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/* logbf(). PowerPC/POWER7 version.
Copyright (C) 2012-2018 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"
#include <libm-alias-float.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;
}
libm_alias_float (__logb, logb)
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