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/* Get exponent of a floating-point value. PowerPC version.
Copyright (C) 2012-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
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
<https://www.gnu.org/licenses/>. */
/* ISA 2.07 provides fast GPR to FP instruction (mfvsr{d,wz}) which make
generic implementation faster. */
#if defined(_ARCH_PWR8) || !defined(_ARCH_PWR7)
# include <sysdeps/ieee754/flt-32/s_logbf.c>
#else
# include <math.h>
# include <libm-alias-float.h>
/* This implementation avoids FP to INT conversions by using VSX
bitwise instructions over FP values. */
float
__logbf (float x)
{
/* VSX operation are all done internally as double. */
double ret;
if (__glibc_unlikely (x == 0.0))
/* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */
return -1.0 / fabs (x);
/* mask to extract the exponent. */
asm ("xxland %x0,%x1,%x2\n"
"fcfid %0,%0"
: "=d"(ret)
: "d" (x), "d" (0x7ff0000000000000ULL));
/* ret = (ret >> 52) - 1023.0, since ret is double. */
ret = (ret * 0x1p-52) - 1023.0;
if (ret > 127.0)
/* Multiplication is used to set logb (+-INF) = INF. */
return (x * x);
/* Since operations are done with double we don't need
additional tests for subnormal numbers.
The test is to avoid logb_downward (0.0) == -0.0. */
return ret == -0.0 ? 0.0 : ret;
}
# ifndef __logbf
libm_alias_float (__logb, logb)
# endif
#endif
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