Rich Felker
2e77dc13f8
this is necessary to support archs where fenv is incomplete or unavailable (presently arm). fma, fmal, and the lrint family should work perfectly fine with this change; fmaf is slightly broken with respect to rounding as it depends on non-default rounding modes to do its work.
67 lines
2.5 KiB
C
67 lines
2.5 KiB
C
/* origin: FreeBSD /usr/src/lib/msun/src/s_fmaf.c */
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/*-
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* Copyright (c) 2005-2011 David Schultz <[email protected]>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <fenv.h>
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#include "libm.h"
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/*
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* Fused multiply-add: Compute x * y + z with a single rounding error.
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*
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* A double has more than twice as much precision than a float, so
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* direct double-precision arithmetic suffices, except where double
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* rounding occurs.
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*/
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float fmaf(float x, float y, float z)
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{
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double xy, result;
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uint32_t hr, lr;
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xy = (double)x * y;
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result = xy + z;
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EXTRACT_WORDS(hr, lr, result);
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/* Common case: The double precision result is fine. */
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if ((lr & 0x1fffffff) != 0x10000000 || /* not a halfway case */
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(hr & 0x7ff00000) == 0x7ff00000 || /* NaN */
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result - xy == z || /* exact */
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fegetround() != FE_TONEAREST) /* not round-to-nearest */
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return (result);
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/*
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* If result is inexact, and exactly halfway between two float values,
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* we need to adjust the low-order bit in the direction of the error.
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*/
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#ifdef FE_TOWARDZERO
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fesetround(FE_TOWARDZERO);
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#endif
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volatile double vxy = xy; /* XXX work around gcc CSE bug */
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double adjusted_result = vxy + z;
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fesetround(FE_TONEAREST);
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if (result == adjusted_result)
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SET_LOW_WORD(adjusted_result, lr + 1);
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return (adjusted_result);
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}
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