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Fix exp2l inaccuracy (bug 13824).

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This commit is contained in:
Joseph Myers 2012-03-22 12:55:19 +00:00
parent c0df8e693f
commit 48e44791e4
4 changed files with 69 additions and 9 deletions
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7
ChangeLog
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@ -1,5 +1,12 @@
2012-03-22 Joseph Myers <joseph@codesourcery.com>
[BZ #13824]
* math/e_exp2l.c: Include <float.h>.
(__ieee754_exp2l): Handle overflow and underflow cases
separately. Only pass fractional part of argument to
__ieee754_expl.
* math/libm-test.inc (exp2_test): Add more tests.
* sysdeps/ieee754/ldbl-128/k_cosl.c (__kernel_cosl): Negate y if
negating x to take absolute value.
* sysdeps/ieee754/ldbl-128/k_sincosl.c (__kernel_sincosl):

12
NEWS
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@ -11,12 +11,12 @@ Version 2.16
174, 350, 411, 2541, 2547, 2548, 2551, 2552, 2553, 2554, 2562, 2563, 2565,
2566, 2576, 3335, 3976, 3992, 4026, 4108, 4596, 4822, 5077, 5461, 5805,
5993, 6471, 6730, 6884, 6907, 6911, 9739, 9902, 10110, 10135, 10140, 10210,
10545, 10716, 11174, 11322, 11365, 11451, 11494, 12047, 13058, 13525,
13526, 13527, 13528, 13529, 13530, 13531, 13532, 13533, 13547, 13551,
13552, 13553, 13555, 13559, 13566, 13583, 13618, 13637, 13656, 13658,
13673, 13695, 13704, 13706, 13726, 13738, 13786, 13792, 13806, 13840,
13841, 13844, 13846, 13851, 13852, 13854, 13871, 13883
5993, 6471, 6730, 6884, 6907, 6911, 9739, 9902, 10110, 10135, 10140,
10210, 10545, 10716, 11174, 11322, 11365, 11451, 11494, 12047, 13058,
13525, 13526, 13527, 13528, 13529, 13530, 13531, 13532, 13533, 13547,
13551, 13552, 13553, 13555, 13559, 13566, 13583, 13618, 13637, 13656,
13658, 13673, 13695, 13704, 13706, 13726, 13738, 13786, 13792, 13806,
13824, 13840, 13841, 13844, 13846, 13851, 13852, 13854, 13871, 13883
* ISO C11 support:

44
math/e_exp2l.c
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@ -1,11 +1,49 @@
/* Compute 2^x.
Copyright (C) 2012 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <math.h>
#include <math_private.h>
#include <float.h>
long double
__ieee754_exp2l (long double x)
{
/* This is a very stupid and inprecise implementation. It'll get
replaced sometime (soon?). */
return __ieee754_expl (M_LN2l * x);
if (__builtin_expect (isless (x, (long double) LDBL_MAX_EXP), 1))
{
if (__builtin_expect (isgreaterequal (x, (long double) (LDBL_MIN_EXP
- LDBL_MANT_DIG
- 1)), 1))
{
int intx = (int) x;
long double fractx = x - intx;
return __scalbnl (__ieee754_expl (M_LN2l * fractx), intx);
}
else
{
/* Underflow or exact zero. */
if (__isinfl (x))
return 0;
else
return LDBL_MIN * LDBL_MIN;
}
}
else
/* Infinity, NaN or overflow. */
return LDBL_MAX * x;
}
strong_alias (__ieee754_exp2l, __exp2l_finite)

15
math/libm-test.inc
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@ -3127,6 +3127,21 @@ exp2_test (void)
TEST_f_f (exp2, -1e6, 0);
TEST_f_f (exp2, 0.75L, 1.68179283050742908606225095246642979L);
TEST_f_f (exp2, 100.5, 1.792728671193156477399422023278661496394e+30L);
TEST_f_f (exp2, 127, 0x1p127);
TEST_f_f (exp2, -149, 0x1p-149);
#ifndef TEST_FLOAT
TEST_f_f (exp2, 1000.25, 1.274245659452564874772384918171765416737e+301L);
TEST_f_f (exp2, 1023, 0x1p1023);
TEST_f_f (exp2, -1074, 0x1p-1074);
#endif
#if defined TEST_LDOUBLE && LDBL_MAX_EXP >= 16384
TEST_f_f (exp2, 16383, 0x1p16383L);
TEST_f_f (exp2, -16400, 0x1p-16400L);
#endif
END (exp2);
}