| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/libm-0.2.7/src/math/fmaf.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>fmaf.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="../../../source-script.js"></script><script defer src="../../../source-files.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../libm/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../libm/index.html"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="comment">/* 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. |
| */ |
| |
| </span><span class="kw">use </span>core::f32; |
| <span class="kw">use </span>core::ptr::read_volatile; |
| |
| <span class="kw">use </span><span class="kw">super</span>::fenv::{ |
| feclearexcept, fegetround, feraiseexcept, fetestexcept, FE_INEXACT, FE_TONEAREST, FE_UNDERFLOW, |
| }; |
| |
| <span class="comment">/* |
| * 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. |
| */ |
| |
| </span><span class="doccomment">/// Floating multiply add (f32) |
| /// |
| /// Computes `(x*y)+z`, rounded as one ternary operation: |
| /// Computes the value (as if) to infinite precision and rounds once to the result format, |
| /// according to the rounding mode characterized by the value of FLT_ROUNDS. |
| </span><span class="attribute">#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] |
| </span><span class="kw">pub fn </span>fmaf(x: f32, y: f32, <span class="kw-2">mut </span>z: f32) -> f32 { |
| <span class="kw">let </span>xy: f64; |
| <span class="kw">let </span><span class="kw-2">mut </span>result: f64; |
| <span class="kw">let </span><span class="kw-2">mut </span>ui: u64; |
| <span class="kw">let </span>e: i32; |
| |
| xy = x <span class="kw">as </span>f64 * y <span class="kw">as </span>f64; |
| result = xy + z <span class="kw">as </span>f64; |
| ui = result.to_bits(); |
| e = (ui >> <span class="number">52</span>) <span class="kw">as </span>i32 & <span class="number">0x7ff</span>; |
| <span class="comment">/* Common case: The double precision result is fine. */ |
| </span><span class="kw">if </span>( |
| <span class="comment">/* not a halfway case */ |
| </span>ui & <span class="number">0x1fffffff</span>) != <span class="number">0x10000000 </span>|| |
| <span class="comment">/* NaN */ |
| </span>e == <span class="number">0x7ff </span>|| |
| <span class="comment">/* exact */ |
| </span>(result - xy == z <span class="kw">as </span>f64 && result - z <span class="kw">as </span>f64 == xy) || |
| <span class="comment">/* not round-to-nearest */ |
| </span>fegetround() != FE_TONEAREST |
| { |
| <span class="comment">/* |
| underflow may not be raised correctly, example: |
| fmaf(0x1p-120f, 0x1p-120f, 0x1p-149f) |
| */ |
| </span><span class="kw">if </span>e < <span class="number">0x3ff </span>- <span class="number">126 </span>&& e >= <span class="number">0x3ff </span>- <span class="number">149 </span>&& fetestexcept(FE_INEXACT) != <span class="number">0 </span>{ |
| feclearexcept(FE_INEXACT); |
| <span class="comment">// prevent `xy + vz` from being CSE'd with `xy + z` above |
| </span><span class="kw">let </span>vz: f32 = <span class="kw">unsafe </span>{ read_volatile(<span class="kw-2">&</span>z) }; |
| result = xy + vz <span class="kw">as </span>f64; |
| <span class="kw">if </span>fetestexcept(FE_INEXACT) != <span class="number">0 </span>{ |
| feraiseexcept(FE_UNDERFLOW); |
| } <span class="kw">else </span>{ |
| feraiseexcept(FE_INEXACT); |
| } |
| } |
| z = result <span class="kw">as </span>f32; |
| <span class="kw">return </span>z; |
| } |
| |
| <span class="comment">/* |
| * 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. |
| */ |
| </span><span class="kw">let </span>neg = ui >> <span class="number">63 </span>!= <span class="number">0</span>; |
| <span class="kw">let </span>err = <span class="kw">if </span>neg == (z <span class="kw">as </span>f64 > xy) { |
| xy - result + z <span class="kw">as </span>f64 |
| } <span class="kw">else </span>{ |
| z <span class="kw">as </span>f64 - result + xy |
| }; |
| <span class="kw">if </span>neg == (err < <span class="number">0.0</span>) { |
| ui += <span class="number">1</span>; |
| } <span class="kw">else </span>{ |
| ui -= <span class="number">1</span>; |
| } |
| f64::from_bits(ui) <span class="kw">as </span>f32 |
| } |
| |
| <span class="attribute">#[cfg(test)] |
| </span><span class="kw">mod </span>tests { |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>issue_263() { |
| <span class="kw">let </span>a = f32::from_bits(<span class="number">1266679807</span>); |
| <span class="kw">let </span>b = f32::from_bits(<span class="number">1300234242</span>); |
| <span class="kw">let </span>c = f32::from_bits(<span class="number">1115553792</span>); |
| <span class="kw">let </span>expected = f32::from_bits(<span class="number">1501560833</span>); |
| <span class="macro">assert_eq!</span>(<span class="kw">super</span>::fmaf(a, b, c), expected); |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="libm" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
