You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
105 lines
4.2 KiB
HTML
105 lines
4.2 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>logb (LIBM)</title>
|
|
|
|
<meta name="description" content="logb (LIBM)">
|
|
<meta name="keywords" content="logb (LIBM)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<link href="index.html#Top" rel="start" title="Top">
|
|
<link href="Document-Index.html#Document-Index" rel="index" title="Document Index">
|
|
<link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Math.html#Math" rel="up" title="Math">
|
|
<link href="lrint.html#lrint" rel="next" title="lrint">
|
|
<link href="log2.html#log2" rel="prev" title="log2">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
|
blockquote.smallquotation {font-size: smaller}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
div.smalldisplay {margin-left: 3.2em}
|
|
div.smallexample {margin-left: 3.2em}
|
|
div.smalllisp {margin-left: 3.2em}
|
|
kbd {font-style: oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
|
pre.smallexample {font-size: smaller}
|
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
|
pre.smalllisp {font-size: smaller}
|
|
span.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<a name="logb"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="lrint.html#lrint" accesskey="n" rel="next">lrint</a>, Previous: <a href="log2.html#log2" accesskey="p" rel="prev">log2</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>
|
|
</div>
|
|
<hr>
|
|
<a name="logb_002c-logbf_002d_002d_002dget-exponent-of-floating_002dpoint-number"></a>
|
|
<h3 class="section">1.38 <code>logb</code>, <code>logbf</code>—get exponent of floating-point number</h3>
|
|
<a name="index-logb"></a>
|
|
<a name="index-logbf"></a>
|
|
<p><strong>Synopsis</strong>
|
|
</p><div class="example">
|
|
<pre class="example">#include <math.h>
|
|
double logb(double <var>x</var>);
|
|
float logbf(float <var>x</var>);
|
|
|
|
</pre></div>
|
|
<p><strong>Description</strong><br>
|
|
The <code>logb</code> functions extract the exponent of <var>x</var>, as a signed integer value
|
|
in floating-point format. If <var>x</var> is subnormal it is treated as though it were
|
|
normalized; thus, for positive finite <var>x</var>,
|
|
1 <= (<var>x</var> * FLT_RADIX to the power (-logb(<var>x</var>))) < FLT_RADIX.
|
|
A domain error may occur if the argument is zero.
|
|
In this floating-point implementation, FLT_RADIX is 2. Which also means
|
|
that for finite <var>x</var>, <code>logb</code>(<var>x</var>) = <code>floor</code>(<code>log2</code>(<code>fabs</code>(<var>x</var>))).
|
|
</p>
|
|
<p>All nonzero, normal numbers can be described as
|
|
<var>m</var> * 2**<var>p</var>, where 1.0 <= <var>m</var> < 2.0.
|
|
The <code>logb</code> functions examine the argument <var>x</var>, and return <var>p</var>.
|
|
The <code>frexp</code> functions are similar to the <code>logb</code> functions, but
|
|
returning <var>m</var> adjusted to the interval [.5, 1) or 0, and <var>p</var>+1.
|
|
</p>
|
|
<br>
|
|
<p><strong>Returns</strong><br>
|
|
When <var>x</var> is:<br>
|
|
+inf or -inf, +inf is returned;<br>
|
|
NaN, NaN is returned;<br>
|
|
0, -inf is returned, and the divide-by-zero exception is raised;<br>
|
|
otherwise, the <code>logb</code> functions return the signed exponent of <var>x</var>.
|
|
</p>
|
|
<br>
|
|
<p><strong>Portability</strong><br>
|
|
ANSI C, POSIX
|
|
</p>
|
|
<br>
|
|
<p><strong>See Also</strong><br>
|
|
frexp, ilogb
|
|
</p>
|
|
<br>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|