sum + sum;
MOID(prod +:= prod + prod);
MOID(prod +:= prod + prod);
MOID(prod +:= prod + prod);

BIGREAL total = prod + shifted tiny;

IF term < -4 THEN
print(( REPR sum," x 81 gives: ", REPR prod, ", Plus ",REPR shifted tiny," gives: "))
ELSE
print((LSD prod - MSD prod + 1," digit test result: "))
FI;
printf((\$g\$, REPR total, \$" => "b("Passed","Failed")"!"\$, LSD total = MSD total, \$l\$))
OD
)```

Output:

```12345679e63 x 81 gives: 999999999e63, Plus 1e63 gives: 1e72 => Passed!
12345679012345679e54 x 81 gives: 999999999999999999e54, Plus 1e54 gives: 1e72 => Passed!
12345679012345679012345679e45 x 81 gives: 999999999999999999999999999e45, Plus 1e45 gives: 1e72 => Passed!
12345679012345679012345679012345679e36 x 81 gives: 999999999999999999999999999999999999e36, Plus 1e36 gives: 1e72 => Passed!
+45 digit test result: 1e72 => Passed!
+54 digit test result: 1e72 => Passed!
+63 digit test result: 1e72 => Passed!
+72 digit test result: 1e72 => Passed!
+81 digit test result: 1e72 => Passed!
+90 digit test result: 1e72 => Passed!
+99 digit test result: 1e72 => Passed!
+108 digit test result: 1e72 => Passed!
+117 digit test result: 1e72 => Passed!
+126 digit test result: 1e72 => Passed!
+135 digit test result: 1e72 => Passed!
+144 digit test result: 1e72 => Passed!
+153 digit test result: 1e72 => Passed!
+162 digit test result: 1e72 => Passed!
+171 digit test result: 1e72 => Passed!
+180 digit test result: 1e72 => Passed!
+189 digit test result: 1e72 => Passed!
+198 digit test result: 1e72 => Passed!
+207 digit test result: 1e72 => Passed!
+216 digit test result: 1e72 => Passed!
+225 digit test result: 1e72 => Passed!
+234 digit test result: 1e72 => Passed!
+243 digit test result: 1e72 => Passed!
+252 digit test result: 1e72 => Passed!
+261 digit test result: 1e72 => Passed!
```

## Go

Although the big.Float type already has a 'Mul' method, we re-implement it by repeated application of the 'Add' method.

```package main

import (
"fmt"
"math/big"
)

func repeatedAdd(bf *big.Float, times int) *big.Float {
if times < 2 {
return bf
}
var sum big.Float
for i := 0; i < times; i++ {
}
return &sum
}

func main() {
s := "12345679"
t := "123456790"
e := 63
var bf, extra big.Float
for n := -7; n <= 21; n++ {
bf.SetString(fmt.Sprintf("%se%d", s, e))
extra.SetString(fmt.Sprintf("1e%d", e))
fmt.Printf("%2d : %s\n", n, bf.String())
s = t + s
e -= 9
}
}
```
Output:
```-7 : 1e+72
-6 : 1e+72
-5 : 1e+72
-4 : 1e+72
-3 : 1e+72
-2 : 1e+72
-1 : 1e+72
0 : 1e+72
1 : 1e+72
2 : 1e+72
3 : 1e+72
4 : 1e+72
5 : 1e+72
6 : 1e+72
7 : 1e+72
8 : 1e+72
9 : 1e+72
10 : 1e+72
11 : 1e+72
12 : 1e+72
13 : 1e+72
14 : 1e+72
15 : 1e+72
16 : 1e+72
17 : 1e+72
18 : 1e+72
19 : 1e+72
20 : 1e+72
21 : 1e+72
```

## J

I am not currently able to implement the task exactly because I do not quite understand what is being asked for (nor why it would be useful).

That said, the task does specify some calculations to be performed.

Given

```e=: 2 : 0
u * 10x ^ v
)
```

In other words, given a parse time word (`e`) which combines its two arguments as numbers, multiplying the number on its left by the exact exponent of 10 given on the right, I can do:

```   1 e 63 + 12345679 e 63 * 81
1000000000000000000000000000000000000000000000000000000000000000000000000
1 e 54 + 12345679012345679 e 54 * 81
1000000000000000000000000000000000000000000000000000000000000000000000000
1 e 45 + 12345679012345679012345679x e 45 * 81
1000000000000000000000000000000000000000000000000000000000000000000000000
1 e 36 + 12345679012345679012345679012345679x e 36 * 81
1000000000000000000000000000000000000000000000000000000000000000000000000
```

As usual, if the results seem mysterious, it can be helpful to examine intermediate results. For example:

```   1 e 36 ,: 12345679012345679012345679012345679x e 36 * 81
1000000000000000000000000000000000000
999999999999999999999999999999999999000000000000000000000000000000000000
```

So, ok, let's turn this into a sequence:

```factor=: [: +/ [: 12345679 e ] _9 * 1 + i.&.(+&8)
```

Here we show some examples of what these words mean:

```   factor _4  NB. this is the number we multiply by 81
12345679012345679012345679012345679000000000000000000000000000000000000
factor _3
12345679012345679012345679012345679012345679000000000000000000000000000
factor 2 NB. here we see that we are using rational numbers
12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679r1000000000000000000
90j18 ":  factor 2  NB. formatted as decimal in 90 characters with 18 characters after the decimal point
12345679012345679012345679012345679012345679012345679012345679012345679.012345679012345679
adjust _4  NB. this is the number we add to the result of multiplying our factor by 81
1000000000000000000000000000000000000
1000000000000000000000000000
```

Given these words:

```   _7+i.29 NB. these are the sequence elements we are going to generate
_7 _6 _5 _4 _3 _2 _1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
#(adju + 81 * factor)&> _7+i.29 NB. we generate a sequence of 29 numbers
29
~.(adju + 81 * factor)&> _7+i.29  NB. here we see that they are all the same number
1000000000000000000000000000000000000000000000000000000000000000000000000
```

Note that `~. list` returns the unique elements from that list.

