1/* Compute x * y + z as ternary operation.
2 Copyright (C) 2010-2023 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#define NO_MATH_REDIRECT
20#include <math.h>
21#include <fenv.h>
22#include <ieee754.h>
23#include <math-barriers.h>
24#include <fenv_private.h>
25#include <libm-alias-float.h>
26#include <math-use-builtins.h>
27
28/* This implementation relies on double being more than twice as
29 precise as float and uses rounding to odd in order to avoid problems
30 with double rounding.
31 See a paper by Boldo and Melquiond:
32 http://www.lri.fr/~melquion/doc/08-tc.pdf */
33
34float
35__fmaf (float x, float y, float z)
36{
37#if USE_FMAF_BUILTIN
38 return __builtin_fmaf (x, y, z);
39#else
40 /* Use generic implementation. */
41 fenv_t env;
42
43 /* Multiplication is always exact. */
44 double temp = (double) x * (double) y;
45
46 /* Ensure correct sign of an exact zero result by performing the
47 addition in the original rounding mode in that case. */
48 if (temp == -z)
49 return (float) temp + z;
50
51 union ieee754_double u;
52
53 libc_feholdexcept_setround (&env, FE_TOWARDZERO);
54
55 /* Perform addition with round to odd. */
56 u.d = temp + (double) z;
57 /* Ensure the addition is not scheduled after fetestexcept call. */
58 math_force_eval (u.d);
59
60 /* Reset rounding mode and test for inexact simultaneously. */
61 int j = libc_feupdateenv_test (&env, FE_INEXACT) != 0;
62
63 if ((u.ieee.mantissa1 & 1) == 0 && u.ieee.exponent != 0x7ff)
64 u.ieee.mantissa1 |= j;
65
66 /* And finally truncation with round to nearest. */
67 return (float) u.d;
68#endif /* ! USE_FMAF_BUILTIN */
69}
70#ifndef __fmaf
71libm_alias_float (__fma, fma)
72#endif
73