projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| 777b1eea | 1 | /* logb(). PowerPC/POWER7 version. |
| b168057a | 2 | Copyright (C) 2012-2015 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 | ||
| 45470df3 | 19 | #include <math_ldbl_opt.h> |
| 777b1eea AZ |
20 | |
| 21 | /* This implementation avoids FP to INT conversions by using VSX | |
| 22 | bitwise instructions over FP values. */ | |
| 23 | ||
| 24 | static const double two1div52 = 2.220446049250313e-16; /* 1/2**52 */ | |
| 25 | static const double two10m1 = -1023.0; /* 2**10 -1 */ | |
| 26 | ||
| 27 | /* FP mask to extract the exponent. */ | |
| 28 | static const union { | |
| 29 | unsigned long long mask; | |
| 30 | double d; | |
| 31 | } mask = { 0x7ff0000000000000ULL }; | |
| 32 | ||
| 33 | double | |
| 34 | __logb (double x) | |
| 35 | { | |
| 36 | double ret; | |
| 37 | ||
| 38 | if (__builtin_expect (x == 0.0, 0)) | |
| 39 | /* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */ | |
| 40 | return -1.0 / __builtin_fabs (x); | |
| 41 | ||
| 42 | /* ret = x & 0x7ff0000000000000; */ | |
| 43 | asm ( | |
| 44 | "xxland %x0,%x1,%x2\n" | |
| 45 | "fcfid %0,%0" | |
| 46 | : "=f" (ret) | |
| 47 | : "f" (x), "f" (mask.d)); | |
| 48 | /* ret = (ret >> 52) - 1023.0; */ | |
| 49 | ret = (ret * two1div52) + two10m1; | |
| 50 | if (__builtin_expect (ret > -two10m1, 0)) | |
| 51 | /* Multiplication is used to set logb (+-INF) = INF. */ | |
| 52 | return (x * x); | |
| 53 | else if (__builtin_expect (ret == two10m1, 0)) | |
| 54 | { | |
| 55 | /* POSIX specifies that denormal numbers are treated as | |
| 56 | though they were normalized. */ | |
| 57 | int32_t lx, ix; | |
| 25dbcb27 | 58 | int ma; |
| 777b1eea | 59 | |
| 25dbcb27 AS |
60 | EXTRACT_WORDS (ix, lx, x); |
| 61 | if (ix == 0) | |
| 62 | ma = __builtin_clz (lx) + 32; | |
| 63 | else | |
| 64 | ma = __builtin_clz (ix); | |
| 65 | return (double) (-1023 - (ma - 12)); | |
| 777b1eea AZ |
66 | } |
| 67 | /* Test to avoid logb_downward (0.0) == -0.0. */ | |
| 68 | return ret == -0.0 ? 0.0 : ret; | |
| 69 | } | |
| 777b1eea | 70 | weak_alias (__logb, logb) |
| 777b1eea AZ |
71 | #ifdef NO_LONG_DOUBLE |
| 72 | strong_alias (__logb, __logbl) | |
| 73 | weak_alias (__logb, logbl) | |
| 74 | #endif | |
| 45470df3 AZ |
75 | |
| 76 | #if LONG_DOUBLE_COMPAT (libm, GLIBC_2_0) | |
| 77 | compat_symbol (libm, logb, logbl, GLIBC_2_0); | |
| 78 | #endif |