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4fea2cda61
The generic fdim implementations have unnecessarily complicated code, using fpclassify to determine whether the arguments are NaNs, subtracting NaNs if so and otherwise subtracting the non-NaN arguments if not (x <= y), then using fpclassify on the result to see if it is infinite. This patch simplifies the code. Instead of handling NaNs separately, it suffices to use an unordered comparison with islessequal (x, y) to determine whether to return zero, and otherwise NaNs can go through the same subtraction as non-NaN arguments; no explicit tests for NaN are needed at all. Then, isinf instead of fpclassify can be used to determine whether to set errno (in the normal non-overflow case, only one classification will need to occur, unlike the three in the previous code, of which two occurred even if returning zero, because the result will not be infinite in the normal case). The resulting logic is essentially the same as that in the powerpc version, except that the powerpc version is missing errno setting and uses <= not islessequal, so relying on <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58684>, the GCC bug that unordered comparison instructions are wrongly used on powerpc for ordered comparisons. The compiled code for fdim and fdimf on x86_64 is less than half the size of the previous code. Tested for x86_64. * math/s_fdim.c (__fdim): Use islessequal and isinf instead of fpclassify. * math/s_fdimf.c (__fdimf): Likewise. * math/s_fdiml.c (__fdiml): Likewise.
36 lines
1.1 KiB
C
36 lines
1.1 KiB
C
/* Return positive difference between arguments.
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Copyright (C) 1997-2016 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 <errno.h>
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#include <math.h>
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long double
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__fdiml (long double x, long double y)
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{
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if (islessequal (x, y))
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return 0.0f;
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long double r = x - y;
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if (isinf (r) && !isinf (x) && !isinf (y))
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__set_errno (ERANGE);
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return r;
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}
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weak_alias (__fdiml, fdiml)
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