projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| 5e908464 | 1 | /* Compute x * y + z as ternary operation. |
| b168057a | 2 | Copyright (C) 2010-2015 Free Software Foundation, Inc. |
| 5e908464 JJ |
3 | This file is part of the GNU C Library. |
| 4 | Contributed by Jakub Jelinek <jakub@redhat.com>, 2010. | |
| 5 | ||
| 6 | The GNU C Library is free software; you can redistribute it and/or | |
| 7 | modify it under the terms of the GNU Lesser General Public | |
| 8 | License as published by the Free Software Foundation; either | |
| 9 | version 2.1 of the License, or (at your option) any later version. | |
| 10 | ||
| 11 | The GNU C Library is distributed in the hope that it will be useful, | |
| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
| 14 | Lesser General Public License for more details. | |
| 15 | ||
| 16 | You should have received a copy of the GNU Lesser General Public | |
| 59ba27a6 PE |
17 | License along with the GNU C Library; if not, see |
| 18 | <http://www.gnu.org/licenses/>. */ | |
| 5e908464 JJ |
19 | |
| 20 | #include <math.h> | |
| 21 | #include <fenv.h> | |
| 22 | #include <ieee754.h> | |
| 23 | ||
| 24 | /* This implementation relies on long double being more than twice as | |
| 25 | precise as double and uses rounding to odd in order to avoid problems | |
| 26 | with double rounding. | |
| 27 | See a paper by Boldo and Melquiond: | |
| 28 | http://www.lri.fr/~melquion/doc/08-tc.pdf */ | |
| 29 | ||
| 30 | double | |
| 31 | __fma (double x, double y, double z) | |
| 32 | { | |
| 33 | fenv_t env; | |
| 34 | /* Multiplication is always exact. */ | |
| 35 | long double temp = (long double) x * (long double) y; | |
| 8ec5b013 JM |
36 | |
| 37 | /* Ensure correct sign of an exact zero result by performing the | |
| 38 | addition in the original rounding mode in that case. */ | |
| 39 | if (temp == -z) | |
| 40 | return (double) temp + z; | |
| 41 | ||
| 5e908464 JJ |
42 | union ieee854_long_double u; |
| 43 | feholdexcept (&env); | |
| 44 | fesetround (FE_TOWARDZERO); | |
| 45 | /* Perform addition with round to odd. */ | |
| 46 | u.d = temp + (long double) z; | |
| 47 | if ((u.ieee.mantissa3 & 1) == 0 && u.ieee.exponent != 0x7fff) | |
| 48 | u.ieee.mantissa3 |= fetestexcept (FE_INEXACT) != 0; | |
| 49 | feupdateenv (&env); | |
| 50 | /* And finally truncation with round to nearest. */ | |
| 51 | return (double) u.d; | |
| 52 | } | |
| 53 | #ifndef __fma | |
| 54 | weak_alias (__fma, fma) | |
| 55 | #endif |