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<a name="expm1_002c-expm1f_002d_002d_002dexponential-minus-1"></a>
<h3 class="section">1.18 <code>expm1</code>, <code>expm1f</code>&mdash;exponential minus 1</h3>
<a name="index-expm1"></a>
<a name="index-expm1f"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;math.h&gt;
double expm1(double <var>x</var>);
float expm1f(float <var>x</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>expm1</code> and <code>expm1f</code> calculate the exponential of <var>x</var>
and subtract 1, that is,
e raised to the power <var>x</var> minus 1 (where e
is the base of the natural system of logarithms, approximately
2.71828).  The result is accurate even for small values of
<var>x</var>, where using <code>exp(<var>x</var>)-1</code> would lose many
significant digits.
</p>
<br>
<p><strong>Returns</strong><br>
e raised to the power <var>x</var>, minus 1.
</p>
<br>
<p><strong>Portability</strong><br>
Neither <code>expm1</code> nor <code>expm1f</code> is required by ANSI C or by
the System V Interface Definition (Issue 2).
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