<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="theme-color" content="#375EAB">
<title>crc32 - The Go Programming Language</title>
<link type="text/css" rel="stylesheet" href="../../../lib/godoc/style.css">
<link rel="stylesheet" href="../../../lib/godoc/jquery.treeview.css">
<script type="text/javascript">window.initFuncs = [];</script>
</head>
<body>
<div id='lowframe' style="position: fixed; bottom: 0; left: 0; height: 0; width: 100%; border-top: thin solid grey; background-color: white; overflow: auto;">
...
</div><!-- #lowframe -->
<div id="topbar" class="wide"><div class="container">
<div class="top-heading" id="heading-wide"><a href="http://localhost:6060/">The Go Programming Language</a></div>
<div class="top-heading" id="heading-narrow"><a href="http://localhost:6060/">Go</a></div>
<a href="index.html#" id="menu-button"><span id="menu-button-arrow">▽</span></a>
<form method="GET" action="http://localhost:6060/search">
<div id="menu">
<a href="http://localhost:6060/doc/">Documents</a>
<a href="http://localhost:6060/pkg/">Packages</a>
<a href="http://localhost:6060/project/">The Project</a>
<a href="http://localhost:6060/help/">Help</a>
<a href="http://localhost:6060/blog/">Blog</a>
<input type="text" id="search" name="q" class="inactive" value="Search" placeholder="Search">
</div>
</form>
</div></div>
<div id="page" class="wide">
<div class="container">
<h1>Package crc32</h1>
<div id="nav"></div>
<!--
Copyright 2009 The Go Authors. All rights reserved.
Use of this source code is governed by a BSD-style
license that can be found in the LICENSE file.
-->
<!--
Note: Static (i.e., not template-generated) href and id
attributes start with "pkg-" to make it impossible for
them to conflict with generated attributes (some of which
correspond to Go identifiers).
-->
<script type='text/javascript'>
document.ANALYSIS_DATA = null;
document.CALLGRAPH = null;
</script>
<div id="short-nav">
<dl>
<dd><code>import "hash/crc32"</code></dd>
</dl>
<dl>
<dd><a href="index.html#pkg-overview" class="overviewLink">Overview</a></dd>
<dd><a href="index.html#pkg-index" class="indexLink">Index</a></dd>
<dd><a href="index.html#pkg-examples" class="examplesLink">Examples</a></dd>
</dl>
</div>
<!-- The package's Name is printed as title by the top-level template -->
<div id="pkg-overview" class="toggleVisible">
<div class="collapsed">
<h2 class="toggleButton" title="Click to show Overview section">Overview ▹</h2>
</div>
<div class="expanded">
<h2 class="toggleButton" title="Click to hide Overview section">Overview ▾</h2>
<p>
Package crc32 implements the 32-bit cyclic redundancy check, or CRC-32,
checksum. See <a href="http://en.wikipedia.org/wiki/Cyclic_redundancy_check">http://en.wikipedia.org/wiki/Cyclic_redundancy_check</a> for
information.
</p>
<p>
Polynomials are represented in LSB-first form also known as reversed representation.
</p>
<p>
See <a href="http://en.wikipedia.org/wiki/Mathematics_of_cyclic_redundancy_checks#Reversed_representations_and_reciprocal_polynomials">http://en.wikipedia.org/wiki/Mathematics_of_cyclic_redundancy_checks#Reversed_representations_and_reciprocal_polynomials</a>
for information.
