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<h1 class='fqn'><span class='in-band'>Function <a href='index.html'>hamming</a>::<wbr><a class='fn' href=''>distance</a></span><span class='out-of-band'><span id='render-detail'>
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</span><a id='src-176' class='srclink' href='../src/hamming/distance_.rs.html#202-206' title='goto source code'>[src]</a></span></h1>
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<pre class='rust fn'>pub fn distance(x: <a class='primitive' href='https://doc.rust-lang.org/nightly/std/primitive.slice.html'>&[</a><a class='primitive' href='https://doc.rust-lang.org/nightly/std/primitive.u8.html'>u8</a><a class='primitive' href='https://doc.rust-lang.org/nightly/std/primitive.slice.html'>]</a>, y: <a class='primitive' href='https://doc.rust-lang.org/nightly/std/primitive.slice.html'>&[</a><a class='primitive' href='https://doc.rust-lang.org/nightly/std/primitive.u8.html'>u8</a><a class='primitive' href='https://doc.rust-lang.org/nightly/std/primitive.slice.html'>]</a>) -> <a class='primitive' href='https://doc.rust-lang.org/nightly/std/primitive.u64.html'>u64</a></pre><div class='docblock'><p>Computes the bitwise <a href="https://en.wikipedia.org/wiki/Hamming_distance">Hamming
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distance</a> between
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<code>x</code> and <code>y</code>, that is, the number of bits where <code>x</code> and <code>y</code> differ,
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or, the number of set bits in the xor of <code>x</code> and <code>y</code>.</p>
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<p>When <code>x</code> and <code>y</code> have the same 8-byte alignment, this uses
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<code>distance_fast</code>, a highly optimised version of the following naive
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version:</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>fn</span> <span class='ident'>naive</span>(<span class='ident'>x</span>: <span class='kw-2'>&</span>[<span class='ident'>u8</span>], <span class='ident'>y</span>: <span class='kw-2'>&</span>[<span class='ident'>u8</span>]) <span class='op'>-></span> <span class='ident'>u64</span> {
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<span class='ident'>x</span>.<span class='ident'>iter</span>().<span class='ident'>zip</span>(<span class='ident'>y</span>).<span class='ident'>fold</span>(<span class='number'>0</span>, <span class='op'>|</span><span class='ident'>a</span>, (<span class='ident'>b</span>, <span class='ident'>c</span>)<span class='op'>|</span> <span class='ident'>a</span> <span class='op'>+</span> (<span class='op'>*</span><span class='ident'>b</span> <span class='op'>^</span> <span class='op'>*</span><span class='ident'>c</span>).<span class='ident'>count_ones</span>() <span class='kw'>as</span> <span class='ident'>u64</span>)
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}</pre>
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<p>If alignments differ, a slower but less restrictive algorithm is
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used.</p>
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<p>It is essentially guaranteed that <code>x</code> and <code>y</code> will have the same
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8-byte alignment if they are both just <code>Vec<u8></code>s of non-trivial
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length (e.g. larger than 8) as in the example below.</p>
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<h1 id='panics' class='section-header'><a href='#panics'>Panics</a></h1>
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<p><code>x</code> and <code>y</code> must have the same length, or else <code>distance</code> panics.</p>
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<h1 id='performance-comparison' class='section-header'><a href='#performance-comparison'>Performance Comparison</a></h1>
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<table>
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<thead>
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<tr>
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<th style="text-align: right">length</th>
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<th style="text-align: right"><code>naive</code> (ns)</th>
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<th style="text-align: right"><code>distance</code> (ns)</th>
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<th style="text-align: right"><code>naive</code>/<code>distance</code></th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td style="text-align: right">1</td>
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<td style="text-align: right">5</td>
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<td style="text-align: right">6</td>
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<td style="text-align: right">0.83</td>
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</tr>
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<tr>
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<td style="text-align: right">10</td>
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<td style="text-align: right">44</td>
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<td style="text-align: right">45</td>
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<td style="text-align: right">0.97</td>
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</tr>
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<tr>
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<td style="text-align: right">100</td>
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<td style="text-align: right">461</td>
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<td style="text-align: right">473</td>
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<td style="text-align: right">0.97</td>
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</tr>
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<tr>
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<td style="text-align: right">1,000</td>
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<td style="text-align: right">4,510</td>
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<td style="text-align: right">397</td>
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<td style="text-align: right">11</td>
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</tr>
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<tr>
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<td style="text-align: right">10,000</td>
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<td style="text-align: right">46,700</td>
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<td style="text-align: right">2,740</td>
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<td style="text-align: right">17</td>
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</tr>
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<tr>
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<td style="text-align: right">100,000</td>
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<td style="text-align: right">45,600</td>
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<td style="text-align: right">20,400</td>
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<td style="text-align: right">22</td>
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</tr>
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<tr>
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<td style="text-align: right">1,000,000</td>
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<td style="text-align: right">4,590,000</td>
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<td style="text-align: right">196,000</td>
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<td style="text-align: right">23</td>
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</tr>
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</tbody>
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</table>
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<p>The benchmarks ensured that <code>x</code> and <code>y</code> had the same alignment.</p>
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<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>let</span> <span class='ident'>x</span> <span class='op'>=</span> <span class='macro'>vec</span><span class='macro'>!</span>[<span class='number'>0xFF</span>; <span class='number'>1000</span>];
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<span class='kw'>let</span> <span class='ident'>y</span> <span class='op'>=</span> <span class='macro'>vec</span><span class='macro'>!</span>[<span class='number'>0</span>; <span class='number'>1000</span>];
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<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>hamming</span>::<span class='ident'>distance</span>(<span class='kw-2'>&</span><span class='ident'>x</span>, <span class='kw-2'>&</span><span class='ident'>y</span>), <span class='number'>8</span> <span class='op'>*</span> <span class='number'>1000</span>);</pre>
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