mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-25 04:01:10 +00:00
61 lines
2.0 KiB
C
61 lines
2.0 KiB
C
/* logbf(). PowerPC/POWER7 version.
|
|
Copyright (C) 2012-2016 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_private.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 */
|
|
static const double two7m1 = -127.0; /* -2**7 + 1 */
|
|
|
|
/* FP mask to extract the exponent. */
|
|
static const union {
|
|
unsigned long long mask;
|
|
double d;
|
|
} mask = { 0x7ff0000000000000ULL };
|
|
|
|
float
|
|
__logbf (float x)
|
|
{
|
|
/* VSX operation are all done internally as double. */
|
|
double ret;
|
|
|
|
if (__builtin_expect (x == 0.0, 0))
|
|
/* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */
|
|
return -1.0 / __builtin_fabsf (x);
|
|
|
|
/* ret = x & 0x7f800000; */
|
|
asm (
|
|
"xxland %x0,%x1,%x2\n"
|
|
"fcfid %0,%0"
|
|
: "=f"(ret)
|
|
: "f" (x), "f" (mask.d));
|
|
/* ret = (ret >> 52) - 1023.0, since ret is double. */
|
|
ret = (ret * two1div52) + two10m1;
|
|
if (__builtin_expect (ret > -two7m1, 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;
|
|
}
|
|
weak_alias (__logbf, logbf)
|