diff options
Diffstat (limited to 'lib/mlibc/options/ansi/musl-generic-math/fmaf.c')
| -rw-r--r-- | lib/mlibc/options/ansi/musl-generic-math/fmaf.c | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/lib/mlibc/options/ansi/musl-generic-math/fmaf.c b/lib/mlibc/options/ansi/musl-generic-math/fmaf.c new file mode 100644 index 0000000..aa57feb --- /dev/null +++ b/lib/mlibc/options/ansi/musl-generic-math/fmaf.c @@ -0,0 +1,93 @@ +/* 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 <math.h> +#include <stdint.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) +{ + #pragma STDC FENV_ACCESS ON + double xy, result; + union {double f; uint64_t i;} u; + int e; + + xy = (double)x * y; + result = xy + z; + u.f = result; + e = u.i>>52 & 0x7ff; + /* Common case: The double precision result is fine. */ + if ((u.i & 0x1fffffff) != 0x10000000 || /* not a halfway case */ + e == 0x7ff || /* NaN */ + result - xy == z || /* exact */ + fegetround() != FE_TONEAREST) /* not round-to-nearest */ + { + /* + underflow may not be raised correctly, example: + fmaf(0x1p-120f, 0x1p-120f, 0x1p-149f) + */ +#if defined(FE_INEXACT) && defined(FE_UNDERFLOW) + if (e < 0x3ff-126 && e >= 0x3ff-149 && fetestexcept(FE_INEXACT)) { + feclearexcept(FE_INEXACT); + /* TODO: gcc and clang bug workaround */ + volatile float vz = z; + result = xy + vz; + if (fetestexcept(FE_INEXACT)) + feraiseexcept(FE_UNDERFLOW); + else + feraiseexcept(FE_INEXACT); + } +#endif + z = result; + return z; + } + + /* + * 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) { + u.f = adjusted_result; + u.i++; + adjusted_result = u.f; + } + z = adjusted_result; + return z; +} |