1 /* origin: FreeBSD /usr/src/lib/msun/src/s_fmaf.c */
3 * Copyright (c) 2005-2011 David Schultz <das@FreeBSD.ORG>
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32 * Fused multiply-add: Compute x * y + z with a single rounding error.
34 * A double has more than twice as much precision than a float, so
35 * direct double-precision arithmetic suffices, except where double
38 float fmaf(float x, float y, float z)
45 EXTRACT_WORDS(hr, lr, result);
46 /* Common case: The double precision result is fine. */
47 if ((lr & 0x1fffffff) != 0x10000000 || /* not a halfway case */
48 (hr & 0x7ff00000) == 0x7ff00000 || /* NaN */
49 result - xy == z || /* exact */
50 fegetround() != FE_TONEAREST) /* not round-to-nearest */
54 * If result is inexact, and exactly halfway between two float values,
55 * we need to adjust the low-order bit in the direction of the error.
58 fesetround(FE_TOWARDZERO);
60 volatile double vxy = xy; /* XXX work around gcc CSE bug */
61 double adjusted_result = vxy + z;
62 fesetround(FE_TONEAREST);
63 if (result == adjusted_result)
64 SET_LOW_WORD(adjusted_result, lr + 1);
65 return (adjusted_result);