## Java

Java provides a `BigDecimal` class that supports robust arbitrary precision calculations. That class is demonstrated using the computations required in this task.

```import java.math.BigDecimal;

public static void main(String[] args) {
BigDecimal oneExp72 = new BigDecimal("1E72");
for ( int i = 0 ; i <= 21+7 ; i++ ) {
String s = "12345679";
for ( int j = 0 ; j < i ; j++ ) {
s += "012345679";
}
int exp = 63 - 9*i;
s += "E" + exp;
BigDecimal num = new BigDecimal(s).multiply(BigDecimal.valueOf(81)).add(new BigDecimal("1E" + exp));
System.out.printf("Test value (%s) equals computed value: %b.  Computed = %s%n", oneExp72, num.compareTo(oneExp72) == 0 , num);
}
}

}
```
Output:
```Test value (1E+72) equals computed value: true.  Computed = 1.000000000E+72
Test value (1E+72) equals computed value: true.  Computed = 1.000000000000000000E+72
Test value (1E+72) equals computed value: true.  Computed = 1.000000000000000000000000000E+72
Test value (1E+72) equals computed value: true.  Computed = 1.000000000000000000000000000000000000E+72
Test value (1E+72) equals computed value: true.  Computed = 1.000000000000000000000000000000000000000000000E+72
Test value (1E+72) equals computed value: true.  Computed = 1.000000000000000000000000000000000000000000000000000000E+72
Test value (1E+72) equals computed value: true.  Computed = 1.000000000000000000000000000000000000000000000000000000000000000E+72
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Test value (1E+72) equals computed value: true.  Computed = 1000000000000000000000000000000000000000000000000000000000000000000000000.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
```

## Julia

Julia implements arbitary precision intergers and floating point numbers in its base function.

```@assert(big"12345679e63" * BigFloat(81) + big"1e63" == big"1.0e+72")
@assert(big"12345679012345679e54" * BigFloat(81) + big"1e54" == big"1.0e+72")
@assert(big"12345679012345679012345679e45" * BigFloat(81) + big"1e45" == big"1.0e+72")
@assert(big"12345679012345679012345679012345679e36" * BigFloat(81) + big"1e36" == big"1.0e+72")
```

All assertions pass.

## Kotlin

The JDK has an arbitrary precision BigDecimal class which uses a scaled decimal representation internally. This enables decimal numbers of any size to be represented exactly.

Although the BigDecimal type supports multiplication, I've used repeated addition here to be more in tune with the spirit of the task.

```// version 1.2.10

import java.math.BigDecimal

var sum = BigDecimal.ZERO
for (i in 0 until times) sum += this
return sum
}

fun main(args: Array<String>) {
var s = "12345679"
val t = "123456790"
var e = 63
for (n in -7..21) {
val bd = BigDecimal("\${s}e\$e")
val oneE = BigDecimal("1e\$e")
val result = temp.repeatedAdd(9) + oneE
println("%2d : %e".format(n, result))
s = t + s
e -= 9
}
}
```
Output:
```-7 : 1.000000e+72
-6 : 1.000000e+72
-5 : 1.000000e+72
-4 : 1.000000e+72
-3 : 1.000000e+72
-2 : 1.000000e+72
-1 : 1.000000e+72
0 : 1.000000e+72
1 : 1.000000e+72
2 : 1.000000e+72
3 : 1.000000e+72
4 : 1.000000e+72
5 : 1.000000e+72
6 : 1.000000e+72
7 : 1.000000e+72
8 : 1.000000e+72
9 : 1.000000e+72
10 : 1.000000e+72
11 : 1.000000e+72
12 : 1.000000e+72
13 : 1.000000e+72
14 : 1.000000e+72
15 : 1.000000e+72
16 : 1.000000e+72
17 : 1.000000e+72
18 : 1.000000e+72
19 : 1.000000e+72
20 : 1.000000e+72
21 : 1.000000e+72
```

## Perl

Calculations done in decimal, prints 'Y' for each successful test.

```use strict;
use warnings;

my \$e = 63;
for my \$n (-7..21) {
my \$num = '12345679' . '012345679' x (\$n+7);
my \$sum = dec_mul_pow10(1, \$e);
\$sum = dec_add(\$sum, dec_mul_pow10(\$num,\$e)) for 1..81;
printf "\$n:%s ", 10**72 == \$sum ? 'Y' : 'N';
\$e -= 9;
}
```
Output:
```-7:Y -6:Y -5:Y -4:Y -3:Y -2:Y -1:Y 0:Y 1:Y 2:Y 3:Y 4:Y 5:Y 6:Y 7:Y 8:Y 9:Y 10:Y 11:Y 12:Y 13:Y 14:Y 15:Y 16:Y 17:Y 18:Y 19:Y 20:Y 21:Y
```

## Phix

### bigatom

Note this is decimal-only, and that mpfr.e does not really cope because it cannot hold decimal fractions exactly (though it could probably be fudged with a smidgen of rounding)

```include bigatom.e
{} = ba_scale(200)

string s = "12345679",
t = "123456790"
integer e = 63
for n = -7 to 21 do
bigatom bd = ba_new(sprintf("%se%d",{s,e})),
e1 = ba_new(sprintf("1e%d",e)),
--          res = ba_mul(bd,81)
printf(1,"%2d : %s\n",{n,ba_sprintf("%.eB",res)})
--  printf(1,"%2d : %s\n",{n,ba_sprintf("%B",res)})
s = t & s
e -= 9
end for
```
Output (trimmed):

