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<title>log1p (LIBM)</title>
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<p>
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Next: <a href="log2.html#log2" accesskey="n" rel="next">log2</a>, Previous: <a href="log10.html#log10" accesskey="p" rel="prev">log10</a>, Up: <a href="Math.html#Math" accesskey="u" rel="up">Math</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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<a name="log1p_002c-log1pf_002d_002d_002dlog-of-1-_002b-x"></a>
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<h3 class="section">1.36 <code>log1p</code>, <code>log1pf</code>—log of <code>1 + <var>x</var></code></h3>
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<a name="index-log1p"></a>
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<a name="index-log1pf"></a>
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<p><strong>Synopsis</strong>
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</p><div class="example">
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<pre class="example">#include <math.h>
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double log1p(double <var>x</var>);
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float log1pf(float <var>x</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>log1p</code> calculates
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the natural logarithm of <code>1+<var>x</var></code>. You can use <code>log1p</code> rather
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than ‘<code>log(1+<var>x</var>)</code>’ for greater precision when <var>x</var> is very
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small.
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</p>
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<p><code>log1pf</code> calculates the same thing, but accepts and returns
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<code>float</code> values rather than <code>double</code>.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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<code>log1p</code> returns a <code>double</code>, the natural log of <code>1+<var>x</var></code>.
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<code>log1pf</code> returns a <code>float</code>, the natural log of <code>1+<var>x</var></code>.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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Neither <code>log1p</code> nor <code>log1pf</code> is required by ANSI C or by the System V
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Interface Definition (Issue 2).
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