</p>
</div>
</div>
<div id="pkg-index" class="toggleVisible">
<div class="collapsed">
<h2 class="toggleButton" title="Click to show Index section">Index ▹</h2>
</div>
<div class="expanded">
<h2 class="toggleButton" title="Click to hide Index section">Index ▾</h2>
<!-- Table of contents for API; must be named manual-nav to turn off auto nav. -->
<div id="manual-nav">
<dl>
<dd><a href="index.html#pkg-constants">Constants</a></dd>
<dd><a href="index.html#pkg-variables">Variables</a></dd>
<dd><a href="index.html#Checksum">func Checksum(data []byte, tab *Table) uint32</a></dd>
<dd><a href="index.html#ChecksumIEEE">func ChecksumIEEE(data []byte) uint32</a></dd>
<dd><a href="index.html#New">func New(tab *Table) hash.Hash32</a></dd>
<dd><a href="index.html#NewIEEE">func NewIEEE() hash.Hash32</a></dd>
<dd><a href="index.html#Update">func Update(crc uint32, tab *Table, p []byte) uint32</a></dd>
<dd><a href="index.html#Table">type Table</a></dd>
<dd> <a href="index.html#MakeTable">func MakeTable(poly uint32) *Table</a></dd>
</dl>
</div><!-- #manual-nav -->
<div id="pkg-examples">
<h4>Examples</h4>
<dl>
<dd><a class="exampleLink" href="index.html#example_MakeTable">MakeTable</a></dd>
</dl>
</div>
<h4>Package files</h4>
<p>
<span style="font-size:90%">
<a href="http://localhost:6060/src/hash/crc32/crc32.go">crc32.go</a>
<a href="http://localhost:6060/src/hash/crc32/crc32_amd64.go">crc32_amd64.go</a>
</span>
</p>
</div><!-- .expanded -->
</div><!-- #pkg-index -->
<div id="pkg-callgraph" class="toggle" style="display: none">
<div class="collapsed">
<h2 class="toggleButton" title="Click to show Internal Call Graph section">Internal call graph ▹</h2>
</div> <!-- .expanded -->
<div class="expanded">
<h2 class="toggleButton" title="Click to hide Internal Call Graph section">Internal call graph ▾</h2>
<p>
In the call graph viewer below, each node
is a function belonging to this package
and its children are the functions it
calls—perhaps dynamically.
</p>
<p>
The root nodes are the entry points of the
package: functions that may be called from
outside the package.
There may be non-exported or anonymous
functions among them if they are called
dynamically from another package.
</p>
<p>
Click a node to visit that function's source code.
From there you can visit its callers by
clicking its declaring <code>func</code>
token.
</p>
<p>
Functions may be omitted if they were
determined to be unreachable in the
particular programs or tests that were
analyzed.
</p>
<!-- Zero means show all package entry points. -->
<ul style="margin-left: 0.5in" id="callgraph-0" class="treeview"></ul>
</div>
</div> <!-- #pkg-callgraph -->
<h2 id="pkg-constants">Constants</h2>
<pre>const (
<span class="comment">// IEEE is by far and away the most common CRC-32 polynomial.</span>
<span class="comment">// Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, ...</span>
<span id="IEEE">IEEE</span> = 0xedb88320
<span class="comment">// Castagnoli's polynomial, used in iSCSI.</span>
<span class="comment">// Has better error detection characteristics than IEEE.</span>
<span class="comment">// http://dx.doi.org/10.1109/26.231911</span>
<span id="Castagnoli">Castagnoli</span> = 0x82f63b78
<span class="comment">// Koopman's polynomial.</span>
<span class="comment">// Also has better error detection characteristics than IEEE.</span>
<span class="comment">// http://dx.doi.org/10.1109/DSN.2002.1028931</span>
<span id="Koopman">Koopman</span> = 0xeb31d82e
)</pre>
<p>
Predefined polynomials.
</p>
<pre>const <span id="Size">Size</span> = 4</pre>
<p>
The size of a CRC-32 checksum in bytes.
</p>
<h2 id="pkg-variables">Variables</h2>
<pre>var <span id="IEEETable">IEEETable</span> = makeTable(<a href="index.html#IEEE">IEEE</a>)</pre>
<p>
IEEETable is the table for the IEEE polynomial.
</p>
<h2 id="Checksum">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=4825:4870#L167">Checksum</a></h2>
<pre>func Checksum(data []<a href="../../builtin/index.html#byte">byte</a>, tab *<a href="index.html#Table">Table</a>) <a href="../../builtin/index.html#uint32">uint32</a></pre>
<p>
Checksum returns the CRC-32 checksum of data
using the polynomial represented by the Table.
</p>
<h2 id="ChecksumIEEE">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=4986:5023#L171">ChecksumIEEE</a></h2>
<pre>func ChecksumIEEE(data []<a href="../../builtin/index.html#byte">byte</a>) <a href="../../builtin/index.html#uint32">uint32</a></pre>
<p>
ChecksumIEEE returns the CRC-32 checksum of data
using the IEEE polynomial.
