<!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 to the Rust file `/home/mrh/.cargo/registry/src/github.com-1ecc6299db9ec823/libm-0.1.4/src/math/tanh.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>tanh.rs.html -- source</title><link rel="stylesheet" type="text/css" href="../../../normalize.css"><link rel="stylesheet" type="text/css" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../../dark.css"><link rel="stylesheet" type="text/css" href="../../../light.css" id="themeStyle"><script src="../../../storage.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="shortcut icon" href="../../../favicon.ico"><style type="text/css">#crate-search{background-image:url("../../../down-arrow.svg");}</style></head><body class="rustdoc source"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../../libm/index.html'><div class='logo-container'><img src='../../../rust-logo.png' alt='logo'></div></a></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../../../settings.html"><img src="../../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1"> 1</span>
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</pre><div class="example-wrap"><pre class="rust ">
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">expm1</span>;
<span class="comment">/* tanh(x) = (exp(x) - exp(-x))/(exp(x) + exp(-x))
* = (exp(2*x) - 1)/(exp(2*x) - 1 + 2)
* = (1 - exp(-2*x))/(exp(-2*x) - 1 + 2)
*/</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="attribute">#[<span class="ident">cfg_attr</span>(<span class="ident">all</span>(<span class="ident">test</span>, <span class="ident">assert_no_panic</span>), <span class="ident">no_panic</span>::<span class="ident">no_panic</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">tanh</span>(<span class="kw-2">mut</span> <span class="ident">x</span>: <span class="ident">f64</span>) <span class="op">-</span><span class="op">></span> <span class="ident">f64</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">uf</span>: <span class="ident">f64</span> <span class="op">=</span> <span class="ident">x</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ui</span>: <span class="ident">u64</span> <span class="op">=</span> <span class="ident">f64</span>::<span class="ident">to_bits</span>(<span class="ident">uf</span>);
<span class="kw">let</span> <span class="ident">w</span>: <span class="ident">u32</span>;
<span class="kw">let</span> <span class="ident">sign</span>: <span class="ident">bool</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">t</span>: <span class="ident">f64</span>;
<span class="comment">/* x = |x| */</span>
<span class="ident">sign</span> <span class="op">=</span> <span class="ident">ui</span> <span class="op">></span><span class="op">></span> <span class="number">63</span> <span class="op">!</span><span class="op">=</span> <span class="number">0</span>;
<span class="ident">ui</span> <span class="kw-2">&</span><span class="op">=</span> <span class="op">!</span><span class="number">1</span> <span class="op">/</span> <span class="number">2</span>;
<span class="ident">uf</span> <span class="op">=</span> <span class="ident">f64</span>::<span class="ident">from_bits</span>(<span class="ident">ui</span>);
<span class="ident">x</span> <span class="op">=</span> <span class="ident">uf</span>;
<span class="ident">w</span> <span class="op">=</span> (<span class="ident">ui</span> <span class="op">></span><span class="op">></span> <span class="number">32</span>) <span class="kw">as</span> <span class="ident">u32</span>;
<span class="kw">if</span> <span class="ident">w</span> <span class="op">></span> <span class="number">0x3fe193ea</span> {
<span class="comment">/* |x| > log(3)/2 ~= 0.5493 or nan */</span>
<span class="kw">if</span> <span class="ident">w</span> <span class="op">></span> <span class="number">0x40340000</span> {
<span class="comment">/* |x| > 20 or nan */</span>
<span class="comment">/* note: this branch avoids raising overflow */</span>
<span class="ident">t</span> <span class="op">=</span> <span class="number">1.0</span> <span class="op">-</span> <span class="number">0.0</span> <span class="op">/</span> <span class="ident">x</span>;
} <span class="kw">else</span> {
<span class="ident">t</span> <span class="op">=</span> <span class="ident">expm1</span>(<span class="number">2.0</span> <span class="op">*</span> <span class="ident">x</span>);
<span class="ident">t</span> <span class="op">=</span> <span class="number">1.0</span> <span class="op">-</span> <span class="number">2.0</span> <span class="op">/</span> (<span class="ident">t</span> <span class="op">+</span> <span class="number">2.0</span>);
}
} <span class="kw">else</span> <span class="kw">if</span> <span class="ident">w</span> <span class="op">></span> <span class="number">0x3fd058ae</span> {
<span class="comment">/* |x| > log(5/3)/2 ~= 0.2554 */</span>
<span class="ident">t</span> <span class="op">=</span> <span class="ident">expm1</span>(<span class="number">2.0</span> <span class="op">*</span> <span class="ident">x</span>);
<span class="ident">t</span> <span class="op">=</span> <span class="ident">t</span> <span class="op">/</span> (<span class="ident">t</span> <span class="op">+</span> <span class="number">2.0</span>);
} <span class="kw">else</span> <span class="kw">if</span> <span class="ident">w</span> <span class="op">></span><span class="op">=</span> <span class="number">0x00100000</span> {
<span class="comment">/* |x| >= 0x1p-1022, up to 2ulp error in [0.1,0.2554] */</span>
<span class="ident">t</span> <span class="op">=</span> <span class="ident">expm1</span>(<span class="op">-</span><span class="number">2.0</span> <span class="op">*</span> <span class="ident">x</span>);
<span class="ident">t</span> <span class="op">=</span> <span class="op">-</span><span class="ident">t</span> <span class="op">/</span> (<span class="ident">t</span> <span class="op">+</span> <span class="number">2.0</span>);
} <span class="kw">else</span> {
<span class="comment">/* |x| is subnormal */</span>
<span class="comment">/* note: the branch above would not raise underflow in [0x1p-1023,0x1p-1022) */</span>
<span class="macro">force_eval</span><span class="macro">!</span>(<span class="ident">x</span> <span class="kw">as</span> <span class="ident">f32</span>);
<span class="ident">t</span> <span class="op">=</span> <span class="ident">x</span>;
}
<span class="kw">if</span> <span class="ident">sign</span> {
<span class="op">-</span><span class="ident">t</span>
} <span class="kw">else</span> {
<span class="ident">t</span>
}
}
</pre></div>
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