1 | /* Compute x * y + z as ternary operation. |
2 | Copyright (C) 2010-2017 Free Software Foundation, Inc. |
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 |
17 | License along with the GNU C Library; if not, see |
18 | <http://www.gnu.org/licenses/>. */ |
19 | |
20 | #include <math.h> |
21 | #include <fenv.h> |
22 | #include <ieee754.h> |
23 | #include <math_private.h> |
24 | |
25 | /* This implementation relies on double being more than twice as |
26 | precise as float and uses rounding to odd in order to avoid problems |
27 | with double rounding. |
28 | See a paper by Boldo and Melquiond: |
29 | http://www.lri.fr/~melquion/doc/08-tc.pdf */ |
30 | |
31 | float |
32 | __fmaf (float x, float y, float z) |
33 | { |
34 | fenv_t env; |
35 | |
36 | /* Multiplication is always exact. */ |
37 | double temp = (double) x * (double) y; |
38 | |
39 | /* Ensure correct sign of an exact zero result by performing the |
40 | addition in the original rounding mode in that case. */ |
41 | if (temp == -z) |
42 | return (float) temp + z; |
43 | |
44 | union ieee754_double u; |
45 | |
46 | libc_feholdexcept_setround (&env, FE_TOWARDZERO); |
47 | |
48 | /* Perform addition with round to odd. */ |
49 | u.d = temp + (double) z; |
50 | /* Ensure the addition is not scheduled after fetestexcept call. */ |
51 | math_force_eval (u.d); |
52 | |
53 | /* Reset rounding mode and test for inexact simultaneously. */ |
54 | int j = libc_feupdateenv_test (&env, FE_INEXACT) != 0; |
55 | |
56 | if ((u.ieee.mantissa1 & 1) == 0 && u.ieee.exponent != 0x7ff) |
57 | u.ieee.mantissa1 |= j; |
58 | |
59 | /* And finally truncation with round to nearest. */ |
60 | return (float) u.d; |
61 | } |
62 | #ifndef __fmaf |
63 | weak_alias (__fmaf, fmaf) |
64 | #endif |
65 | |