1 | /* Compute x * y + z as ternary operation. |
2 | Copyright (C) 2010-2018 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 | #include <libm-alias-float.h> |
25 | |
26 | /* This implementation relies on double being more than twice as |
27 | precise as float and uses rounding to odd in order to avoid problems |
28 | with double rounding. |
29 | See a paper by Boldo and Melquiond: |
30 | http://www.lri.fr/~melquion/doc/08-tc.pdf */ |
31 | |
32 | float |
33 | __fmaf (float x, float y, float z) |
34 | { |
35 | fenv_t env; |
36 | |
37 | /* Multiplication is always exact. */ |
38 | double temp = (double) x * (double) y; |
39 | |
40 | /* Ensure correct sign of an exact zero result by performing the |
41 | addition in the original rounding mode in that case. */ |
42 | if (temp == -z) |
43 | return (float) temp + z; |
44 | |
45 | union ieee754_double u; |
46 | |
47 | libc_feholdexcept_setround (&env, FE_TOWARDZERO); |
48 | |
49 | /* Perform addition with round to odd. */ |
50 | u.d = temp + (double) z; |
51 | /* Ensure the addition is not scheduled after fetestexcept call. */ |
52 | math_force_eval (u.d); |
53 | |
54 | /* Reset rounding mode and test for inexact simultaneously. */ |
55 | int j = libc_feupdateenv_test (&env, FE_INEXACT) != 0; |
56 | |
57 | if ((u.ieee.mantissa1 & 1) == 0 && u.ieee.exponent != 0x7ff) |
58 | u.ieee.mantissa1 |= j; |
59 | |
60 | /* And finally truncation with round to nearest. */ |
61 | return (float) u.d; |
62 | } |
63 | #ifndef __fmaf |
64 | libm_alias_float (__fma, fma) |
65 | #endif |
66 | |