1 /* Compute full X * Y for long double type.
2 Copyright (C) 2013-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
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.
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.
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/>. */
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. */
29 mul_splitl (long double *hi, long double *lo, long double x, long double y)
32 /* Fast built-in fused multiply-add. */
34 *lo = __builtin_fmal (x, y, -*hi);
36 /* Apply Dekker's algorithm. */
38 # define C ((1LL << (LDBL_MANT_DIG + 1) / 2) + 1)
39 long double x1 = x * C;
40 long double y1 = y * C;
44 long double x2 = x - x1;
45 long double y2 = y - y1;
46 *lo = (((x1 * y1 - *hi) + x1 * y2) + x2 * y1) + x2 * y2;
50 #endif /* _MUL_SPLITL_H */