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Optimize logarithms using scm_i_big2dbl_2exp

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* libguile/numbers.c (log_of_exact_integer_with_size): Removed.

  (log_of_exact_integer): Handle bignums too large to fit in a double
  using 'scm_i_big2dbl_2exp' instead of 'scm_integer_length' and
  'scm_ash'.

  (log_of_fraction): Use 'log_of_exact_integer' instead of
  'log_of_exact_integer_with_size'.
This commit is contained in:
Mark H Weaver 2013-03-03 05:02:53 -05:00
parent 1eb6a33a30
commit 7f34acd8a4
1 changed files with 12 additions and 18 deletions
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30
libguile/numbers.c
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@ -9600,26 +9600,20 @@ log_of_shifted_double (double x, long shift)
return scm_c_make_rectangular (ans, M_PI);
}
/* Returns log(n), for exact integer n of integer-length size */
static SCM
log_of_exact_integer_with_size (SCM n, long size)
{
long shift = size - 2 * scm_dblprec[0];
if (shift > 0)
return log_of_shifted_double
(scm_to_double (scm_ash (n, scm_from_long(-shift))),
shift);
else
return log_of_shifted_double (scm_to_double (n), 0);
}
/* Returns log(n), for exact integer n */
static SCM
log_of_exact_integer (SCM n)
{
return log_of_exact_integer_with_size
(n, scm_to_long (scm_integer_length (n)));
if (SCM_I_INUMP (n))
return log_of_shifted_double (SCM_I_INUM (n), 0);
else if (SCM_BIGP (n))
{
long expon;
double signif = scm_i_big2dbl_2exp (n, &expon);
return log_of_shifted_double (signif, expon);
}
else
scm_wrong_type_arg ("log_of_exact_integer", SCM_ARG1, n);
}
/* Returns log(n/d), for exact non-zero integers n and d */
@ -9630,8 +9624,8 @@ log_of_fraction (SCM n, SCM d)
long d_size = scm_to_long (scm_integer_length (d));
if (abs (n_size - d_size) > 1)
return (scm_difference (log_of_exact_integer_with_size (n, n_size),
log_of_exact_integer_with_size (d, d_size)));
return (scm_difference (log_of_exact_integer (n),
log_of_exact_integer (d)));
else if (scm_is_false (scm_negative_p (n)))
return scm_from_double
(log1p (scm_to_double (scm_divide2real (scm_difference (n, d), d))));