1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
|
/* logb(). PowerPC/POWER7 version.
Copyright (C) 2012-2017 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);
ix &= 0x7fffffff;
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
|
