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217 lines
9.1 KiB
HTML
4 years ago
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<title>fpclassify (LIBM)</title>
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<a name="fpclassify"></a>
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<div class="header">
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<p>
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Next: <a href="ldexp.html#ldexp" accesskey="n" rel="next">ldexp</a>, Previous: <a href="isgreater.html#isgreater" accesskey="p" rel="prev">isgreater</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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<hr>
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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>
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<h3 class="section">1.32 <code>fpclassify</code>, <code>isfinite</code>, <code>isinf</code>, <code>isnan</code>, and <code>isnormal</code>—floating-point classification macros; <code>finite</code>, <code>finitef</code>, <code>isinf</code>, <code>isinff</code>, <code>isnan</code>, <code>isnanf</code>—test for exceptional numbers</h3>
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<a name="index-fpclassify"></a>
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<a name="index-isfinite"></a>
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<a name="index-isinf"></a>
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<a name="index-isnan"></a>
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<a name="index-isnormal"></a>
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<a name="index-isnan-1"></a>
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<a name="index-isinf-1"></a>
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<a name="index-finite"></a>
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<a name="index-isnanf"></a>
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<a name="index-isinff"></a>
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<a name="index-finitef"></a>
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<p><strong>Synopsis</strong>
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</p><div class="example">
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<pre class="example">[C99 standard macros:]
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#include <math.h>
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int fpclassify(real-floating <var>x</var>);
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int isfinite(real-floating <var>x</var>);
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int isinf(real-floating <var>x</var>);
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int isnan(real-floating <var>x</var>);
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int isnormal(real-floating <var>x</var>);
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[Archaic SUSv2 functions:]
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#include <math.h>
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int isnan(double <var>arg</var>);
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int isinf(double <var>arg</var>);
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int finite(double <var>arg</var>);
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int isnanf(float <var>arg</var>);
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int isinff(float <var>arg</var>);
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int finitef(float <var>arg</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>fpclassify</code>, <code>isfinite</code>, <code>isinf</code>, <code>isnan</code>, and <code>isnormal</code> are macros
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defined for use in classifying floating-point numbers. This is a help because
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of special "values" like NaN and infinities. In the synopses shown,
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"real-floating" indicates that the argument is an expression of real floating
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type. These function-like macros are C99 and POSIX-compliant, and should be
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used instead of the now-archaic SUSv2 functions.
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</p>
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<p>The <code>fpclassify</code> macro classifies its argument value as NaN, infinite, normal,
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subnormal, zero, or into another implementation-defined category. First, an
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argument represented in a format wider than its semantic type is converted to
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its semantic type. Then classification is based on the type of the argument.
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The <code>fpclassify</code> macro returns the value of the number classification macro
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appropriate to the value of its argument:
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</p>
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<dl compact="compact">
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<dt><code>FP_INFINITE</code></dt>
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<dd><p><var>x</var> is either plus or minus infinity;
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</p></dd>
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<dt><code>FP_NAN</code></dt>
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<dd><p><var>x</var> is "Not A Number" (plus or minus);
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</p></dd>
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<dt><code>FP_NORMAL</code></dt>
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<dd><p><var>x</var> is a "normal" number (i.e. is none of the other special forms);
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</p></dd>
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<dt><code>FP_SUBNORMAL</code></dt>
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<dd><p><var>x</var> is too small be stored as a regular normalized number (i.e. loss of precision is likely); or
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</p></dd>
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<dt><code>FP_ZERO</code></dt>
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<dd><p><var>x</var> is 0 (either plus or minus).
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</p></dd>
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</dl>
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<p>The "<code>is</code>" set of macros provide a useful set of shorthand ways for
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classifying floating-point numbers, providing the following equivalent
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relations:
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</p>
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<dl compact="compact">
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<dt><code><code>isfinite</code>(<var>x</var>)</code></dt>
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<dd><p>returns non-zero if <var>x</var> is finite. (It is equivalent to
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(<code>fpclassify</code>(<var>x</var>) != FP_INFINITE && <code>fpclassify</code>(<var>x</var>) != FP_NAN).)
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</p>
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</dd>
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<dt><code><code>isinf</code>(<var>x</var>)</code></dt>
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<dd><p>returns non-zero if <var>x</var> is infinite. (It is equivalent to
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(<code>fpclassify</code>(<var>x</var>) == FP_INFINITE).)
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</p>
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</dd>
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<dt><code><code>isnan</code>(<var>x</var>)</code></dt>
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<dd><p>returns non-zero if <var>x</var> is NaN. (It is equivalent to
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(<code>fpclassify</code>(<var>x</var>) == FP_NAN).)
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</p>
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</dd>
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<dt><code><code>isnormal</code>(<var>x</var>)</code></dt>
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<dd><p>returns non-zero if <var>x</var> is normal. (It is equivalent to
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(<code>fpclassify</code>(<var>x</var>) == FP_NORMAL).)
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</p></dd>
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</dl>
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<p>The archaic SUSv2 functions provide information on the floating-point
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argument supplied.
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</p>
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<p>There are five major number formats ("exponent" referring to the
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biased exponent in the binary-encoded number):
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</p><dl compact="compact">
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<dt><code>zero</code></dt>
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<dd><p>A number which contains all zero bits, excluding the sign bit.
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</p></dd>
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<dt><code>subnormal</code></dt>
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<dd><p>A number with a zero exponent but a nonzero fraction.
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</p></dd>
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<dt><code>normal</code></dt>
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<dd><p>A number with an exponent and a fraction.
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</p></dd>
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<dt><code>infinity</code></dt>
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<dd><p>A number with an all 1’s exponent and a zero fraction.
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</p></dd>
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<dt><code>NAN</code></dt>
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<dd><p>A number with an all 1’s exponent and a nonzero fraction.
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</p>
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</dd>
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</dl>
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<p><code>isnan</code> returns 1 if the argument is a nan. <code>isinf</code>
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returns 1 if the argument is infinity. <code>finite</code> returns 1 if the
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argument is zero, subnormal or normal.
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The <code>isnanf</code>, <code>isinff</code> and <code>finitef</code> functions perform the same
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operations as their <code>isnan</code>, <code>isinf</code> and <code>finite</code>
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counterparts, but on single-precision floating-point numbers.
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</p>
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<p>It should be noted that the C99 standard dictates that <code>isnan</code>
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and <code>isinf</code> are macros that operate on multiple types of
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floating-point. The SUSv2 standard declares <code>isnan</code> as
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a function taking double. Newlib has decided to declare
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them both as functions and as macros in math.h to
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maintain backward compatibility.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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The fpclassify macro returns the value corresponding to the appropriate FP_ macro.<br>
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The isfinite macro returns nonzero if <var>x</var> is finite, else 0.<br>
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The isinf macro returns nonzero if <var>x</var> is infinite, else 0.<br>
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The isnan macro returns nonzero if <var>x</var> is an NaN, else 0.<br>
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The isnormal macro returns nonzero if <var>x</var> has a normal value, else 0.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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math.h macros are C99, POSIX.1-2001.
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</p>
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<p>The functions originate from BSD; isnan was listed in the X/Open
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Portability Guide and Single Unix Specification, but was dropped when
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the macro was standardized in POSIX.1-2001.
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</p>
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<br>
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<hr>
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<p>
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Next: <a href="ldexp.html#ldexp" accesskey="n" rel="next">ldexp</a>, Previous: <a href="isgreater.html#isgreater" accesskey="p" rel="prev">isgreater</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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