2 * SPDX-License-Identifier: BSD-2-Clause
4 * Copyright (c) 2005-2011 David Schultz <das@FreeBSD.ORG>
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8 * modification, are permitted provided that the following conditions
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29 #include <sys/cdefs.h>
33 #include "math_private.h"
35 #ifdef USE_BUILTIN_FMAF
37 fmaf(float x, float y, float z)
39 return (__builtin_fmaf(x, y, z));
43 * Fused multiply-add: Compute x * y + z with a single rounding error.
45 * A double has more than twice as much precision than a float, so
46 * direct double-precision arithmetic suffices, except where double
50 fmaf(float x, float y, float z)
57 EXTRACT_WORDS(hr, lr, result);
58 /* Common case: The double precision result is fine. */
59 if ((lr & 0x1fffffff) != 0x10000000 || /* not a halfway case */
60 (hr & 0x7ff00000) == 0x7ff00000 || /* NaN */
61 result - xy == z || /* exact */
62 fegetround() != FE_TONEAREST) /* not round-to-nearest */
66 * If result is inexact, and exactly halfway between two float values,
67 * we need to adjust the low-order bit in the direction of the error.
69 fesetround(FE_TOWARDZERO);
70 volatile double vxy = xy; /* XXX work around gcc CSE bug */
71 double adjusted_result = vxy + z;
72 fesetround(FE_TONEAREST);
73 if (result == adjusted_result)
74 SET_LOW_WORD(adjusted_result, lr + 1);
75 return (adjusted_result);
77 #endif /* !USE_BUILTIN_FMAF */