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Someone reported a bug a while ago in the bignum support: a factorial
procedure wasn't giving the right answer. e.g.,:
(define (factiter x tot)
(if (= x 1)
tot
(factiter (- x 1) (* x tot))))
(define (fact x) (factiter x 1))
(define bad (fact 7350))
(define str (number->string bad))
(define len (string-length str))
(define last (substring str (- len 40) len))
(display last)
should print a string of zeros. sometimes it works, but you still get
the wrong answer if you type "bad" a few times.
it's probably system-specific: i get the bug on i586/linux;
gcc 2.7.2 and gcc 2.8.1, but only if numbers.c is optimised:
-O will do.
the problem seems to be in the bignum -> string conversion.
this is a work-around: i don't know why it helps.
--- numbers.c.orig Wed Oct 7 22:31:18 1998
+++ numbers.c Wed Oct 7 22:28:56 1998
@@ -1387,7 +1387,8 @@
SCM b;
register unsigned int radix;
{
- SCM t = scm_copybig(b, 0); /* sign of temp doesn't matter */
+ /* volatile to avoid the (fact 7350) bug. */
+ volatile SCM t = scm_copybig(b, 0); /* sign of temp doesn't matter */
register SCM_BIGDIG *ds = SCM_BDIGITS(t);
scm_sizet i = SCM_NUMDIGS(t);
scm_sizet j = radix==16 ? (SCM_BITSPERDIG*i)/4+2