(Use the %B format to better see the difference between adding and not adding e1.)

```-7 : 1e72
...
21 : 1e72
```

### any base

Uses b_add() and b_mul() from Generalised_floating_point_multiplication#Phix

```--
-- =================================
--
--
-- Uses b_add() and b_mul() from Generic_multiplication
with trace

--<next 210 lines copied from Generic_multiplication.exw>
constant decimal = "0123456789"

function negate(string b, alphabet)
--
-- negate b (can be balanced or unbalanced)
--
if alphabet[1]='0' then
-- eg "-123" <==> "123"
if b!="0" then
if b[1]='-' then
b = b[2..\$]
else
b = "-"&b
end if
end if
else
-- balanced: mirror [non-0] digits
-- eg "-0+" (ie -8) <==> "+0-" (ie +8)
for i=1 to length(b) do
if b[i]!='.' then
b[i] = alphabet[-find(b[i],alphabet)]
end if
end for
end if
return b
end function

function b_trim(string b)
-- (common code)
-- trim trailing ".000"
if find('.',b) then
b = trim_tail(trim_tail(b,'0'),'.')
end if
-- trim leading zeroes, but not "0.nnn" -> ".nnn"
-- [hence we cannot use the standard trim_head()]
while length(b)>1 and b[1]='0' and b[2]!='.' do
b = b[2..\$]
end while
if b="" then b="0" end if
return b
end function

forward function b_sub(string a, b, alphabet)

integer base = length(alphabet),
zdx = find('0',alphabet),
carry = 0, da, db, digit
if zdx=1 then
-- (let me know if you can fix this for me!)
--      if a[1]='-' or b[1]='-' then ?9/0 end if -- +ve only
if a[1]='-' then    -- (-a)+b == b-a
return b_sub(b,negate(a,alphabet),alphabet)
end if
if b[1]='-' then    -- a+(-b) == a-b
return b_sub(a,negate(b,alphabet),alphabet)
end if
end if
bdt = find('.',b)
-- remove the '.'s and zero-pad the shorter as needed
--   (thereafter treat them as two whole integers)
-- eg "1.23"+"4.5" -> "123"+"450" (leaving adt==2)
if bdt then bdt = length(b)-bdt+1;  b[-bdt..-bdt] = "" end if
end if
end if
if length(a)<length(b) then
{a,b} = {b,a}   -- ensure b is the shorter
end if
for i=-1 to -length(a) by -1 do
da = iff(i<-length(a)?0:find(a[i],alphabet)-zdx)
db = iff(i<-length(b)?0:find(b[i],alphabet)-zdx)
digit = da + db + carry + zdx
carry = iff(digit>base?+1:iff(digit<1?-1:0))
a[i] = alphabet[digit-carry*base]
if i<-length(b) and carry=0 then exit end if
end for
if carry then
a = alphabet[carry+zdx]&a
end if
end if
a = b_trim(a)
return a
end function

function a_smaller(string a, b, alphabet)
-- return true if a is smaller than b
-- if not balanced then both are +ve
if length(a)!=length(b) then ?9/0 end if -- sanity check
for i=1 to length(a) do
integer da = find(a[i],alphabet),
db = find(b[i],alphabet),
c = compare(a,b)
if c!=0 then return c<0 end if
end for
return false -- (=, which is not <)
end function

function b_sub(string a, b, alphabet)
integer base = length(alphabet),
zdx = find('0',alphabet),
carry = 0, da, db, digit
if zdx=1 then
if a[1]='-' then    -- (-a)-b == -(a+b)
end if
if b[1]='-' then    -- a-(-b) == a+b
end if
end if
bdt = find('.',b)
-- remove the '.'s and zero-pad the shorter as needed
--   (thereafter treat them as two whole integers)
-- eg "1.23"+"4.5" -> "123"+"450" (leaving adt==2)
if bdt then bdt = length(b)-bdt+1;  b[-bdt..-bdt] = "" end if
end if
end if
bool bNegate = false
if length(a)<length(b)
or (length(a)=length(b) and a_smaller(a,b,alphabet)) then
bNegate = true
{a,b} = {b,a}   -- ensure b is the shorter/smaller
end if
for i=-1 to -length(a) by -1 do
da = iff(i<-length(a)?0:find(a[i],alphabet)-zdx)
db = iff(i<-length(b)?0:find(b[i],alphabet)-zdx)
digit = da - (db + carry) + zdx
carry = digit<=0
a[i] = alphabet[digit+carry*base]
if i<-length(b) and carry=0 then exit end if
end for
if carry then
?9/0    -- should have set bNegate above...
end if
end if
a = b_trim(a)
if bNegate then
a = negate(a,alphabet)
end if
return a
end function

function b_mul(string a, b, alphabet)
integer base = length(alphabet),
zdx = find('0',alphabet),
dpa = find('.',a),
dpb = find('.',b),
ndp = 0
if dpa then ndp += length(a)-dpa; a[dpa..dpa] = "" end if
if dpb then ndp += length(b)-dpb; b[dpb..dpb] = "" end if
string pos = a, res = "0"
if zdx!=1 then
-- balanced number systems
string neg = negate(pos,alphabet)
for i=length(b) to 1 by -1 do
integer m = find(b[i],alphabet)-zdx
while m do
m += iff(m<0?+1:-1)
end while
pos &= '0'
neg &= '0'
end for
else
-- non-balanced (normal) number systems
bool negative = false
if a[1]='-' then a = a[2..\$]; negative = true end if
if b[1]='-' then b = b[2..\$]; negative = not negative end if
for i=length(b) to 1 by -1 do
integer m = find(b[i],alphabet)-zdx
while m>0 do
m -= 1
end while
pos &= '0'
end for
if negative then res = negate(res,alphabet) end if
end if
if ndp then
res[-ndp..-ndp-1] = "."
end if
res = b_trim(res)
return res
end function
--</copied from Generic_multiplication.exw>

function normalise_decimal(string a)
--
-- eg "12.34e-3" ==> "0.01234"
--     and "1e2" ==> "100"
--
integer d = find('.',a),
e = find('e',a)
if e then
integer {{z}} = scanf(a[e+1..\$],"%d")
a = a[1..e-1]
if d then
-- eg 12.34e-3 == 1234e-5
a[d..d] = ""
z -= length(a)-d+1
end if
if z>=0 then
-- eg 1e2 ==> 100
a &= repeat('0',z)
elsif z<-length(a) then
-- eg 1234e-5 ==> 0.01234
a = "0."&repeat('0',-z-length(a))&a
else
-- eg 1234e-3 ==> 1.234
a[z..z-1] = "."
end if
end if
return a
end function

function e_notation(string a)
-- eg "1000000" ==> "1e6"
if find('.',a) then ?9/0 end if -- (to do)
integer l = length(a)
a = trim_tail(a,".0")
l -= length(a)
if l!=0 then
a &=sprintf("e%d",l)
end if
return a
end function

string s = "12345679",
t = "123456790"
integer e = 63
for n = -7 to 21 do
string bd = normalise_decimal(sprintf("%se%d",{s,e})),
e1 = normalise_decimal(sprintf("1e%d",e)),
printf(1,"%2d res : %s\n",{n,e_notation(res)})
s = t & s
e -= 9
end for
```

