| <!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/cbrtf.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>cbrtf.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_cbrtf.c */ |
| /* |
| * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. |
| * Debugged and optimized by Bruce D. Evans. |
| */ |
| /* |
| * ==================================================== |
| * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| * |
| * Developed at SunPro, a Sun Microsystems, Inc. business. |
| * Permission to use, copy, modify, and distribute this |
| * software is freely granted, provided that this notice |
| * is preserved. |
| * ==================================================== |
| */ |
| /* cbrtf(x) |
| * Return cube root of x |
| */ |
| |
| </span><span class="kw">use </span>core::f32; |
| |
| <span class="kw">const </span>B1: u32 = <span class="number">709958130</span>; <span class="comment">/* B1 = (127-127.0/3-0.03306235651)*2**23 */ |
| </span><span class="kw">const </span>B2: u32 = <span class="number">642849266</span>; <span class="comment">/* B2 = (127-127.0/3-24/3-0.03306235651)*2**23 */ |
| |
| </span><span class="doccomment">/// Cube root (f32) |
| /// |
| /// Computes the cube root of the argument. |
| </span><span class="attribute">#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] |
| </span><span class="kw">pub fn </span>cbrtf(x: f32) -> f32 { |
| <span class="kw">let </span>x1p24 = f32::from_bits(<span class="number">0x4b800000</span>); <span class="comment">// 0x1p24f === 2 ^ 24 |
| |
| </span><span class="kw">let </span><span class="kw-2">mut </span>r: f64; |
| <span class="kw">let </span><span class="kw-2">mut </span>t: f64; |
| <span class="kw">let </span><span class="kw-2">mut </span>ui: u32 = x.to_bits(); |
| <span class="kw">let </span><span class="kw-2">mut </span>hx: u32 = ui & <span class="number">0x7fffffff</span>; |
| |
| <span class="kw">if </span>hx >= <span class="number">0x7f800000 </span>{ |
| <span class="comment">/* cbrt(NaN,INF) is itself */ |
| </span><span class="kw">return </span>x + x; |
| } |
| |
| <span class="comment">/* rough cbrt to 5 bits */ |
| </span><span class="kw">if </span>hx < <span class="number">0x00800000 </span>{ |
| <span class="comment">/* zero or subnormal? */ |
| </span><span class="kw">if </span>hx == <span class="number">0 </span>{ |
| <span class="kw">return </span>x; <span class="comment">/* cbrt(+-0) is itself */ |
| </span>} |
| ui = (x * x1p24).to_bits(); |
| hx = ui & <span class="number">0x7fffffff</span>; |
| hx = hx / <span class="number">3 </span>+ B2; |
| } <span class="kw">else </span>{ |
| hx = hx / <span class="number">3 </span>+ B1; |
| } |
| ui &= <span class="number">0x80000000</span>; |
| ui |= hx; |
| |
| <span class="comment">/* |
| * First step Newton iteration (solving t*t-x/t == 0) to 16 bits. In |
| * double precision so that its terms can be arranged for efficiency |
| * without causing overflow or underflow. |
| */ |
| </span>t = f32::from_bits(ui) <span class="kw">as </span>f64; |
| r = t * t * t; |
| t = t * (x <span class="kw">as </span>f64 + x <span class="kw">as </span>f64 + r) / (x <span class="kw">as </span>f64 + r + r); |
| |
| <span class="comment">/* |
| * Second step Newton iteration to 47 bits. In double precision for |
| * efficiency and accuracy. |
| */ |
| </span>r = t * t * t; |
| t = t * (x <span class="kw">as </span>f64 + x <span class="kw">as </span>f64 + r) / (x <span class="kw">as </span>f64 + r + r); |
| |
| <span class="comment">/* rounding to 24 bits is perfect in round-to-nearest mode */ |
| </span>t <span class="kw">as </span>f32 |
| } |
| </code></pre></div> |
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