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03d95bd483
This patch fixes the remaining part of bug 16560, spurious underflows from exp2 of arguments close to 0 (when the result is close to 1, so should not underflow), by just using 1+x instead of a more complicated calculation when the argument is sufficiently small. Tested for x86_64, x86 and mips64. [BZ #16560] * math/e_exp2l.c [LDBL_MANT_DIG == 106] (LDBL_EPSILON): Undefine and redefine. (__ieee754_exp2l): Do not multiply small fractional parts by M_LN2l. * sysdeps/i386/fpu/e_exp2l.S (__ieee754_exp2l): Just add 1 to small argument. * sysdeps/ieee754/dbl-64/e_exp2.c (__ieee754_exp2): Likewise. * sysdeps/ieee754/flt-32/e_exp2f.c (__ieee754_exp2f): Likewise. * sysdeps/x86_64/fpu/e_exp2l.S (__ieee754_exp2l): Likewise. * math/auto-libm-test-in: Add more tests of exp2. * math/auto-libm-test-out: Regenerated.
59 lines
1.7 KiB
C
59 lines
1.7 KiB
C
/* Compute 2^x.
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Copyright (C) 2012-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <math.h>
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#include <math_private.h>
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#include <float.h>
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/* To avoid spurious underflows, use this definition to treat IBM long
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double as approximating an IEEE-style format. */
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#if LDBL_MANT_DIG == 106
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# undef LDBL_EPSILON
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# define LDBL_EPSILON 0x1p-106L
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#endif
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long double
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__ieee754_exp2l (long double x)
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{
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if (__glibc_likely (isless (x, (long double) LDBL_MAX_EXP)))
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{
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if (__builtin_expect (isgreaterequal (x, (long double) (LDBL_MIN_EXP
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- LDBL_MANT_DIG
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- 1)), 1))
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{
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int intx = (int) x;
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long double fractx = x - intx;
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if (fabsl (fractx) < LDBL_EPSILON / 4.0L)
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return __scalbnl (1.0L + fractx, intx);
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return __scalbnl (__ieee754_expl (M_LN2l * fractx), intx);
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}
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else
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{
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/* Underflow or exact zero. */
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if (__isinfl (x))
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return 0;
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else
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return LDBL_MIN * LDBL_MIN;
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}
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}
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else
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/* Infinity, NaN or overflow. */
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return LDBL_MAX * x;
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}
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strong_alias (__ieee754_exp2l, __exp2l_finite)
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