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ce8fc784e6
Various remquo implementations produce a zero remainder with the wrong sign (a zero remainder should always have the sign of the first argument, as specified in IEEE 754) in round-downward mode, resulting from the sign of 0 - 0. This patch checks for zero results and fixes their sign accordingly. Tested for x86_64, x86, mips64 and powerpc. [BZ #17987] * sysdeps/ieee754/dbl-64/s_remquo.c (__remquo): Ensure sign of zero result does not depend on the sign resulting from subtraction. * sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c (__remquo): Likewise. * sysdeps/ieee754/flt-32/s_remquof.c (__remquof): Likewise. * sysdeps/ieee754/ldbl-128/s_remquol.c (__remquol): Likewise. * sysdeps/ieee754/ldbl-128ibm/s_remquol.c (__remquol): Likewise. * sysdeps/ieee754/ldbl-96/s_remquol.c (__remquol): Likewise. * math/libm-test.inc (remquo_test_data): Add more tests.
116 lines
2.5 KiB
C
116 lines
2.5 KiB
C
/* Compute remainder and a congruent to the quotient.
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Copyright (C) 1997-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
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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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static const double zero = 0.0;
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double
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__remquo (double x, double y, int *quo)
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{
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int32_t hx, hy;
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u_int32_t sx, lx, ly;
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int cquo, qs;
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EXTRACT_WORDS (hx, lx, x);
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EXTRACT_WORDS (hy, ly, y);
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sx = hx & 0x80000000;
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qs = sx ^ (hy & 0x80000000);
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hy &= 0x7fffffff;
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hx &= 0x7fffffff;
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/* Purge off exception values. */
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if ((hy | ly) == 0)
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return (x * y) / (x * y); /* y = 0 */
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if ((hx >= 0x7ff00000) /* x not finite */
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|| ((hy >= 0x7ff00000) /* p is NaN */
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&& (((hy - 0x7ff00000) | ly) != 0)))
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return (x * y) / (x * y);
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if (hy <= 0x7fbfffff)
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x = __ieee754_fmod (x, 8 * y); /* now x < 8y */
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if (((hx - hy) | (lx - ly)) == 0)
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{
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*quo = qs ? -1 : 1;
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return zero * x;
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}
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x = fabs (x);
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y = fabs (y);
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cquo = 0;
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if (hy <= 0x7fcfffff && x >= 4 * y)
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{
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x -= 4 * y;
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cquo += 4;
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}
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if (hy <= 0x7fdfffff && x >= 2 * y)
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{
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x -= 2 * y;
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cquo += 2;
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}
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if (hy < 0x00200000)
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{
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if (x + x > y)
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{
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x -= y;
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++cquo;
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if (x + x >= y)
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{
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x -= y;
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++cquo;
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}
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}
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}
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else
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{
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double y_half = 0.5 * y;
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if (x > y_half)
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{
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x -= y;
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++cquo;
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if (x >= y_half)
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{
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x -= y;
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++cquo;
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}
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}
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}
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*quo = qs ? -cquo : cquo;
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/* Ensure correct sign of zero result in round-downward mode. */
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if (x == 0.0)
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x = 0.0;
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if (sx)
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x = -x;
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return x;
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}
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weak_alias (__remquo, remquo)
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#ifdef NO_LONG_DOUBLE
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strong_alias (__remquo, __remquol)
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weak_alias (__remquo, remquol)
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#endif
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