mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-26 12:41:05 +00:00
79 lines
2.3 KiB
C
79 lines
2.3 KiB
C
/* logb(). PowerPC/POWER7 version.
|
|
Copyright (C) 2012-2013 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
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
#include <math_ldbl_opt.h>
|
|
|
|
/* This implementation avoids FP to INT conversions by using VSX
|
|
bitwise instructions over FP values. */
|
|
|
|
static const double two1div52 = 2.220446049250313e-16; /* 1/2**52 */
|
|
static const double two10m1 = -1023.0; /* 2**10 -1 */
|
|
|
|
/* FP mask to extract the exponent. */
|
|
static const union {
|
|
unsigned long long mask;
|
|
double d;
|
|
} mask = { 0x7ff0000000000000ULL };
|
|
|
|
double
|
|
__logb (double x)
|
|
{
|
|
double ret;
|
|
|
|
if (__builtin_expect (x == 0.0, 0))
|
|
/* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */
|
|
return -1.0 / __builtin_fabs (x);
|
|
|
|
/* ret = x & 0x7ff0000000000000; */
|
|
asm (
|
|
"xxland %x0,%x1,%x2\n"
|
|
"fcfid %0,%0"
|
|
: "=f" (ret)
|
|
: "f" (x), "f" (mask.d));
|
|
/* ret = (ret >> 52) - 1023.0; */
|
|
ret = (ret * two1div52) + two10m1;
|
|
if (__builtin_expect (ret > -two10m1, 0))
|
|
/* Multiplication is used to set logb (+-INF) = INF. */
|
|
return (x * x);
|
|
else if (__builtin_expect (ret == two10m1, 0))
|
|
{
|
|
/* POSIX specifies that denormal numbers are treated as
|
|
though they were normalized. */
|
|
int32_t lx, ix;
|
|
int ma;
|
|
|
|
EXTRACT_WORDS (ix, lx, x);
|
|
if (ix == 0)
|
|
ma = __builtin_clz (lx) + 32;
|
|
else
|
|
ma = __builtin_clz (ix);
|
|
return (double) (-1023 - (ma - 12));
|
|
}
|
|
/* Test to avoid logb_downward (0.0) == -0.0. */
|
|
return ret == -0.0 ? 0.0 : ret;
|
|
}
|
|
weak_alias (__logb, logb)
|
|
#ifdef NO_LONG_DOUBLE
|
|
strong_alias (__logb, __logbl)
|
|
weak_alias (__logb, logbl)
|
|
#endif
|
|
|
|
#if LONG_DOUBLE_COMPAT (libm, GLIBC_2_0)
|
|
compat_symbol (libm, logb, logbl, GLIBC_2_0);
|
|
#endif
|