same ouput

## Racket

Racket has native arbitrary precision numbers (if in doubt, prefixed with `#e...`)

The printed result is the exact difference of 1e72 and the result. So those `0`s you see are exactly nothing.

```#lang racket
(define (f n (printf printf))
(define exponent (* (- n) 9))
(define mantissa
(for/fold ((m 0))
(+ (* m 1000000000) 12345679)))

(let ((rv (+ (expt 10 exponent) (* mantissa (expt 10 exponent) 81))))
(printf "~ae~a * 81 + 1e~a - 1e72 = ~a~%"
(~.a mantissa
#:max-width 20
#:limit-marker (format "..[~a].." (add1 (order-of-magnitude mantissa))))
exponent
exponent
(- #e1e72 rv))
rv))

(module+ test
(require rackunit)
(check-equal? (f -7 void) (expt 10 72))
(check-equal? (f -6 void) (expt 10 72)))

(module+ main
(displayln "number in brackets is TOTAL number of digits")
(for ((i (in-range -7 (add1 21)))) (f i)))
```
Output:
```number in brackets is TOTAL number of digits
12345679e63 * 81 + 1e63 - 1e72 = 0
12345679012345679e54 * 81 + 1e54 - 1e72 = 0
123456790123..[26]..e45 * 81 + 1e45 - 1e72 = 0
123456790123..[35]..e36 * 81 + 1e36 - 1e72 = 0
123456790123..[44]..e27 * 81 + 1e27 - 1e72 = 0
123456790123..[53]..e18 * 81 + 1e18 - 1e72 = 0
123456790123..[62]..e9 * 81 + 1e9 - 1e72 = 0
123456790123..[71]..e0 * 81 + 1e0 - 1e72 = 0
123456790123..[80]..e-9 * 81 + 1e-9 - 1e72 = 0
123456790123..[89]..e-18 * 81 + 1e-18 - 1e72 = 0
123456790123..[98]..e-27 * 81 + 1e-27 - 1e72 = 0
12345679012..[107]..e-36 * 81 + 1e-36 - 1e72 = 0
12345679012..[116]..e-45 * 81 + 1e-45 - 1e72 = 0
12345679012..[125]..e-54 * 81 + 1e-54 - 1e72 = 0
12345679012..[134]..e-63 * 81 + 1e-63 - 1e72 = 0
12345679012..[143]..e-72 * 81 + 1e-72 - 1e72 = 0
12345679012..[152]..e-81 * 81 + 1e-81 - 1e72 = 0
12345679012..[161]..e-90 * 81 + 1e-90 - 1e72 = 0
12345679012..[170]..e-99 * 81 + 1e-99 - 1e72 = 0
12345679012..[179]..e-108 * 81 + 1e-108 - 1e72 = 0
12345679012..[188]..e-117 * 81 + 1e-117 - 1e72 = 0
12345679012..[197]..e-126 * 81 + 1e-126 - 1e72 = 0
12345679012..[206]..e-135 * 81 + 1e-135 - 1e72 = 0
12345679012..[215]..e-144 * 81 + 1e-144 - 1e72 = 0
12345679012..[224]..e-153 * 81 + 1e-153 - 1e72 = 0
12345679012..[233]..e-162 * 81 + 1e-162 - 1e72 = 0
12345679012..[242]..e-171 * 81 + 1e-171 - 1e72 = 0
12345679012..[251]..e-180 * 81 + 1e-180 - 1e72 = 0
12345679012..[260]..e-189 * 81 + 1e-189 - 1e72 = 0
```

