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| </pre><pre class="rust"><code><span class="comment">/* origin: FreeBSD /usr/src/lib/msun/src/s_atanf.c */</span> |
| <span class="comment">/* |
| * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. |
| */</span> |
| <span class="comment">/* |
| * ==================================================== |
| * 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. |
| * ==================================================== |
| */</span> |
| |
| <span class="kw">use</span> <span class="ident"><span class="kw">super</span>::fabsf</span>; |
| |
| <span class="kw">const</span> <span class="ident">ATAN_HI</span>: [<span class="ident">f32</span>; <span class="number">4</span>] <span class="op">=</span> [ |
| <span class="number">4.6364760399e-01</span>, <span class="comment">/* atan(0.5)hi 0x3eed6338 */</span> |
| <span class="number">7.8539812565e-01</span>, <span class="comment">/* atan(1.0)hi 0x3f490fda */</span> |
| <span class="number">9.8279368877e-01</span>, <span class="comment">/* atan(1.5)hi 0x3f7b985e */</span> |
| <span class="number">1.5707962513e+00</span>, <span class="comment">/* atan(inf)hi 0x3fc90fda */</span> |
| ]; |
| |
| <span class="kw">const</span> <span class="ident">ATAN_LO</span>: [<span class="ident">f32</span>; <span class="number">4</span>] <span class="op">=</span> [ |
| <span class="number">5.0121582440e-09</span>, <span class="comment">/* atan(0.5)lo 0x31ac3769 */</span> |
| <span class="number">3.7748947079e-08</span>, <span class="comment">/* atan(1.0)lo 0x33222168 */</span> |
| <span class="number">3.4473217170e-08</span>, <span class="comment">/* atan(1.5)lo 0x33140fb4 */</span> |
| <span class="number">7.5497894159e-08</span>, <span class="comment">/* atan(inf)lo 0x33a22168 */</span> |
| ]; |
| |
| <span class="kw">const</span> <span class="ident">A_T</span>: [<span class="ident">f32</span>; <span class="number">5</span>] <span class="op">=</span> [ |
| <span class="number">3.3333328366e-01</span>, |
| <span class="op">-</span><span class="number">1.9999158382e-01</span>, |
| <span class="number">1.4253635705e-01</span>, |
| <span class="op">-</span><span class="number">1.0648017377e-01</span>, |
| <span class="number">6.1687607318e-02</span>, |
| ]; |
| |
| <span class="doccomment">/// Arctangent (f32)</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// Computes the inverse tangent (arc tangent) of the input value.</span> |
| <span class="doccomment">/// Returns a value in radians, in the range of -pi/2 to pi/2.</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::no_panic</span>)]</span> |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">atanf</span>(<span class="kw-2">mut</span> <span class="ident">x</span>: <span class="ident">f32</span>) -> <span class="ident">f32</span> { |
| <span class="kw">let</span> <span class="ident">x1p_120</span> <span class="op">=</span> <span class="ident">f32::from_bits</span>(<span class="number">0x03800000</span>); <span class="comment">// 0x1p-120 === 2 ^ (-120)</span> |
| |
| <span class="kw">let</span> <span class="ident">z</span>: <span class="ident">f32</span>; |
| |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ix</span> <span class="op">=</span> <span class="ident">x</span>.<span class="ident">to_bits</span>(); |
| <span class="kw">let</span> <span class="ident">sign</span> <span class="op">=</span> (<span class="ident">ix</span> <span class="op">></span><span class="op">></span> <span class="number">31</span>) <span class="op">!</span><span class="op">=</span> <span class="number">0</span>; |
| <span class="ident">ix</span> <span class="op">&=</span> <span class="number">0x7fffffff</span>; |
| |
| <span class="kw">if</span> <span class="ident">ix</span> <span class="op">></span><span class="op">=</span> <span class="number">0x4c800000</span> { |
| <span class="comment">/* if |x| >= 2**26 */</span> |
| <span class="kw">if</span> <span class="ident">x</span>.<span class="ident">is_nan</span>() { |
| <span class="kw">return</span> <span class="ident">x</span>; |
| } |
| <span class="ident">z</span> <span class="op">=</span> <span class="ident">ATAN_HI</span>[<span class="number">3</span>] <span class="op">+</span> <span class="ident">x1p_120</span>; |
| <span class="kw">return</span> <span class="kw">if</span> <span class="ident">sign</span> { <span class="op">-</span><span class="ident">z</span> } <span class="kw">else</span> { <span class="ident">z</span> }; |
| } |
| <span class="kw">let</span> <span class="ident">id</span> <span class="op">=</span> <span class="kw">if</span> <span class="ident">ix</span> <span class="op"><</span> <span class="number">0x3ee00000</span> { |
| <span class="comment">/* |x| < 0.4375 */</span> |
| <span class="kw">if</span> <span class="ident">ix</span> <span class="op"><</span> <span class="number">0x39800000</span> { |
| <span class="comment">/* |x| < 2**-12 */</span> |
| <span class="kw">if</span> <span class="ident">ix</span> <span class="op"><</span> <span class="number">0x00800000</span> { |
