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/* origin: FreeBSD /usr/src/lib/msun/src/s_fmaf.c */
/*-
* Copyright (c) 2005-2011 David Schultz <das@FreeBSD.ORG>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <fenv.h>
#include "libm.h"
/*
* Fused multiply-add: Compute x * y + z with a single rounding error.
*
* A double has more than twice as much precision than a float, so
* direct double-precision arithmetic suffices, except where double
* rounding occurs.
*/
float fmaf(float x, float y, float z)
{
double xy, result;
uint32_t hr, lr;
xy = (double)x * y;
result = xy + z;
EXTRACT_WORDS(hr, lr, result);
/* Common case: The double precision result is fine. */
if ((lr & 0x1fffffff) != 0x10000000 || /* not a halfway case */
(hr & 0x7ff00000) == 0x7ff00000 || /* NaN */
result - xy == z || /* exact */
fegetround() != FE_TONEAREST) /* not round-to-nearest */
return (result);
/*
* If result is inexact, and exactly halfway between two float values,
* we need to adjust the low-order bit in the direction of the error.
*/
#ifdef FE_TOWARDZERO
fesetround(FE_TOWARDZERO);
#endif
volatile double vxy = xy; /* XXX work around gcc CSE bug */
double adjusted_result = vxy + z;
fesetround(FE_TONEAREST);
if (result == adjusted_result)
SET_LOW_WORD(adjusted_result, lr + 1);
return (adjusted_result);
}
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