1 /* Get exponent of a floating-point value. PowerPC version.
2 Copyright (C) 2012-2022 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 /* ISA 2.07 provides fast GPR to FP instruction (mfvsr{d,wz}) which make
20 generic implementation faster. */
21 #if defined(_ARCH_PWR8) || !defined(_ARCH_PWR7)
22 # include <./sysdeps/ieee754/ldbl-128ibm/s_logbl.c>
23 #else
24 # include <math.h>
25 # include <math_private.h>
26 # include <math_ldbl_opt.h>
27
28 /* This implementation avoids FP to INT conversions by using VSX
29 bitwise instructions over FP values. */
30 long double
__logbl(long double x)31 __logbl (long double x)
32 {
33 double xh, xl;
34 double ret;
35 int64_t hx;
36
37 if (__glibc_unlikely (x == 0.0))
38 /* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */
39 return -1.0L / __builtin_fabsl (x);
40
41 ldbl_unpack (x, &xh, &xl);
42 EXTRACT_WORDS64 (hx, xh);
43
44 /* Mask to extract the exponent. */
45 asm ("xxland %x0,%x1,%x2\n"
46 "fcfid %0,%0"
47 : "=d" (ret)
48 : "d" (xh), "d" (0x7ff0000000000000ULL));
49 ret = (ret * 0x1p-52) - 1023.0;
50 if (ret > 1023.0)
51 /* Multiplication is used to set logb (+-INF) = INF. */
52 return (xh * xh);
53 else if (ret == -1023.0)
54 {
55 /* POSIX specifies that denormal number is treated as
56 though it were normalized. */
57 return (long double) (- (__builtin_clzll (hx & 0x7fffffffffffffffLL) \
58 - 12) - 1023);
59 }
60 else if ((hx & 0x000fffffffffffffLL) == 0)
61 {
62 /* If the high part is a power of 2, and the low part is nonzero
63 with the opposite sign, the low part affects the
64 exponent. */
65 int64_t lx, rhx;
66 EXTRACT_WORDS64 (lx, xl);
67 rhx = (hx & 0x7ff0000000000000LL) >> 52;
68 if ((hx ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
69 rhx--;
70 return (long double) (rhx - 1023);
71 }
72 /* Test to avoid logb_downward (0.0) == -0.0. */
73 return ret == -0.0 ? 0.0 : ret;
74 }
75 # ifndef __logbl
76 long_double_symbol (libm, __logbl, logbl);
77 # endif
78 #endif
79