## Raku

(formerly Perl 6) As long as all values are kept as rationals (type `Rat`) calculations are done full precision.

```my \$e = 63;
for -7..21 -> \$n {
my \$num = '12345679' ~ '012345679' x (\$n+7);
my \$sum = \$_ + (\$num * \$_) * 81 given \$e > -20 ?? 10**\$e !! Rat.new(1,10**abs \$e);
printf "\$n:%s ", 10**72 == \$sum ?? 'Y' !! 'N';
\$e -= 9;
}
```
Output:
```-7:Y -6:Y -5:Y -4:Y -3:Y -2:Y -1:Y 0:Y 1:Y 2:Y 3:Y 4:Y 5:Y 6:Y 7:Y 8:Y 9:Y 10:Y 11:Y 12:Y 13:Y 14:Y 15:Y 16:Y 17:Y 18:Y 19:Y 20:Y 21:Y
```

## REXX

### base ten only

```           ┌────────────────────────────────────────────────────────────────────┐
┌─┘  This REXX program uses an  uncompressed  (or zoned)  BCD  which   └─┐
│ consumes one byte for each represented digit.  A leading sign (+ or -) │
│ is optional.  An exponent is also allowed which is preceded by a  ^.   │
│ The value of the exponent may have a leading sign  (+ or -).           │
│ Each numeral (digit)  is stored as its own character (glyph),  as well │
│ as the signs and exponent indicator.  There is essentially no limit on │
│ the number of digits in the mantissa or the exponent, but the value of │
│ the exponent is limited to around 16 million.  The mantissa may also   │
│ have a decimal point (.).                                              │
│                                                                        │
│ Method:  a table of twenty-eight BCD numbers is built, and a test case │
│ of adding that BCD number 81 times  (essentially multiplying by 81),   │
│ and then a number is added to that sum,  and the resultant sum should  │
│ result in the final sum of  1e72   (for all cases).                    │
│                                                                        │
└─┐  The number of digits for the precision is automatically adjusted. ┌─┘
└────────────────────────────────────────────────────────────────────┘
```
```/*REXX program performs  generalized floating point addition  using  BCD  numbers.      */
maxW= linesize() - 1                             /*maximum width allowed for displays.  */
/*Not all REXXes have the LINESIZE BIF.*/
_123= 012345679;   reps= 0;   mult= 63           /*vars used to construct test cases.   */
say left('── ────── ─', maxW, '─')                                  /*   "    header sep*/

do j=-7  to 21                                /*traipse through the test cases.      */
reps= reps + 1                                /*increase number of repetitions.      */
BCD.j= strip(copies(_123, reps)'^'mult,'L',0) /*construct a zoned BCD.               */
if j//3==0  then BCD.J= '+'BCD.j              /*add a leading plus sign every 3rd #. */
parse var BCD.j '^' pow                       /*get the exponent part of the number. */
_=right(j, 2)  right(addend.j, 6)             /*construct the prefix for a line.     */
aLine= _  BCD.j                               /*construct a line for the output.     */
if length(aLine)<maxW  then say aLine         /*Does it fit on a line?  Display it.  */
else say _ ' ['length(BCD.j)  "digits]"         /*otherwise...*/
mult= mult - 9                                /*decrease the multiplier's exponent.  */
maxDigs= length(BCD.j) + abs(pow) + 5         /*compute the maximum precision needed.*/
if maxDigs>digits()  then numeric digits maxDigs         /*increase digits if needed.*/
end    /*j*/

say copies('═', maxW)                            /*display a fence for separation.      */
times= 81                                        /*the number of times to   add   it.   */

do k=-7  to 21                                /*traipse through the test cases.      */
parse var BCD.k   mantissa  '^'  exponent     /*decompose the zoned  BCD  number.    */
x= mantissa'e'exponent                        /*reconstitute the original number.    */
sum= 0                                        /*prepare for the 81 additions.        */
do times
sum= sum + x                      /*multiplying the hard way, yuppers!   */
end

sum= (sum + addend.k) / 1                     /*one method to elide trailing zeroes. */
_= format(sum, , , , 0)                       /*force sum ──► exponential format.    */
say right(k,3) 'sum=' translate(_, "e", 'E')  /*use a lowercase  "E"  for exponents. */
end   /*k*/
/*stick a fork in it,  we're all done. */
```

This REXX program makes use of   LINESIZE   REXX program (or BIF) which is used to determine the screen width (or linesize) of the terminal (console).
The   LINESIZE.REX   REXX program is included here   ───►   LINESIZE.REX.

output :

'

``` # addend               uncompressed (zoned) BCD number
── ────── ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
-7   1e63 12345679^63
-6   1e54 +12345679012345679^54
-5   1e45 12345679012345679012345679^45
-4   1e36 12345679012345679012345679012345679^36
-3   1e27 +12345679012345679012345679012345679012345679^27
-2   1e18 12345679012345679012345679012345679012345679012345679^18
-1    1e9 12345679012345679012345679012345679012345679012345679012345679^9
0    1e0 +12345679012345679012345679012345679012345679012345679012345679012345679^0
1   1e-9 12345679012345679012345679012345679012345679012345679012345679012345679012345679^-9
2  1e-18 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-18
3  1e-27 +12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-27
4  1e-36 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-36
5  1e-45 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-45
6  1e-54 +12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-54
7  1e-63 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-63
8  1e-72 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-72
9  1e-81 +12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-81
10  1e-90 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-90
11  1e-99 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-99
12 1e-108 +12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-108
13 1e-117  [193 digits]
14 1e-126  [202 digits]
15 1e-135  [212 digits]
16 1e-144  [220 digits]
17 1e-153  [229 digits]
18 1e-162  [239 digits]
19 1e-171  [247 digits]
20 1e-180  [256 digits]
21 1e-189  [266 digits]
═══════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════
-7 sum=1e+72
-6 sum=1e+72
-5 sum=1e+72
-4 sum=1e+72
-3 sum=1e+72
-2 sum=1e+72
-1 sum=1e+72
0 sum=1e+72
1 sum=1e+72
2 sum=1e+72
3 sum=1e+72
4 sum=1e+72
5 sum=1e+72
6 sum=1e+72
7 sum=1e+72
8 sum=1e+72
9 sum=1e+72
10 sum=1e+72
11 sum=1e+72
12 sum=1e+72
13 sum=1e+72
14 sum=1e+72
15 sum=1e+72
16 sum=1e+72
17 sum=1e+72
18 sum=1e+72
19 sum=1e+72
20 sum=1e+72
21 sum=1e+72
```

