ISBN13 check digit: Difference between revisions

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@@ Line 1,170: / Line 1,170: @@
 =={{header|Forth}}==
+The following word not only identifies correct 13 digit ISBN (and EAN) codes, but also 8 digit EAN and GTIN codes.
 <lang>: is-digit [char] 0 - 10 u< ;
 : isbn?                                ( a n -- f)
-- 2dup chars + c@ [char] 0 - >r 2>r 0 1 2r> bounds ?do
+- chars over + 2>r 0 1 2r> ?do
-    dup i c@ dup is-digit
-    if [char] 0 - * rot + swap 3 * 8 mod else drop drop then
-  loop drop r> + 10 mod 0=
-;</lang>
-The following slightly modified word not only identifies correct 13 digit ISBN (and EAN) codes, but also 8 digit EAN and GTIN codes:
-<lang>: isbn?                                ( a n -- f)
-  bounds 2>r 0 dup 2r@ ?do i c@ is-digit + loop abs 1- 1 and 2* 1+ 2r> ?do
     dup i c@ dup is-digit              \ get length and factor, setup loop
     if [char] 0 - * rot + swap 3 * 8 mod else drop drop then
-  loop drop 10 mod 0=                  \ now calculate checksum
+  -1 chars +loop drop 10 mod 0=        \ now calculate checksum
 ;</lang>
 {{out}}