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777b1eea | 1 | /* logbl(). PowerPC/POWER7 version. |
bfff8b1b | 2 | Copyright (C) 2012-2017 Free Software Foundation, Inc. |
777b1eea AZ |
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 | <http://www.gnu.org/licenses/>. */ | |
18 | ||
19 | #include <math.h> | |
20 | #include <math_private.h> | |
21 | #include <math_ldbl_opt.h> | |
22 | ||
23 | /* This implementation avoids FP to INT conversions by using VSX | |
24 | bitwise instructions over FP values. */ | |
25 | ||
26 | static const double two1div52 = 2.220446049250313e-16; /* 1/2**52 */ | |
27 | static const double two10m1 = -1023.0; /* 2**10 -1 */ | |
28 | ||
29 | /* FP mask to extract the exponent. */ | |
30 | static const union { | |
31 | unsigned long long mask; | |
32 | double d; | |
33 | } mask = { 0x7ff0000000000000ULL }; | |
34 | ||
35 | long double | |
36 | __logbl (long double x) | |
37 | { | |
4ebd120c | 38 | double xh; |
777b1eea AZ |
39 | double ret; |
40 | ||
41 | if (__builtin_expect (x == 0.0L, 0)) | |
42 | /* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */ | |
43 | return -1.0L / __builtin_fabsl (x); | |
44 | ||
4ebd120c | 45 | xh = ldbl_high (x); |
777b1eea AZ |
46 | /* ret = x & 0x7ff0000000000000; */ |
47 | asm ( | |
48 | "xxland %x0,%x1,%x2\n" | |
49 | "fcfid %0,%0" | |
50 | : "=f" (ret) | |
51 | : "f" (xh), "f" (mask.d)); | |
52 | /* ret = (ret >> 52) - 1023.0; */ | |
53 | ret = (ret * two1div52) + two10m1; | |
54 | if (__builtin_expect (ret > -two10m1, 0)) | |
55 | /* Multiplication is used to set logb (+-INF) = INF. */ | |
56 | return (xh * xh); | |
57 | else if (__builtin_expect (ret == two10m1, 0)) | |
58 | { | |
25dbcb27 AS |
59 | /* POSIX specifies that denormal number is treated as |
60 | though it were normalized. */ | |
4ebd120c | 61 | int64_t hx; |
777b1eea | 62 | |
4ebd120c | 63 | EXTRACT_WORDS64 (hx, xh); |
25dbcb27 | 64 | return (long double) (-1023 - (__builtin_clzll (hx) - 12)); |
777b1eea AZ |
65 | } |
66 | /* Test to avoid logb_downward (0.0) == -0.0. */ | |
67 | return ret == -0.0 ? 0.0 : ret; | |
68 | } | |
2d9470b2 | 69 | #ifndef __logbl |
777b1eea | 70 | long_double_symbol (libm, __logbl, logbl); |
2d9470b2 | 71 | #endif |