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<span class="comment">// Copyright 2015 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span>
<span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>
<span class="doccomment">//! Decodes a floating-point value into individual parts and error ranges.</span>
<span class="kw">use</span> {<span class="ident">f32</span>, <span class="ident">f64</span>};
<span class="kw">use</span> <span class="ident">num</span>::<span class="ident">FpCategory</span>;
<span class="kw">use</span> <span class="ident">num</span>::<span class="ident">dec2flt</span>::<span class="ident">rawfp</span>::<span class="ident">RawFloat</span>;
<span class="doccomment">/// Decoded unsigned finite value, such that:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// - The original value equals to `mant * 2^exp`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// - Any number from `(mant - minus) * 2^exp` to `(mant + plus) * 2^exp` will</span>
<span class="doccomment">/// round to the original value. The range is inclusive only when</span>
<span class="doccomment">/// `inclusive` is true.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Decoded</span> {
<span class="doccomment">/// The scaled mantissa.</span>
<span class="kw">pub</span> <span class="ident">mant</span>: <span class="ident">u64</span>,
<span class="doccomment">/// The lower error range.</span>
<span class="kw">pub</span> <span class="ident">minus</span>: <span class="ident">u64</span>,
<span class="doccomment">/// The upper error range.</span>
<span class="kw">pub</span> <span class="ident">plus</span>: <span class="ident">u64</span>,
<span class="doccomment">/// The shared exponent in base 2.</span>
<span class="kw">pub</span> <span class="ident">exp</span>: <span class="ident">i16</span>,
<span class="doccomment">/// True when the error range is inclusive.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In IEEE 754, this is true when the original mantissa was even.</span>
<span class="kw">pub</span> <span class="ident">inclusive</span>: <span class="ident">bool</span>,
}
<span class="doccomment">/// Decoded unsigned value.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">FullDecoded</span> {
<span class="doccomment">/// Not-a-number.</span>
<span class="ident">Nan</span>,
<span class="doccomment">/// Infinities, either positive or negative.</span>
<span class="ident">Infinite</span>,
<span class="doccomment">/// Zero, either positive or negative.</span>
<span class="ident">Zero</span>,
<span class="doccomment">/// Finite numbers with further decoded fields.</span>
<span class="ident">Finite</span>(<span class="ident">Decoded</span>),
}
<span class="doccomment">/// A floating point type which can be `decode`d.</span>
<span class="kw">pub</span> <span class="kw">trait</span> <span class="ident">DecodableFloat</span>: <span class="ident">RawFloat</span> <span class="op">+</span> <span class="ident">Copy</span> {
<span class="doccomment">/// The minimum positive normalized value.</span>
<span class="kw">fn</span> <span class="ident">min_pos_norm_value</span>() <span class="op">-></span> <span class="self">Self</span>;
}
<span class="kw">impl</span> <span class="ident">DecodableFloat</span> <span class="kw">for</span> <span class="ident">f32</span> {
<span class="kw">fn</span> <span class="ident">min_pos_norm_value</span>() <span class="op">-></span> <span class="self">Self</span> { <span class="ident">f32</span>::<span class="ident">MIN_POSITIVE</span> }
}
<span class="kw">impl</span> <span class="ident">DecodableFloat</span> <span class="kw">for</span> <span class="ident">f64</span> {
<span class="kw">fn</span> <span class="ident">min_pos_norm_value</span>() <span class="op">-></span> <span class="self">Self</span> { <span class="ident">f64</span>::<span class="ident">MIN_POSITIVE</span> }
}
<span class="doccomment">/// Returns a sign (true when negative) and `FullDecoded` value</span>
<span class="doccomment">/// from given floating point number.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">decode</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">DecodableFloat</span><span class="op">></span>(<span class="ident">v</span>: <span class="ident">T</span>) <span class="op">-></span> (<span class="comment">/*negative?*/</span> <span class="ident">bool</span>, <span class="ident">FullDecoded</span>) {
