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| </pre><pre class="rust"><code><span class="comment">/* origin: FreeBSD /usr/src/lib/msun/src/s_log1pf.c */</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">core::f32</span>; |
| |
| <span class="kw">const</span> <span class="ident">LN2_HI</span>: <span class="ident">f32</span> <span class="op">=</span> <span class="number">6.9313812256e-01</span>; <span class="comment">/* 0x3f317180 */</span> |
| <span class="kw">const</span> <span class="ident">LN2_LO</span>: <span class="ident">f32</span> <span class="op">=</span> <span class="number">9.0580006145e-06</span>; <span class="comment">/* 0x3717f7d1 */</span> |
| <span class="comment">/* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */</span> |
| <span class="kw">const</span> <span class="ident">LG1</span>: <span class="ident">f32</span> <span class="op">=</span> <span class="number">0.66666662693</span>; <span class="comment">/* 0xaaaaaa.0p-24 */</span> |
| <span class="kw">const</span> <span class="ident">LG2</span>: <span class="ident">f32</span> <span class="op">=</span> <span class="number">0.40000972152</span>; <span class="comment">/* 0xccce13.0p-25 */</span> |
| <span class="kw">const</span> <span class="ident">LG3</span>: <span class="ident">f32</span> <span class="op">=</span> <span class="number">0.28498786688</span>; <span class="comment">/* 0x91e9ee.0p-25 */</span> |
| <span class="kw">const</span> <span class="ident">LG4</span>: <span class="ident">f32</span> <span class="op">=</span> <span class="number">0.24279078841</span>; <span class="comment">/* 0xf89e26.0p-26 */</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">log1pf</span>(<span class="ident">x</span>: <span class="ident">f32</span>) -> <span class="ident">f32</span> { |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ui</span>: <span class="ident">u32</span> <span class="op">=</span> <span class="ident">x</span>.<span class="ident">to_bits</span>(); |
| <span class="kw">let</span> <span class="ident">hfsq</span>: <span class="ident">f32</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">f</span>: <span class="ident">f32</span> <span class="op">=</span> <span class="number">0.</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">c</span>: <span class="ident">f32</span> <span class="op">=</span> <span class="number">0.</span>; |
| <span class="kw">let</span> <span class="ident">s</span>: <span class="ident">f32</span>; |
| <span class="kw">let</span> <span class="ident">z</span>: <span class="ident">f32</span>; |
| <span class="kw">let</span> <span class="ident">r</span>: <span class="ident">f32</span>; |
| <span class="kw">let</span> <span class="ident">w</span>: <span class="ident">f32</span>; |
| <span class="kw">let</span> <span class="ident">t1</span>: <span class="ident">f32</span>; |
| <span class="kw">let</span> <span class="ident">t2</span>: <span class="ident">f32</span>; |
| <span class="kw">let</span> <span class="ident">dk</span>: <span class="ident">f32</span>; |
| <span class="kw">let</span> <span class="ident">ix</span>: <span class="ident">u32</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">iu</span>: <span class="ident">u32</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">k</span>: <span class="ident">i32</span>; |
| |
| <span class="ident">ix</span> <span class="op">=</span> <span class="ident">ui</span>; |
| <span class="ident">k</span> <span class="op">=</span> <span class="number">1</span>; |
| <span class="kw">if</span> <span class="ident">ix</span> <span class="op"><</span> <span class="number">0x3ed413d0</span> <span class="op">|</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="number">0</span> { |
| <span class="comment">/* 1+x < sqrt(2)+ */</span> |
| <span class="kw">if</span> <span class="ident">ix</span> <span class="op">></span><span class="op">=</span> <span class="number">0xbf800000</span> { |
| <span class="comment">/* x <= -1.0 */</span> |
| <span class="kw">if</span> <span class="ident">x</span> <span class="op">==</span> <span class="op">-</span><span class="number">1.</span> { |
| <span class="kw">return</span> <span class="ident">x</span> <span class="op">/</span> <span class="number">0.0</span>; <span class="comment">/* log1p(-1)=+inf */</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="number">0.0</span>; <span class="comment">/* log1p(x<-1)=NaN */</span> |
| } |
| <span class="kw">if</span> <span class="ident">ix</span> <span class="op"><</span><span class="op"><</span> <span class="number">1</span> <span class="op"><</span> <span class="number">0x33800000</span> <span class="op"><</span><span class="op"><</span> <span class="number">1</span> { |
| <span class="comment">/* |x| < 2**-24 */</span> |
| <span class="comment">/* underflow if subnormal */</span> |
| <span class="kw">if</span> (<span class="ident">ix</span> <span class="op">&</span> <span class="number">0x7f800000</span>) <span class="op">==</span> <span class="number">0</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="kw">if</span> <span class="ident">ix</span> <span class="op"><</span><span class="op">=</span> <span class="number">0xbe95f619</span> { |
