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log: add a separate path for ratios

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While not necessarily a bug, it is convenient to not overflow on very small
ratios. When feasible instead of converting to float, we compute log of the
number and the denominator and then return their difference.

c.f https://mailman.common-lisp.net/pipermail/ecl-devel/2022-July/011628.html
This commit is contained in:
Daniel Kochmański 2022-11-10 21:08:54 +01:00
parent 4d7ee7a301
commit b45dec9c32
2 changed files with 19 additions and 1 deletions
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19
src/c/numbers/log.d
View file

@ -17,6 +17,7 @@
#include <ecl/ecl.h>
#include <ecl/internal.h>
#include <complex.h>
#include <float.h>
#include <ecl/impl/math_dispatch.h>
#pragma STDC FENV_ACCESS ON
@ -88,6 +89,22 @@ ecl_log1_simple(cl_object x)
return ecl_make_single_float(logf(ecl_to_float(x)));
}
static cl_object
ecl_log1_ratio(cl_object x)
{
cl_object num = x->ratio.num;
cl_object den = x->ratio.den;
cl_index lnum = ecl_integer_length(num);
cl_index lden = ecl_integer_length(den);
if ((lnum > lden) ? (lnum - lden >= FLT_MAX_EXP) : (lden - lnum >= -FLT_MIN_EXP)) {
cl_object numlog = ecl_log1(num);
cl_object denlog = ecl_log1(den);
return ecl_minus(numlog, denlog);
} else {
return ecl_log1_simple(x);
}
}
static cl_object
ecl_log1_single_float(cl_object x)
{
@ -182,7 +199,7 @@ ecl_log1_clfloat(cl_object x)
#endif
MATH_DEF_DISPATCH1(log1, @[log], @[number],
ecl_log1_simple, ecl_log1_bignum, ecl_log1_simple,
ecl_log1_simple, ecl_log1_bignum, ecl_log1_ratio,
ecl_log1_single_float, ecl_log1_double_float, ecl_log1_long_float,
ecl_log1_complex,
ecl_log1_csfloat, ecl_log1_cdfloat, ecl_log1_clfloat);

1
src/h/impl/math_dispatch.h
View file

@ -54,6 +54,7 @@ typedef cl_object (*math_one_arg_fn)(cl_object);
} \
return name##dispatch[t](arg); \
}
#define MATH_DEF_DISPATCH1(name,id,type,fix,big,ratio, \
single_float,double_float,long_float, \
complex,csfloat,cdfloat,clfloat) \