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<a name="fpclassify_002c-isfinite_002c-isinf_002c-isnan_002c-and-isnormal_002d_002d_002dfloating_002dpoint-classification-macros_003b-finite_002c-finitef_002c-isinf_002c-isinff_002c-isnan_002c-isnanf_002d_002d_002dtest-for-exceptional-numbers"></a>
<h3 class="section">1.32 <code>fpclassify</code>, <code>isfinite</code>, <code>isinf</code>, <code>isnan</code>, and <code>isnormal</code>&mdash;floating-point classification macros; <code>finite</code>, <code>finitef</code>, <code>isinf</code>, <code>isinff</code>, <code>isnan</code>, <code>isnanf</code>&mdash;test for exceptional numbers</h3>
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<a name="index-isnan"></a>
<a name="index-isnormal"></a>
<a name="index-isnan-1"></a>
<a name="index-isinf-1"></a>
<a name="index-finite"></a>
<a name="index-isnanf"></a>
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<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">[C99 standard macros:]
#include &lt;math.h&gt;
int fpclassify(real-floating <var>x</var>);
int isfinite(real-floating <var>x</var>);
int isinf(real-floating <var>x</var>);
int isnan(real-floating <var>x</var>);
int isnormal(real-floating <var>x</var>);

[Archaic SUSv2 functions:]
#include &lt;math.h&gt;
int isnan(double <var>arg</var>);
int isinf(double <var>arg</var>);
int finite(double <var>arg</var>);
int isnanf(float <var>arg</var>);
int isinff(float <var>arg</var>);
int finitef(float <var>arg</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>fpclassify</code>, <code>isfinite</code>, <code>isinf</code>, <code>isnan</code>, and <code>isnormal</code> are macros
defined for use in classifying floating-point numbers.  This is a help because
of special &quot;values&quot; like NaN and infinities.  In the synopses shown,
&quot;real-floating&quot; indicates that the argument is an expression of real floating
type.  These function-like macros are C99 and POSIX-compliant, and should be
used instead of the now-archaic SUSv2 functions.
</p>
<p>The <code>fpclassify</code> macro classifies its argument value as NaN, infinite, normal,
subnormal, zero, or into another implementation-defined category.  First, an
argument represented in a format wider than its semantic type is converted to
its semantic type.  Then classification is based on the type of the argument.
The <code>fpclassify</code> macro returns the value of the number classification macro
appropriate to the value of its argument:
</p>
<dl compact="compact">
<dt><code>FP_INFINITE</code></dt>
<dd><p><var>x</var> is either plus or minus infinity;
</p></dd>
<dt><code>FP_NAN</code></dt>
<dd><p><var>x</var> is &quot;Not A Number&quot; (plus or minus);
</p></dd>
<dt><code>FP_NORMAL</code></dt>
<dd><p><var>x</var> is a &quot;normal&quot; number (i.e. is none of the other special forms);
</p></dd>
<dt><code>FP_SUBNORMAL</code></dt>
<dd><p><var>x</var> is too small be stored as a regular normalized number (i.e. loss of precision is likely); or
</p></dd>
<dt><code>FP_ZERO</code></dt>
<dd><p><var>x</var> is 0 (either plus or minus).
</p></dd>
</dl>


<p>The &quot;<code>is</code>&quot; set of macros provide a useful set of shorthand ways for
classifying floating-point numbers, providing the following equivalent
relations:
</p>
<dl compact="compact">
<dt><code><code>isfinite</code>(<var>x</var>)</code></dt>
<dd><p>returns non-zero if <var>x</var> is finite.  (It is equivalent to
(<code>fpclassify</code>(<var>x</var>) != FP_INFINITE  &amp;&amp;  <code>fpclassify</code>(<var>x</var>) != FP_NAN).)
</p>
</dd>
<dt><code><code>isinf</code>(<var>x</var>)</code></dt>
<dd><p>returns non-zero if <var>x</var> is infinite.  (It is equivalent to
(<code>fpclassify</code>(<var>x</var>) == FP_INFINITE).)
</p>
</dd>
<dt><code><code>isnan</code>(<var>x</var>)</code></dt>
<dd><p>returns non-zero if <var>x</var> is NaN.  (It is equivalent to
(<code>fpclassify</code>(<var>x</var>) == FP_NAN).)
</p>
</dd>
<dt><code><code>isnormal</code>(<var>x</var>)</code></dt>
<dd><p>returns non-zero if <var>x</var> is normal.  (It is equivalent to
(<code>fpclassify</code>(<var>x</var>) == FP_NORMAL).)
</p></dd>
</dl>


<p>The archaic SUSv2 functions provide information on the floating-point
argument supplied.
</p>
<p>There are five major number formats (&quot;exponent&quot; referring to the
biased exponent in the binary-encoded number):
</p><dl compact="compact">
<dt><code>zero</code></dt>
<dd><p>A number which contains all zero bits, excluding the sign bit.
</p></dd>
<dt><code>subnormal</code></dt>
<dd><p>A number with a zero exponent but a nonzero fraction.
</p></dd>
<dt><code>normal</code></dt>
<dd><p>A number with an exponent and a fraction.
</p></dd>
<dt><code>infinity</code></dt>
<dd><p>A number with an all 1&rsquo;s exponent and a zero fraction.
</p></dd>
<dt><code>NAN</code></dt>
<dd><p>A number with an all 1&rsquo;s exponent and a nonzero fraction.
</p>
</dd>
</dl>


<p><code>isnan</code> returns 1 if the argument is a nan. <code>isinf</code>
returns 1 if the argument is infinity.  <code>finite</code> returns 1 if the
argument is zero, subnormal or normal.
The <code>isnanf</code>, <code>isinff</code> and <code>finitef</code> functions perform the same
operations as their <code>isnan</code>, <code>isinf</code> and <code>finite</code>
counterparts, but on single-precision floating-point numbers.
</p>
<p>It should be noted that the C99 standard dictates that <code>isnan</code>
and <code>isinf</code> are macros that operate on multiple types of
floating-point.  The SUSv2 standard declares <code>isnan</code> as
a function taking double.  Newlib has decided to declare
them both as functions and as macros in math.h to
maintain backward compatibility.
</p>
<br>
<p><strong>Returns</strong><br>
The fpclassify macro returns the value corresponding to the appropriate FP_ macro.<br>
The isfinite macro returns nonzero if <var>x</var> is finite, else 0.<br>
The isinf macro returns nonzero if <var>x</var> is infinite, else 0.<br>
The isnan macro returns nonzero if <var>x</var> is an NaN, else 0.<br>
The isnormal macro returns nonzero if <var>x</var> has a normal value, else 0.
</p>
<br>
<p><strong>Portability</strong><br>
math.h macros are C99, POSIX.1-2001.
</p>
<p>The functions originate from BSD; isnan was listed in the X/Open
Portability Guide and Single Unix Specification, but was dropped when
the macro was standardized in POSIX.1-2001.
</p>
<br>
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