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Optimize scm_i_divide2double for integers less than 2^DBL_MANT_DIG.

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* libguile/numbers.c (scm_i_divide2double): Optimize for common case
  when both operands are less than 2^DBL_MANT_DIG (normally 2^53).
This commit is contained in:
Mark H Weaver 2013-03-19 22:38:45 -04:00
parent 1d64b4edb9
commit c8248c8ed5
1 changed files with 11 additions and 1 deletions
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12
libguile/numbers.c
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@ -475,8 +475,17 @@ scm_i_divide2double (SCM n, SCM d)
mpz_t nn, dd, lo, hi, x; mpz_t nn, dd, lo, hi, x;
ssize_t e; ssize_t e;
if (SCM_I_INUMP (d)) if (SCM_LIKELY (SCM_I_INUMP (d)))
{ {
if (SCM_LIKELY (SCM_I_INUMP (n)
&& (SCM_I_FIXNUM_BIT-1 <= DBL_MANT_DIG
|| (SCM_I_INUM (n) < (1L << DBL_MANT_DIG)
&& SCM_I_INUM (d) < (1L << DBL_MANT_DIG)))))
/* If both N and D can be losslessly converted to doubles, then
we can rely on IEEE floating point to do proper rounding much
faster than we can. */
return ((double) SCM_I_INUM (n)) / ((double) SCM_I_INUM (d));
if (SCM_UNLIKELY (scm_is_eq (d, SCM_INUM0))) if (SCM_UNLIKELY (scm_is_eq (d, SCM_INUM0)))
{ {
if (scm_is_true (scm_positive_p (n))) if (scm_is_true (scm_positive_p (n)))
@ -486,6 +495,7 @@ scm_i_divide2double (SCM n, SCM d)
else else
return 0.0 / 0.0; return 0.0 / 0.0;
} }
mpz_init_set_si (dd, SCM_I_INUM (d)); mpz_init_set_si (dd, SCM_I_INUM (d));
} }
else else