<span class="kw">let</span> (<span class="ident">mant</span>, <span class="ident">exp</span>, <span class="ident">sign</span>) <span class="op">=</span> <span class="ident">v</span>.<span class="ident">integer_decode</span>();
<span class="kw">let</span> <span class="ident">even</span> <span class="op">=</span> (<span class="ident">mant</span> <span class="op">&</span> <span class="number">1</span>) <span class="op">==</span> <span class="number">0</span>;
<span class="kw">let</span> <span class="ident">decoded</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">v</span>.<span class="ident">classify</span>() {
<span class="ident">FpCategory</span>::<span class="ident">Nan</span> <span class="op">=></span> <span class="ident">FullDecoded</span>::<span class="ident">Nan</span>,
<span class="ident">FpCategory</span>::<span class="ident">Infinite</span> <span class="op">=></span> <span class="ident">FullDecoded</span>::<span class="ident">Infinite</span>,
<span class="ident">FpCategory</span>::<span class="ident">Zero</span> <span class="op">=></span> <span class="ident">FullDecoded</span>::<span class="ident">Zero</span>,
<span class="ident">FpCategory</span>::<span class="ident">Subnormal</span> <span class="op">=></span> {
<span class="comment">// neighbors: (mant - 2, exp) -- (mant, exp) -- (mant + 2, exp)</span>
<span class="comment">// Float::integer_decode always preserves the exponent,</span>
<span class="comment">// so the mantissa is scaled for subnormals.</span>
<span class="ident">FullDecoded</span>::<span class="ident">Finite</span>(<span class="ident">Decoded</span> { <span class="ident">mant</span>: <span class="ident">mant</span>, <span class="ident">minus</span>: <span class="number">1</span>, <span class="ident">plus</span>: <span class="number">1</span>,
<span class="ident">exp</span>: <span class="ident">exp</span>, <span class="ident">inclusive</span>: <span class="ident">even</span> })
}
<span class="ident">FpCategory</span>::<span class="ident">Normal</span> <span class="op">=></span> {
<span class="kw">let</span> <span class="ident">minnorm</span> <span class="op">=</span> <span class="op"><</span><span class="ident">T</span> <span class="kw">as</span> <span class="ident">DecodableFloat</span><span class="op">></span>::<span class="ident">min_pos_norm_value</span>().<span class="ident">integer_decode</span>();
<span class="kw">if</span> <span class="ident">mant</span> <span class="op">==</span> <span class="ident">minnorm</span>.<span class="number">0</span> {
<span class="comment">// neighbors: (maxmant, exp - 1) -- (minnormmant, exp) -- (minnormmant + 1, exp)</span>
<span class="comment">// where maxmant = minnormmant * 2 - 1</span>
<span class="ident">FullDecoded</span>::<span class="ident">Finite</span>(<span class="ident">Decoded</span> { <span class="ident">mant</span>: <span class="ident">mant</span> <span class="op"><<</span> <span class="number">2</span>, <span class="ident">minus</span>: <span class="number">1</span>, <span class="ident">plus</span>: <span class="number">2</span>,
<span class="ident">exp</span>: <span class="ident">exp</span> <span class="op">-</span> <span class="number">2</span>, <span class="ident">inclusive</span>: <span class="ident">even</span> })
} <span class="kw">else</span> {
<span class="comment">// neighbors: (mant - 1, exp) -- (mant, exp) -- (mant + 1, exp)</span>
<span class="ident">FullDecoded</span>::<span class="ident">Finite</span>(<span class="ident">Decoded</span> { <span class="ident">mant</span>: <span class="ident">mant</span> <span class="op"><<</span> <span class="number">1</span>, <span class="ident">minus</span>: <span class="number">1</span>, <span class="ident">plus</span>: <span class="number">1</span>,
<span class="ident">exp</span>: <span class="ident">exp</span> <span class="op">-</span> <span class="number">1</span>, <span class="ident">inclusive</span>: <span class="ident">even</span> })
}
}
};
(<span class="ident">sign</span> <span class="op"><</span> <span class="number">0</span>, <span class="ident">decoded</span>)
}
</pre>
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