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/* logbl(). PowerPC/POWER7 version.
Copyright (C) 2012-2019 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.h>
#include <math_private.h>
#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 };
long double
__logbl (long double x)
{
double xh, xl;
double ret;
int64_t hx;
if (__builtin_expect (x == 0.0L, 0))
/* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */
return -1.0L / __builtin_fabsl (x);
ldbl_unpack (x, &xh, &xl);
EXTRACT_WORDS64 (hx, xh);
/* ret = x & 0x7ff0000000000000; */
asm (
"xxland %x0,%x1,%x2\n"
"fcfid %0,%0"
: "=f" (ret)
: "f" (xh), "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 (xh * xh);
else if (__builtin_expect (ret == two10m1, 0))
{
/* POSIX specifies that denormal number is treated as
though it were normalized. */
return (long double) (- (__builtin_clzll (hx & 0x7fffffffffffffffLL) \
- 12) - 1023);
}
else if ((hx & 0x000fffffffffffffLL) == 0)
{
/* If the high part is a power of 2, and the low part is nonzero
with the opposite sign, the low part affects the
exponent. */
int64_t lx, rhx;
EXTRACT_WORDS64 (lx, xl);
rhx = (hx & 0x7ff0000000000000LL) >> 52;
if ((hx ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
rhx--;
return (long double) (rhx - 1023);
}
/* Test to avoid logb_downward (0.0) == -0.0. */
return ret == -0.0 ? 0.0 : ret;
}
#ifndef __logbl
long_double_symbol (libm, __logbl, logbl);
#endif
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