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a638de828d
This patch fixes spurious underflows from exp10 for arguments near 0 (part of bug 16560; that bug also includes spurious underflows from exp2, which are not fixed by this patch). The problem is underflows in the internal computation converting the exp10 argument to arguments for exp (with extra precision), and the fix is simply to return 1 early for arguments near enough to 0 (just as arguments with large enough magnitude have their own overflow / underflow logic at the start of the function). Tested x86_64 and x86 and ulps updated accordingly; also tested for powerpc32 and mips64 to validate the ldbl-128ibm and ldbl-128 changes. [BZ #16560] * sysdeps/ieee754/dbl-64/e_exp10.c (__ieee754_exp10): Return 1 for arguments close to 0. * sysdeps/ieee754/ldbl-128/e_exp10l.c (__ieee754_exp10l): Likewise. * sysdeps/ieee754/ldbl-128ibm/e_exp10l.c (__ieee754_exp10l): Likewise. * math/auto-libm-test-in: Add more tests of exp10. * math/auto-libm-test-out: Regenerated. * sysdeps/x86_64/fpu/libm-test-ulps: Update.
51 lines
1.6 KiB
C
51 lines
1.6 KiB
C
/* Copyright (C) 2012-2014 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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static const double log10_high = 0x2.4d7637p0;
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static const double log10_low = 0x7.6aaa2b05ba95cp-28;
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double
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__ieee754_exp10 (double arg)
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{
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int32_t lx;
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double arg_high, arg_low;
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double exp_high, exp_low;
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if (!__finite (arg))
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return __ieee754_exp (arg);
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if (arg < DBL_MIN_10_EXP - DBL_DIG - 10)
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return DBL_MIN * DBL_MIN;
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else if (arg > DBL_MAX_10_EXP + 1)
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return DBL_MAX * DBL_MAX;
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else if (fabs (arg) < 0x1p-56)
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return 1.0;
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GET_LOW_WORD (lx, arg);
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lx &= 0xf8000000;
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arg_high = arg;
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SET_LOW_WORD (arg_high, lx);
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arg_low = arg - arg_high;
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exp_high = arg_high * log10_high;
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exp_low = arg_high * log10_low + arg_low * M_LN10;
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return __ieee754_exp (exp_high) * __ieee754_exp (exp_low);
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}
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strong_alias (__ieee754_exp10, __exp10_finite)
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