### any base

```/*REXX program performs  generalized floating point addition  using  BCD  numbers.      */
parse arg base .                                 /*obtain optional argument from the CL.*/
if base=='' | base==","  then base= 10           /*Not specified?  Then use the default.*/
maxW= linesize() - 1                             /*maximum width allowed for displays.  */
/*Not all REXXes have the LINESIZE BIF.*/
_123= 012345679;   reps= 0;   mult= 63           /*vars used to construct test cases.   */
say left('── ────── ─', maxW, '─')                                  /*   "    header sep*/

do j=-7  to 21                                /*traipse through the test cases.      */
reps= reps + 1                                /*increase number of repetitions.      */
BCD.j= strip(copies(_123, reps)'^'mult,'L',0) /*construct a zoned BCD.               */
if j//3==0  then BCD.J= '+'BCD.j              /*add a leading plus sign every 3rd #. */
parse var BCD.j '^' pow                       /*get the exponent part of the number. */
_= right(j, 2)  right(addend.j, 6)            /*construct the prefix for a line.     */
aLine= _  BCD.j                               /*construct a line for the output.     */
if length(aLine)<maxW  then say aLine         /*Does it fit on a line?  Display it.  */
else say _ ' ['length(BCD.j)  "digits]"         /*otherwise...*/
mult= mult - 9                                /*decrease the multiplier's exponent.  */
maxDigs= length(BCD.j) + abs(pow) + 5         /*compute the maximum precision needed.*/
if maxDigs>digits()  then numeric digits maxDigs         /*increase digits if needed.*/
end    /*j*/

say copies('═', maxW)                            /*display a fence for separation.      */
times= 81                                        /*the number of times to   add   it.   */

do k=-7  to 21                                /*traipse through the test cases.      */
parse var BCD.k   mantissa  '^'  exponent     /*decompose the zoned  BCD  number.    */
x= mantissa'e'exponent                        /*reconstitute the original number.    */
sum= 0                                        /*prepare for the 81 additions.        */
do times
sum= sum + x                      /*multiplying the hard way, yuppers!   */
end

sum= (sum + addend.k) / 1                     /*one method to elide trailing zeroes. */
_= format(sum, , , , 0)                       /*force sum ──► exponential format.    */
_bX= base(_ / 1,  base)                       /*this expresses    _   in base  BASE. */
say right(k,3) 'sum=' translate(_bX, "e", 'E')  /*use a lowercase "E" for exponents. */
end   /*k*/                                   /*output is in base   BASEX.           */

exit 0                                           /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
base: procedure;  parse arg x 1 s 2 1 ox,tt,ii,left_,right_;   f= 'BASE'
@#= 0123456789;  @abc='abcdefghijklmnopqrstuvwxyz';      @abcu= @abc;   upper @abcu
\$= \$basex()                                /*character string of maximum base.    */
m= length(\$) - 1                           /*M:  the maximum base that can be used*/
c= left_\=='' | right_\==''
if tt==''  then tt= 10                     /*assume base  ten  if omitted.        */
if ii==''  then ii= 10                     /*assume base  ten  if omitted.        */
i= abs(ii)
t= abs(tt)
if t==999 | t=="*"  then t= m
if t>m & \c  then call er81 t,2 m f'-to'
if i>m       then call er81 i,2 m f'-from'

if \c  then do                             /*build character string for base ?    */
!= substr(\$, 1 + 10*(tt<0), t) /*the character string for base  T.    */
if tt<0  then != 0  ||  !      /*prefix a zero  if  negative base.    */
end

if x==''  then if c  then return left_ || t || right_
else return left(!, t)

@= substr(\$, 1 + 10*(ii<0), i)              /*@:  legal characters for base  X.   */
oS=                                         /*the original sign placeholder.      */
if s='-' | s="+"  then do                   /*process the sign (if any).          */
x= substr(x,2)       /*strip the sign character.           */
oS= s                /*save the original sign glyph.       */
end

if (ii>10 & ii<37) | (ii<0 & ii>-27)  then upper x     /*should we uppercase it ? */

/*Base 10?   Then it must be a number.*/

if pos('-', x)\==0 |,                       /*too many minus signs ?              */
pos('+', x)\==0 |,                       /*too many  plus signs ?              */
x==.            |,                       /*is it a single decimal point ?      */
x==''               then call er53 ox    /* ...  or a single  +  or  -  sign ? */

parse var x   w  '.'  g                     /*sep whole number from the fraction. */
if pos(., g)\==0  then call er53 ox         /*too many decimals points?           */
items.1= 0                                  /*number of whole part "digits".      */
items.2= 0                                  /*number of fractional "digitsd".     */

if c  then do                               /*any "digit" specifiers ?            */
do while w\==''              /*process the  "whole"  part.         */
parse var w    w.1  (left_)  w.2  (right_)  w
do j=1  for 2;  if w.j\==''  then call putit w.j,1
end   /*j*/
end     /*while*/

do while g\==''              /*process the fractional part.        */
parse var g g.1 (left_) g.2 (right_) g
do j=1  for 2;        if g.j\==''  then call putit g.j,2
end   /*j*/
end     /*while*/

_= 0;       p= 0                 /*convert the whole number part.      */

do j=items.1 to 1 by -1;  _= _ + item.1.j * (i**p)
p= p + 1                          /*increase the power of the base.  */
end   /*j*/

w=_;        p= 0;      _= 0      /*convert the fractional part.        */

do j=1 to items.2;        _=_+item.2.j/i**p
p= p + 1                       /*increase power of the base.         */
end   /*j*/

g= strip( strip(_, 'L', 0), , .) /*strip leading decimal point.        */
if g=0  then g=                  /*no signifcant fract. part.*/
end

__= w || g                                  /*verify re-composed number.*/
_= verify(__,@'.')                          /*# have any unusual digits?*/
