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Avoid signed integer overflow in scm_product

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* libguile/numbers.c (scm_product): Avoid signed integer overflow, which
  modern C compilers are allowed to assume will never happen, thus
  allowing them to optimize out our overflow checks.

* test-suite/tests/numbers.test (*): Add tests.
This commit is contained in:
Mark H Weaver 2012-12-07 11:53:00 -05:00
parent e6a730b22a
commit 2355f01709
2 changed files with 20 additions and 4 deletions
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14
libguile/numbers.c
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@ -7640,10 +7640,16 @@ scm_product (SCM x, SCM y)
if (SCM_LIKELY (SCM_I_INUMP (y)))
{
scm_t_inum yy = SCM_I_INUM (y);
scm_t_inum kk = xx * yy;
SCM k = SCM_I_MAKINUM (kk);
if ((kk == SCM_I_INUM (k)) && (kk / xx == yy))
return k;
#if SCM_I_FIXNUM_BIT < 32 && SCM_HAVE_T_INT64
scm_t_int64 kk = xx * (scm_t_int64) yy;
if (SCM_FIXABLE (kk))
return SCM_I_MAKINUM (kk);
#else
scm_t_inum axx = (xx > 0) ? xx : -xx;
scm_t_inum ayy = (yy > 0) ? yy : -yy;
if (SCM_MOST_POSITIVE_FIXNUM / axx >= ayy)
return SCM_I_MAKINUM (xx * yy);
#endif
else
{
SCM result = scm_i_inum2big (xx);