</p>
<h2 id="New">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=3160:3192#L107">New</a></h2>
<pre>func New(tab *<a href="index.html#Table">Table</a>) <a href="../index.html">hash</a>.<a href="../index.html#Hash32">Hash32</a></pre>
<p>
New creates a new hash.Hash32 computing the CRC-32 checksum
using the polynomial represented by the Table.
Its Sum method will lay the value out in big-endian byte order.
</p>
<h2 id="NewIEEE">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=3385:3411#L112">NewIEEE</a></h2>
<pre>func NewIEEE() <a href="../index.html">hash</a>.<a href="../index.html#Hash32">Hash32</a></pre>
<p>
NewIEEE creates a new hash.Hash32 computing the CRC-32 checksum
using the IEEE polynomial.
Its Sum method will lay the value out in big-endian byte order.
</p>
<h2 id="Update">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=4236:4288#L143">Update</a></h2>
<pre>func Update(crc <a href="../../builtin/index.html#uint32">uint32</a>, tab *<a href="index.html#Table">Table</a>, p []<a href="../../builtin/index.html#byte">byte</a>) <a href="../../builtin/index.html#uint32">uint32</a></pre>
<p>
Update returns the result of adding the bytes in p to the crc.
</p>
<h2 id="Table">type <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=1266:1288#L31">Table</a></h2>
<pre>type Table [256]<a href="../../builtin/index.html#uint32">uint32</a></pre>
<p>
Table is a 256-word table representing the polynomial for efficient processing.
</p>
<h3 id="MakeTable">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=2047:2081#L56">MakeTable</a></h3>
<pre>func MakeTable(poly <a href="../../builtin/index.html#uint32">uint32</a>) *<a href="index.html#Table">Table</a></pre>
<p>
MakeTable returns a Table constructed from the specified polynomial.
The contents of this Table must not be modified.
</p>
<div id="example_MakeTable" class="toggle">
<div class="collapsed">
<p class="exampleHeading toggleButton">▹ <span class="text">Example</span></p>
</div>
<div class="expanded">
<p class="exampleHeading toggleButton">▾ <span class="text">Example</span></p>
<p>Code:</p>
<pre class="code"><span class="comment">// In this package, the CRC polynomial is represented in reversed notation,</span>
<span class="comment">// or LSB-first representation.</span>
<span class="comment">//</span>
<span class="comment">// LSB-first representation is a hexadecimal number with n bits, in which the</span>
<span class="comment">// most significant bit represents the coefficient of x⁰ and the least significant</span>
<span class="comment">// bit represents the coefficient of xⁿ⁻¹ (the coefficient for xⁿ is implicit).</span>
<span class="comment">//</span>
<span class="comment">// For example, CRC32-Q, as defined by the following polynomial,</span>
<span class="comment">// x³²+ x³¹+ x²⁴+ x²²+ x¹⁶+ x¹⁴+ x⁸+ x⁷+ x⁵+ x³+ x¹+ x⁰</span>
<span class="comment">// has the reversed notation 0b11010101100000101000001010000001, so the value</span>
<span class="comment">// that should be passed to MakeTable is 0xD5828281.</span>
crc32q := crc32.MakeTable(0xD5828281)
fmt.Printf("%08x\n", crc32.Checksum([]byte("Hello world"), crc32q))
<span class="comment"></pre>
<p>Output:</p>
<pre class="output">2964d064
</pre>
</div>
</div>
<div id="footer">
Build version go1.6.<br>
Except as <a href="https://developers.google.com/site-policies#restrictions">noted</a>,
the content of this page is licensed under the
Creative Commons Attribution 3.0 License,
and code is licensed under a <a href="http://localhost:6060/LICENSE">BSD license</a>.<br>
<a href="http://localhost:6060/doc/tos.html">Terms of Service</a> |
<a href="http://www.google.com/intl/en/policies/privacy/">Privacy Policy</a>
</div>
</div><!-- .container -->
</div><!-- #page -->
<!-- TODO(adonovan): load these from <head> using "defer" attribute? -->
<script type="text/javascript" src="../../../lib/godoc/jquery.js"></script>
<script type="text/javascript" src="../../../lib/godoc/jquery.treeview.js"></script>
<script type="text/javascript" src="../../../lib/godoc/jquery.treeview.edit.js"></script>
<script type="text/javascript" src="../../../lib/godoc/godocs.js"></script>
</body>
</html>