51 lines
1.6 KiB
C
51 lines
1.6 KiB
C
/* Compute full X * Y for long 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_SPLITL_H
|
|
#define _MUL_SPLITL_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 inline void
|
|
mul_splitl (long double *hi, long double *lo, long double x, long double y)
|
|
{
|
|
#ifdef __FP_FAST_FMAL
|
|
/* Fast built-in fused multiply-add. */
|
|
*hi = x * y;
|
|
*lo = __builtin_fmal (x, y, -*hi);
|
|
#else
|
|
/* Apply Dekker's algorithm. */
|
|
*hi = x * y;
|
|
# define C ((1LL << (LDBL_MANT_DIG + 1) / 2) + 1)
|
|
long double x1 = x * C;
|
|
long double y1 = y * C;
|
|
# undef C
|
|
x1 = (x - x1) + x1;
|
|
y1 = (y - y1) + y1;
|
|
long double x2 = x - x1;
|
|
long double y2 = y - y1;
|
|
*lo = (((x1 * y1 - *hi) + x1 * y2) + x2 * y1) + x2 * y2;
|
|
#endif
|
|
}
|
|
|
|
#endif /* _MUL_SPLITL_H */
|