| <span class="comment">/* sqrt(2)/2- <= 1+x < sqrt(2)+ */</span> |
| <span class="ident">k</span> <span class="op">=</span> <span class="number">0</span>; |
| <span class="ident">c</span> <span class="op">=</span> <span class="number">0.</span>; |
| <span class="ident">f</span> <span class="op">=</span> <span class="ident">x</span>; |
| } |
| } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">ix</span> <span class="op">></span><span class="op">=</span> <span class="number">0x7f800000</span> { |
| <span class="kw">return</span> <span class="ident">x</span>; |
| } |
| <span class="kw">if</span> <span class="ident">k</span> <span class="op">></span> <span class="number">0</span> { |
| <span class="ident">ui</span> <span class="op">=</span> (<span class="number">1.</span> <span class="op">+</span> <span class="ident">x</span>).<span class="ident">to_bits</span>(); |
| <span class="ident">iu</span> <span class="op">=</span> <span class="ident">ui</span>; |
| <span class="ident">iu</span> <span class="op">+</span><span class="op">=</span> <span class="number">0x3f800000</span> <span class="op">-</span> <span class="number">0x3f3504f3</span>; |
| <span class="ident">k</span> <span class="op">=</span> (<span class="ident">iu</span> <span class="op">></span><span class="op">></span> <span class="number">23</span>) <span class="kw">as</span> <span class="ident">i32</span> <span class="op">-</span> <span class="number">0x7f</span>; |
| <span class="comment">/* correction term ~ log(1+x)-log(u), avoid underflow in c/u */</span> |
| <span class="kw">if</span> <span class="ident">k</span> <span class="op"><</span> <span class="number">25</span> { |
| <span class="ident">c</span> <span class="op">=</span> <span class="kw">if</span> <span class="ident">k</span> <span class="op">></span><span class="op">=</span> <span class="number">2</span> { |
| <span class="number">1.</span> <span class="op">-</span> (<span class="ident">f32::from_bits</span>(<span class="ident">ui</span>) <span class="op">-</span> <span class="ident">x</span>) |
| } <span class="kw">else</span> { |
| <span class="ident">x</span> <span class="op">-</span> (<span class="ident">f32::from_bits</span>(<span class="ident">ui</span>) <span class="op">-</span> <span class="number">1.</span>) |
| }; |
| <span class="ident">c</span> <span class="op">/</span><span class="op">=</span> <span class="ident">f32::from_bits</span>(<span class="ident">ui</span>); |
| } <span class="kw">else</span> { |
| <span class="ident">c</span> <span class="op">=</span> <span class="number">0.</span>; |
| } |
| <span class="comment">/* reduce u into [sqrt(2)/2, sqrt(2)] */</span> |
| <span class="ident">iu</span> <span class="op">=</span> (<span class="ident">iu</span> <span class="op">&</span> <span class="number">0x007fffff</span>) <span class="op">+</span> <span class="number">0x3f3504f3</span>; |
| <span class="ident">ui</span> <span class="op">=</span> <span class="ident">iu</span>; |
| <span class="ident">f</span> <span class="op">=</span> <span class="ident">f32::from_bits</span>(<span class="ident">ui</span>) <span class="op">-</span> <span class="number">1.</span>; |
| } |
| <span class="ident">s</span> <span class="op">=</span> <span class="ident">f</span> <span class="op">/</span> (<span class="number">2.0</span> <span class="op">+</span> <span class="ident">f</span>); |
| <span class="ident">z</span> <span class="op">=</span> <span class="ident">s</span> <span class="op">*</span> <span class="ident">s</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="ident">t1</span> <span class="op">=</span> <span class="ident">w</span> <span class="op">*</span> (<span class="ident">LG2</span> <span class="op">+</span> <span class="ident">w</span> <span class="op">*</span> <span class="ident">LG4</span>); |
| <span class="ident">t2</span> <span class="op">=</span> <span class="ident">z</span> <span class="op">*</span> (<span class="ident">LG1</span> <span class="op">+</span> <span class="ident">w</span> <span class="op">*</span> <span class="ident">LG3</span>); |
| <span class="ident">r</span> <span class="op">=</span> <span class="ident">t2</span> <span class="op">+</span> <span class="ident">t1</span>; |
| <span class="ident">hfsq</span> <span class="op">=</span> <span class="number">0.5</span> <span class="op">*</span> <span class="ident">f</span> <span class="op">*</span> <span class="ident">f</span>; |
| <span class="ident">dk</span> <span class="op">=</span> <span class="ident">k</span> <span class="kw">as</span> <span class="ident">f32</span>; |
| <span class="ident">s</span> <span class="op">*</span> (<span class="ident">hfsq</span> <span class="op">+</span> <span class="ident">r</span>) <span class="op">+</span> (<span class="ident">dk</span> <span class="op">*</span> <span class="ident">LN2_LO</span> <span class="op">+</span> <span class="ident">c</span>) <span class="op">-</span> <span class="ident">hfsq</span> <span class="op">+</span> <span class="ident">f</span> <span class="op">+</span> <span class="ident">dk</span> <span class="op">*</span> <span class="ident">LN2_HI</span> |
| } |
| </code></pre></div> |
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