| <span class="comment">/* raise underflow for subnormal x */</span> |
| <span class="macro">force_eval!</span>(<span class="ident">x</span> <span class="op">*</span> <span class="ident">x</span>); |
| } |
| <span class="kw">return</span> <span class="ident">x</span>; |
| } |
| <span class="op">-</span><span class="number">1</span> |
| } <span class="kw">else</span> { |
| <span class="ident">x</span> <span class="op">=</span> <span class="ident">fabsf</span>(<span class="ident">x</span>); |
| <span class="kw">if</span> <span class="ident">ix</span> <span class="op"><</span> <span class="number">0x3f980000</span> { |
| <span class="comment">/* |x| < 1.1875 */</span> |
| <span class="kw">if</span> <span class="ident">ix</span> <span class="op"><</span> <span class="number">0x3f300000</span> { |
| <span class="comment">/* 7/16 <= |x| < 11/16 */</span> |
| <span class="ident">x</span> <span class="op">=</span> (<span class="number">2.</span> <span class="op">*</span> <span class="ident">x</span> <span class="op">-</span> <span class="number">1.</span>) <span class="op">/</span> (<span class="number">2.</span> <span class="op">+</span> <span class="ident">x</span>); |
| <span class="number">0</span> |
| } <span class="kw">else</span> { |
| <span class="comment">/* 11/16 <= |x| < 19/16 */</span> |
| <span class="ident">x</span> <span class="op">=</span> (<span class="ident">x</span> <span class="op">-</span> <span class="number">1.</span>) <span class="op">/</span> (<span class="ident">x</span> <span class="op">+</span> <span class="number">1.</span>); |
| <span class="number">1</span> |
| } |
| } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">ix</span> <span class="op"><</span> <span class="number">0x401c0000</span> { |
| <span class="comment">/* |x| < 2.4375 */</span> |
| <span class="ident">x</span> <span class="op">=</span> (<span class="ident">x</span> <span class="op">-</span> <span class="number">1.5</span>) <span class="op">/</span> (<span class="number">1.</span> <span class="op">+</span> <span class="number">1.5</span> <span class="op">*</span> <span class="ident">x</span>); |
| <span class="number">2</span> |
| } <span class="kw">else</span> { |
| <span class="comment">/* 2.4375 <= |x| < 2**26 */</span> |
| <span class="ident">x</span> <span class="op">=</span> <span class="op">-</span><span class="number">1.</span> <span class="op">/</span> <span class="ident">x</span>; |
| <span class="number">3</span> |
| } |
| }; |
| <span class="comment">/* end of argument reduction */</span> |
| <span class="ident">z</span> <span class="op">=</span> <span class="ident">x</span> <span class="op">*</span> <span class="ident">x</span>; |
| <span class="kw">let</span> <span class="ident">w</span> <span class="op">=</span> <span class="ident">z</span> <span class="op">*</span> <span class="ident">z</span>; |
| <span class="comment">/* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */</span> |
| <span class="kw">let</span> <span class="ident">s1</span> <span class="op">=</span> <span class="ident">z</span> <span class="op">*</span> (<span class="ident">A_T</span>[<span class="number">0</span>] <span class="op">+</span> <span class="ident">w</span> <span class="op">*</span> (<span class="ident">A_T</span>[<span class="number">2</span>] <span class="op">+</span> <span class="ident">w</span> <span class="op">*</span> <span class="ident">A_T</span>[<span class="number">4</span>])); |
| <span class="kw">let</span> <span class="ident">s2</span> <span class="op">=</span> <span class="ident">w</span> <span class="op">*</span> (<span class="ident">A_T</span>[<span class="number">1</span>] <span class="op">+</span> <span class="ident">w</span> <span class="op">*</span> <span class="ident">A_T</span>[<span class="number">3</span>]); |
| <span class="kw">if</span> <span class="ident">id</span> <span class="op"><</span> <span class="number">0</span> { |
| <span class="kw">return</span> <span class="ident">x</span> <span class="op">-</span> <span class="ident">x</span> <span class="op">*</span> (<span class="ident">s1</span> <span class="op">+</span> <span class="ident">s2</span>); |
| } |
| <span class="kw">let</span> <span class="ident">id</span> <span class="op">=</span> <span class="ident">id</span> <span class="kw">as</span> <span class="ident">usize</span>; |
| <span class="kw">let</span> <span class="ident">z</span> <span class="op">=</span> <span class="ident">ATAN_HI</span>[<span class="ident">id</span>] <span class="op">-</span> ((<span class="ident">x</span> <span class="op">*</span> (<span class="ident">s1</span> <span class="op">+</span> <span class="ident">s2</span>) <span class="op">-</span> <span class="ident">ATAN_LO</span>[<span class="ident">id</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">z</span> |
| } <span class="kw">else</span> { |
| <span class="ident">z</span> |
| } |
| } |
| </code></pre></div> |
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