65 lines
2.1 KiB
C
65 lines
2.1 KiB
C
|
/* Get exponent of a floating-point value. PowerPC version.
|
||
|
|
Copyright (C) 2012-2022 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/dbl-64/s_logb.c>
|
||
|
|
#else
|
||
|
|
# include <math.h>
|
||
|
|
# include <math_private.h>
|
||
|
|
# include <math_ldbl_opt.h>
|
||
|
|
# include <libm-alias-double.h>
|
||
|
|
|
||
|
|
/* This implementation avoids FP to INT conversions by using VSX
|
||
|
|
bitwise instructions over FP values. */
|
||
|
|
double
|
||
|
|
__logb (double x)
|
||
|
|
{
|
||
|
|
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 * 0x1p-52) - 1023.0;
|
||
|
|
if (ret > 1023.0)
|
||
|
|
/* Multiplication is used to set logb (+-INF) = INF. */
|
||
|
|
return (x * x);
|
||
|
|
else if (ret == -1023.0)
|
||
|
|
{
|
||
|
|
/* POSIX specifies that denormal numbers are treated as
|
||
|
|
though they were normalized. */
|
||
|
|
int64_t ix;
|
||
|
|
EXTRACT_WORDS64 (ix, x);
|
||
|
|
ix &= UINT64_C (0x7fffffffffffffff);
|
||
|
|
return (double) (-1023 - (__builtin_clzll (ix) - 12));
|
||
|
|
}
|
||
|
|
/* Test to avoid logb_downward (0.0) == -0.0. */
|
||
|
|
return ret == -0.0 ? 0.0 : ret;
|
||
|
|
}
|
||
|
|
# ifndef __logb
|
||
|
|
libm_alias_double (__logb, logb)
|
||
|
|
# endif
|
||
|
|
#endif
|