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4482ff22 | 1 | /* Compute full X * Y for double type. |
04277e02 | 2 | Copyright (C) 2013-2019 Free Software Foundation, Inc. |
4482ff22 PM |
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 | <http://www.gnu.org/licenses/>. */ | |
18 | ||
19 | #ifndef _MUL_SPLIT_H | |
20 | #define _MUL_SPLIT_H | |
21 | ||
22 | #include <float.h> | |
23 | ||
24 | /* Calculate X * Y exactly and store the result in *HI + *LO. It is | |
25 | given that the values are small enough that no overflow occurs and | |
26 | large enough (or zero) that no underflow occurs. */ | |
27 | ||
28 | static void | |
29 | mul_split (double *hi, double *lo, double x, double y) | |
30 | { | |
31 | #ifdef __FP_FAST_FMA | |
32 | /* Fast built-in fused multiply-add. */ | |
33 | *hi = x * y; | |
34 | *lo = __builtin_fma (x, y, -*hi); | |
35 | #else | |
36 | /* Apply Dekker's algorithm. */ | |
37 | *hi = x * y; | |
38 | # define C ((1 << (DBL_MANT_DIG + 1) / 2) + 1) | |
39 | double x1 = x * C; | |
40 | double y1 = y * C; | |
41 | # undef C | |
42 | x1 = (x - x1) + x1; | |
43 | y1 = (y - y1) + y1; | |
44 | double x2 = x - x1; | |
45 | double y2 = y - y1; | |
46 | *lo = (((x1 * y1 - *hi) + x1 * y2) + x2 * y1) + x2 * y2; | |
47 | #endif | |
48 | } | |
49 | ||
50 | #endif /* _MUL_SPLIT_H */ |