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cb864fe0ec
When libm functions return a NaN: if it is for NaN input, it should be
computed from that input (e.g. adding it to itself), so that payloads
are propagated and signaling NaNs quieted, while if it is for non-NaN
input, it should be produced by a computation such as
(x - x) / (x - x), which raises "invalid" at the same time as
producing an appropriate NaN, so avoiding any need for a call to
feraiseexcept.
Various libm functions, however, call __nan ("") (or __nanf or __nanl)
to determine the NaN to return, together with using feraiseexcept
(FE_INVALID) to raise the exception. sysdeps/generic/math_private.h
has an optimization for those functions with constant "" argument so
this doesn't actually involve a call to the __nan function, but it is
still not the preferred approach for producing NaNs. (The optimized
code also always uses the NAN macro, i.e. produces a default NaN for
float converted to whatever the target type is, and on some
architectures that may not be the same as the preferred default NaN
for double or long double.)
This patch fixes the scalb functions to use the conventional method of
generating NaNs and raising "invalid" with an appropriate
computation. (Most instances of this issue are in the complex
functions, where it can more readily be fixed once they have been made
type-generic and so only a third as many places need fixing. Some of
the complex functions use __nan ("") + __nan (""), where the addition
serves no purpose whatsoever.)
Tested for x86_64 and x86.
* math/e_scalb.c: Do not include <fenv.h>.
(invalid_fn): Do calculation resulting in NaN instead of raising
FE_INVALID and returning a NaN explicitly.
* math/e_scalbf.c: Do not include <fenv.h>.
(invalid_fn): Do calculation resulting in NaN instead of raising
FE_INVALID and returning a NaN explicitly.
* math/e_scalbl.c: Do not include <fenv.h>.
(invalid_fn): Do calculation resulting in NaN instead of raising
FE_INVALID and returning a NaN explicitly.
55 lines
1.5 KiB
C
55 lines
1.5 KiB
C
/* Copyright (C) 2011-2016 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@gmail.com>, 2011.
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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 double
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__attribute__ ((noinline))
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invalid_fn (double x, double fn)
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{
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if (__rint (fn) != fn)
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return (fn - fn) / (fn - fn);
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else if (fn > 65000.0)
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return __scalbn (x, 65000);
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else
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return __scalbn (x,-65000);
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}
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double
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__ieee754_scalb (double x, double fn)
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{
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if (__glibc_unlikely (isnan (x)))
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return x * fn;
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if (__glibc_unlikely (!isfinite (fn)))
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{
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if (isnan (fn) || fn > 0.0)
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return x * fn;
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if (x == 0.0)
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return x;
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return x / -fn;
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}
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if (__glibc_unlikely (fabs (fn) >= 0x1p31 || (double) (int) fn != fn))
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return invalid_fn (x, fn);
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return __scalbn (x, (int) fn);
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}
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strong_alias (__ieee754_scalb, __scalb_finite)
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