glibc/math/e_scalb.c

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/* Copyright (C) 2011-2018 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@gmail.com>, 2011.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
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#include <math.h>
#include <math_private.h>
static double
__attribute__ ((noinline))
invalid_fn (double x, double fn)
{
if (__rint (fn) != fn)
Do not call __nan in scalb functions. 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.
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return (fn - fn) / (fn - fn);
else if (fn > 65000.0)
return __scalbn (x, 65000);
else
return __scalbn (x,-65000);
}
double
__ieee754_scalb (double x, double fn)
{
if (__glibc_unlikely (isnan (x)))
return x * fn;
if (__glibc_unlikely (!isfinite (fn)))
{
if (isnan (fn) || fn > 0.0)
return x * fn;
if (x == 0.0)
return x;
return x / -fn;
}
if (__glibc_unlikely (fabs (fn) >= 0x1p31 || (double) (int) fn != fn))
return invalid_fn (x, fn);
return __scalbn (x, (int) fn);
}
strong_alias (__ieee754_scalb, __scalb_finite)