| /* Compute full X * Y for double type. |
| Copyright (C) 2013-2018 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #ifndef _MUL_SPLIT_H |
| #define _MUL_SPLIT_H |
| |
| #include <float.h> |
| |
| /* Calculate X * Y exactly and store the result in *HI + *LO. It is |
| given that the values are small enough that no overflow occurs and |
| large enough (or zero) that no underflow occurs. */ |
| |
| static void |
| mul_split (double *hi, double *lo, double x, double y) |
| { |
| #ifdef __FP_FAST_FMA |
| /* Fast built-in fused multiply-add. */ |
| *hi = x * y; |
| *lo = __builtin_fma (x, y, -*hi); |
| #else |
| /* Apply Dekker's algorithm. */ |
| *hi = x * y; |
| # define C ((1 << (DBL_MANT_DIG + 1) / 2) + 1) |
| double x1 = x * C; |
| double y1 = y * C; |
| # undef C |
| x1 = (x - x1) + x1; |
| y1 = (y - y1) + y1; |
| double x2 = x - x1; |
| double y2 = y - y1; |
| *lo = (((x1 * y1 - *hi) + x1 * y2) + x2 * y1) + x2 * y2; |
| #endif |
| } |
| |
| #endif /* _MUL_SPLIT_H */ |