if _\==0  then call er48,ox,substr(__, _, 1)    '[for'    f    i"]"    /*oops─say.*/

if i\==10  then do                           /*convert number base I ──► base 10. */
/*...  but only if not base 10.      */
_= 0;  p= 0                  /*convert the whole number part.     */

do j=length(w)  to 1  by -1   while w\==''
_= _ + ((pos( substr(w, j, 1),  @) - 1)  * i **p)
p= p + 1    /*increase the power of the base.    */
end   /*j*/
w= _;  _= 0;   p= 1          /*convert the fractional part.       */

do j=1  for length(g)
_= _ d + ( (pos( substr(g, j, 1), @) - 1)   /  i**p)
p= p + 1                  /*increase the power of the base.    */
end   /*j*/
g= _
end
else if g\=='' then g="."g        /*reinsert the period if needed.     */

if t\==10  then do                           /*convert base10 number to base  T.  */
if w\=='' then do            /*convert the whole number part.     */
do j=1;   _= t**j;      if _>w  then leave
end   /*J*/
n=
do k=j-1  to 1  by -1;    _= t**k;      d= w % _
if c  then n= n      left_ || d || right_
else n= n  ||  substr(!,  1 + d,  1)
w= w // _
end   /*k*/
if c  then w= n      left_  ||  w  ||  right_
else w= n  ||  substr(!, 1 + w,  1)
end

if g\=='' then do;  n=       /*convert the fractional part.       */
do digits()+1;   if g==0 then leave
p= g * t;        g = p // 1;   d= trunc(p)
if c  then n= n      left_ || d || right_
else n= n  ||  substr(!,  d + 1,  1)
end   /*digits···*/
if n==0    then n=
if n\==''  then n= '.'n   /*is it only a fraction?*/
g= n
end
end

return oS || p( strip( space(w), 'L', 0)strip( strip(g, , 0),  "T",.)   0)
/*──────────────────────────────────────────────────────────────────────────────────────*/
\$basex: return @# || @abcu || @abc || space( translate(,
xrange('1'x, "fe"x), , @#'.+-'@abc || @abcu"0708090a0b0c0d"x),  0)
/*──────────────────────────────────────────────────────────────────────────────────────*/
num:    procedure;   parse arg x .,f,q;  if x=='' then return x
if isnum(x)  then return x/1;    x= space( translate(x, , ','), 0)
if isnum(x)  then return x/1;    return numnot()
/*──────────────────────────────────────────────────────────────────────────────────────*/
putit:  parse arg px,which;  if \isint(px)  then px= numx(px)
items.which= items.which + 1;       _= items.which;    item.which._= px;    return
/*──────────────────────────────────────────────────────────────────────────────────────*/
er:     say '***error!***'; say; say arg(1); say; exit 13
er48:   call er arg(1) 'contains invalid characters:'  arg(2)
er53:   call er arg(1) 'not numeric'
er81:   call er arg(1) 'must be in the range:'         arg(2)
isint:  return datatype( arg(1), 'W')
isnum:  return datatype( arg(1), 'N')
numnot: if q==1  then return x;                        call er53 x
numx:   return num( arg(1), arg(2), 1)
p:      return subword( arg(1), 1, max(1, words( arg(1) ) - 1) )
```
output   when using the (base) input of:     62
``` # addend               uncompressed (zoned) BCD number
── ────── ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
-7   1e63 12345679^63
-6   1e54 +12345679012345679^54
-5   1e45 12345679012345679012345679^45
-4   1e36 12345679012345679012345679012345679^36
-3   1e27 +12345679012345679012345679012345679012345679^27
-2   1e18 12345679012345679012345679012345679012345679012345679^18
-1    1e9 12345679012345679012345679012345679012345679012345679012345679^9
0    1e0 +12345679012345679012345679012345679012345679012345679012345679012345679^0
1   1e-9 12345679012345679012345679012345679012345679012345679012345679012345679012345679^-9
2  1e-18 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-18
3  1e-27 +12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-27
4  1e-36 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-36
5  1e-45 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-45
6  1e-54 +12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-54
7  1e-63 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-63
8  1e-72 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-72
9  1e-81 +12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-81
10  1e-90 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-90
11  1e-99 12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-99
12 1e-108 +12345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679012345679^-108
13 1e-117  [193 digits]
14 1e-126  [202 digits]
15 1e-135  [212 digits]
16 1e-144  [220 digits]
17 1e-153  [229 digits]
18 1e-162  [239 digits]
19 1e-171  [247 digits]
20 1e-180  [256 digits]
21 1e-189  [266 digits]
═══════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════
-7 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
-6 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
-5 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
-4 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
-3 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
-2 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
-1 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
0 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
1 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
2 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
3 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
4 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
5 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
6 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
7 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
8 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
9 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
10 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
11 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
12 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
13 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
14 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
15 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
16 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
17 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
18 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
19 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
20 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
21 sum= 20wgMRBdL7rq2Kntz9B7xkSrr7S8ALuO5sk25dQY4
```

