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(scm_inexact_to_exact): Don't depend on what double->long

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cast gives for values bigger than a long, or for nan or inf.
This commit is contained in:
Kevin Ryde 2003-10-09 00:38:51 +00:00
parent f09fe63732
commit 2be24db4d7
1 changed files with 19 additions and 7 deletions
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26
libguile/numbers.c
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@ -4337,14 +4337,26 @@ SCM_DEFINE (scm_inexact_to_exact, "inexact->exact", 1, 0, 0,
return z;
else if (SCM_REALP (z))
{
double u = floor (SCM_REAL_VALUE (z) + 0.5);
long lu = (long) u;
if (SCM_FIXABLE (lu))
return SCM_MAKINUM (lu);
else if (!xisinf (u) && !xisnan (u))
return scm_i_dbl2big (u);
else
/* SCM_MOST_POSITIVE_FIXNUM+1 and SCM_MOST_NEGATIVE_FIXNUM are both
powers of 2, so there's no rounding when making "double" values
from them. If plain SCM_MOST_POSITIVE_FIXNUM was used it could get
rounded on a 64-bit machine, hence the "+1".
The use of floor() to force to an integer value ensures we get a
"numerically closest" value without depending on how a double->long
cast or how mpz_set_d will round. For reference, double->long
probably follows the hardware rounding mode, mpz_set_d truncates
towards zero. */
double u = SCM_REAL_VALUE (z);
if (xisinf (u) || xisnan (u))
scm_num_overflow (s_scm_inexact_to_exact);
u = floor (u + 0.5);
if (u < (double) (SCM_MOST_POSITIVE_FIXNUM+1)
&& u >= (double) SCM_MOST_NEGATIVE_FIXNUM)
return SCM_MAKINUM ((long) u);
else
return scm_i_dbl2big (u);
}
else
SCM_WRONG_TYPE_ARG (1, z);