| 1 | /* Compute x * y + z as ternary operation. |
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| 2 | Copyright (C) 2010-2022 Free Software Foundation, Inc. |
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| 3 | This file is part of the GNU C Library. |
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| 4 | |
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| 5 | The GNU C Library is free software; you can redistribute it and/or |
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| 6 | modify it under the terms of the GNU Lesser General Public |
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| 7 | License as published by the Free Software Foundation; either |
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| 8 | version 2.1 of the License, or (at your option) any later version. |
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| 9 | |
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| 10 | The GNU C Library is distributed in the hope that it will be useful, |
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 13 | Lesser General Public License for more details. |
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| 14 | |
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| 15 | You should have received a copy of the GNU Lesser General Public |
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| 16 | License along with the GNU C Library; if not, see |
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| 17 | <https://www.gnu.org/licenses/>. */ |
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| 18 | |
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| 19 | #define NO_MATH_REDIRECT |
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| 20 | #define dfmal __hide_dfmal |
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| 21 | #define f32xfmaf64 __hide_f32xfmaf64 |
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| 22 | #include <math.h> |
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| 23 | #undef dfmal |
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| 24 | #undef f32xfmaf64 |
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| 25 | #include <fenv.h> |
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| 26 | #include <ieee754.h> |
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| 27 | #include <libm-alias-double.h> |
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| 28 | #include <math-narrow-alias.h> |
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| 29 | #include <math-use-builtins.h> |
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| 30 | |
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| 31 | /* This implementation relies on long double being more than twice as |
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| 32 | precise as double and uses rounding to odd in order to avoid problems |
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| 33 | with double rounding. |
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| 34 | See a paper by Boldo and Melquiond: |
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| 35 | http://www.lri.fr/~melquion/doc/08-tc.pdf */ |
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| 36 | |
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| 37 | double |
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| 38 | __fma (double x, double y, double z) |
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| 39 | { |
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| 40 | #if USE_FMA_BUILTIN |
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| 41 | return __builtin_fma (x, y, z); |
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| 42 | #else |
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| 43 | fenv_t env; |
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| 44 | /* Multiplication is always exact. */ |
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| 45 | long double temp = (long double) x * (long double) y; |
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| 46 | |
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| 47 | /* Ensure correct sign of an exact zero result by performing the |
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| 48 | addition in the original rounding mode in that case. */ |
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| 49 | if (temp == -z) |
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| 50 | return (double) temp + z; |
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| 51 | |
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| 52 | union ieee854_long_double u; |
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| 53 | feholdexcept (envp: &env); |
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| 54 | fesetround (FE_TOWARDZERO); |
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| 55 | /* Perform addition with round to odd. */ |
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| 56 | u.d = temp + (long double) z; |
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| 57 | if ((u.ieee.mantissa3 & 1) == 0 && u.ieee.exponent != 0x7fff) |
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| 58 | u.ieee.mantissa3 |= fetestexcept (FE_INEXACT) != 0; |
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| 59 | feupdateenv (envp: &env); |
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| 60 | /* And finally truncation with round to nearest. */ |
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| 61 | return (double) u.d; |
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| 62 | #endif /* ! USE_FMA_BUILTIN */ |
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| 63 | } |
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| 64 | #ifndef __fma |
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| 65 | libm_alias_double (__fma, fma) |
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| 66 | libm_alias_double_narrow (__fma, fma) |
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| 67 | #endif |
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| 68 | |
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