92 lines
3.8 KiB
HTML
92 lines
3.8 KiB
HTML
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<h1>Fast atoi() in C and C++</h1>
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<div style="text-align: center !important;">
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<p>
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2022-01-20 17:10:10 EET |
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<a href=".."> back </a>
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<p>
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<code>std::atoi</code> (in C++) is fast on its own but can be slow so
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for stuff you need speed you can use this:
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</p>
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<ul>
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<li>Option one</li>
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</ul>
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<pre><code><span class="hljs-function"><span class="hljs-keyword">int</span> <span class="hljs-title">fast_atoi</span>(<span class="hljs-params"><span class="hljs-keyword">char</span> *int_string</span>) </span>{
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<span class="hljs-keyword">int</span> <span class="hljs-keyword">value</span> = <span class="hljs-number">0</span>;
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<span class="hljs-keyword">while</span> (*int_string && *int_string >= <span class="hljs-string">'0'</span> && *int_string <= <span class="hljs-string">'9'</span>)
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<span class="hljs-keyword">value</span> = <span class="hljs-keyword">value</span> * <span class="hljs-number">10</span> + (*int_string++ - <span class="hljs-string">'0'</span>);
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<span class="hljs-keyword">return</span> <span class="hljs-keyword">value</span>;
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}
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</code></pre>
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<p>
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This requires no headers, just pure C (also valid in C++), you can put
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this into your code and it will just work!
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</p>
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<ul>
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<li>Option two</li>
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</ul>
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<pre><code><span class="hljs-meta">#include <assert.h></span>
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<span class="hljs-function"><span class="hljs-keyword">int</span> <span class="hljs-title">fast_atoi</span>(<span class="hljs-params"><span class="hljs-keyword">char</span> *int_string</span>) </span>{
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<span class="hljs-keyword">int</span> <span class="hljs-keyword">value</span> = <span class="hljs-number">0</span>;
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<span class="hljs-keyword">while</span> (*int_string) {
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<span class="hljs-keyword">if</span> (!(*int_string >= <span class="hljs-string">'0'</span> && *int_string <= <span class="hljs-string">'9'</span>))
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assert(<span class="hljs-number">0</span> && <span class="hljs-string">"atoi(): invalid int_string"</span>);
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<span class="hljs-keyword">value</span> = <span class="hljs-keyword">value</span> * <span class="hljs-number">10</span> + (*int_string++ - <span class="hljs-string">'0'</span>);
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}
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<span class="hljs-keyword">return</span> <span class="hljs-keyword">value</span>;
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}
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</code></pre>
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<p>
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This option is throws an assertion error if it encounters an invalid
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string but this requires <code>assert.h</code> as a dependency.
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</p>
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<p>
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In C++ <code>assert.h</code> should be replaced with
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<code>cassert</code>.
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</p>
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