## Ruby

No code, it's built in (uses '*' for multiplication):

```p 12345679e63 * 81 + 1e63
p 12345679012345679e54 * 81 + 1e54
p 12345679012345679012345679e45 * 81 + 1e45
p 12345679012345679012345679012345679e36 * 81 + 1e36
```

All result in 1.0e+72.

## Tcl

Tcl does not allow overriding the default mathematical operators (it does allow you to define your own expression engine — this is even relatively simple to do — but this is out of the scope of this task) but it also allows expressions to be written using a Lisp-like prefix form:

```namespace path ::tcl::mathop
for {set n -7; set e 63} {\$n <= 21} {incr n;incr e -9} {
append m 012345679
puts \$n:[+ [* [format "%se%s" \$m \$e] 81] 1e\${e}]
}
```

The above won't work as intended though; the default implementation of the mathematical operators does not handle arbitrary precision floats (though in fact it will produce the right output with these specific values; this is a feature of the rounding used, and the fact that the exponent remains expressible in an IEEE double-precision float). So here is a version that does everything properly:

```namespace eval longfloat {
proc + {num args} {
set num [impl::Tidy \$num]
foreach x \$args {
set num [impl::Add \$num [impl::Tidy \$x]]
}
return [impl::Normalize \$num]
}
proc * {num args} {
set num [impl::Tidy \$num]
foreach x \$args {
set num [impl::Mul \$num [impl::Tidy \$x]]
}
return [impl::Normalize \$num]
}

namespace export + *

# This namespace contains the implementations of the operations and
# isn't intended to be called directly by the rest of the program.
namespace eval impl {
variable FloatRE \
{(?i)^([-+]?(?:[0-9]+(?:\.[0-9]*)?|\.[0-9]+))(?:e([-+]?[0-9]+))?\$}

proc Tidy {n} {
variable FloatRE
# Parse the input
if {[llength \$n] == 2} {
return \$n
} elseif {[llength \$n] != 1} {
return -level 2 -code error "non-numeric argument"
} elseif {![regexp \$FloatRE \$n -> mantissa exponent]} {
return -level 2 -code error "non-numeric argument"
}

# Default exponent is zero
if {\$exponent eq ""} {
set exponent 0
}
# Eliminate the decimal point
set bits [split \$mantissa .]
if {[llength \$bits] == 2} {
incr exponent [expr {-[string length [lindex \$bits 1]]}]
set mantissa [join \$bits ""]
}
return [list [regsub {^([-+]?)0*([0-9])} \$mantissa {\1\2}] \$exponent]
}

proc Normalize {n} {
lassign \$n mantissa exponent
# Trim useless trailing zeroes
while {[regexp {^([-+]?.+?)(0+)\$} \$mantissa -> head tail]} {
incr exponent [string length \$tail]
}
return \${mantissa}e\${exponent}
}

# Addition and multiplication on pairs of arbitrary-precision floats,
# in decomposed form
lassign \$a am ae
lassign \$b bm be
set de [expr {\$ae - \$be}]
if {\$de < 0} {
append bm [string repeat 0 [expr {-\$de}]]
} elseif {\$de > 0} {
incr ae [expr {-\$de}]
append am [string repeat 0 \$de]
}
list [expr {\$am+\$bm}] \$ae
}
proc Mul {a b} {
lassign \$a am ae
lassign \$b bm be
list [expr {\$am * \$bm}] [expr {\$ae + \$be}]
}
}
}
```

Now we can demonstrate (compare with the original code to see how little has changed syntactically):

```namespace path longfloat
for {set n -7; set e 63} {\$n <= 21} {incr n;incr e -9} {
append m 012345679
puts \$n:[+ [* [format "%se%s" \$m \$e] 81] 1e\${e}]
}
```
Output (trimmed):
```-7:1e72
-6:1e72
-5:1e72
-4:1e72
………
18:1e72
19:1e72
20:1e72
21:1e72
```

If we extend the series to 40, we still get correct computations, and that's something which is not computable with normal IEEE arithmetic (due to problems with limits on the size of exponent) even at reduced precision.

Obviously, changing the code inside the `impl` namespace would alter how the calculation was carried out.

## Wren

Translation of: Kotlin
Library: wren-fmt
Library: wren-big

The BigRat class in the above module allows not only rational numbers but decimal numbers of any size to be represented exactly. However, no bases other than 10 are supported.

Although the BigRat type supports multiplication, repeated addition has been used as in the Kotlin example.

```import "./big" for BigRat
import "./fmt" for Fmt

var repeatedAdd = Fn.new { |br, times|
var sum = BigRat.zero
for (i in 0...times) sum = sum + br
return sum
}

var s = "12345679"
var t = "123456790"
var e = 63
var ans = BigRat.fromDecimal("1e72")
for (n in -7..21) {
var br = BigRat.fromDecimal("%(s)e%(e)")
var oneE = BigRat.fromDecimal("1e%(e)")
var res = repeatedAdd.call(temp, 9) + oneE
Fmt.print("\$2d : 1e72? \$s", n, res == ans)
s = t + s
e = e - 9
}
```
Output:
```-7 : 1e72? true
-6 : 1e72? true
-5 : 1e72? true
-4 : 1e72? true
-3 : 1e72? true
-2 : 1e72? true
-1 : 1e72? true
0 : 1e72? true
1 : 1e72? true
2 : 1e72? true
3 : 1e72? true
4 : 1e72? true
5 : 1e72? true
6 : 1e72? true
7 : 1e72? true
8 : 1e72? true
9 : 1e72? true
10 : 1e72? true
11 : 1e72? true
12 : 1e72? true
13 : 1e72? true
14 : 1e72? true
15 : 1e72? true
16 : 1e72? true
17 : 1e72? true
18 : 1e72? true
19 : 1e72? true
20 : 1e72? true
21 : 1e72? true
```