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<a name="ilogb_002c-ilogbf_002d_002d_002dget-exponent-of-floating_002dpoint-number"></a>
<h3 class="section">1.29 <code>ilogb</code>, <code>ilogbf</code>&mdash;get exponent of floating-point number</h3>
<a name="index-ilogb"></a>
<a name="index-ilogbf"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;math.h&gt;
int ilogb(double <var>val</var>);
int ilogbf(float <var>val</var>);

</pre></div>
<p><strong>Description</strong><br>
</p>
<p>All nonzero, normal numbers can be described as <var>m</var> *
2**<var>p</var>.  <code>ilogb</code> and <code>ilogbf</code> examine the argument
<var>val</var>, and return <var>p</var>.  The functions <code>frexp</code> and
<code>frexpf</code> are similar to <code>ilogb</code> and <code>ilogbf</code>, but also
return <var>m</var>.
</p>
<br>
<p><strong>Returns</strong><br>
</p>
<p><code>ilogb</code> and <code>ilogbf</code> return the power of two used to form the
floating-point argument.
If <var>val</var> is <code>0</code>, they return <code>FP_ILOGB0</code>.
If <var>val</var> is infinite, they return <code>INT_MAX</code>.
If <var>val</var> is NaN, they return <code>FP_ILOGBNAN</code>.
(<code>FP_ILOGB0</code> and <code>FP_ILOGBNAN</code> are defined in math.h, but in turn are
defined as INT_MIN or INT_MAX from limits.h.  The value of FP_ILOGB0 may be
either INT_MIN or -INT_MAX.  The value of FP_ILOGBNAN may be either INT_MAX or
INT_MIN.)
</p>

<br>
<p><strong>Portability</strong><br>
C99, POSIX
</p>
<br>


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