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<h1>Package crc32</h1>
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Copyright 2009 The Go Authors. All rights reserved.
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Use of this source code is governed by a BSD-style
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<dl>
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<dd><code>import "hash/crc32"</code></dd>
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<dd><a href="index.html#pkg-overview" class="overviewLink">Overview</a></dd>
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<h2 class="toggleButton" title="Click to hide Overview section">Overview ▾</h2>
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<p>
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Package crc32 implements the 32-bit cyclic redundancy check, or CRC-32,
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checksum. See <a href="http://en.wikipedia.org/wiki/Cyclic_redundancy_check">http://en.wikipedia.org/wiki/Cyclic_redundancy_check</a> for
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information.
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</p>
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<p>
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Polynomials are represented in LSB-first form also known as reversed representation.
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</p>
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<p>
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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>
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for information.
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<dd><a href="index.html#pkg-constants">Constants</a></dd>
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<dd><a href="index.html#pkg-variables">Variables</a></dd>
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<dd><a href="index.html#Checksum">func Checksum(data []byte, tab *Table) uint32</a></dd>
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<dd><a href="index.html#ChecksumIEEE">func ChecksumIEEE(data []byte) uint32</a></dd>
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<dd><a href="index.html#New">func New(tab *Table) hash.Hash32</a></dd>
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<dd><a href="index.html#NewIEEE">func NewIEEE() hash.Hash32</a></dd>
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<dd><a href="index.html#Update">func Update(crc uint32, tab *Table, p []byte) uint32</a></dd>
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<dd><a href="index.html#Table">type Table</a></dd>
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<dd> <a href="index.html#MakeTable">func MakeTable(poly uint32) *Table</a></dd>
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<h4>Examples</h4>
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<dl>
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<dd><a class="exampleLink" href="index.html#example_MakeTable">MakeTable</a></dd>
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<h4>Package files</h4>
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<p>
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<span style="font-size:90%">
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<a href="http://localhost:6060/src/hash/crc32/crc32.go">crc32.go</a>
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<a href="http://localhost:6060/src/hash/crc32/crc32_amd64.go">crc32_amd64.go</a>
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</span>
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<h2 class="toggleButton" title="Click to show Internal Call Graph section">Internal call graph ▹</h2>
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<h2 class="toggleButton" title="Click to hide Internal Call Graph section">Internal call graph ▾</h2>
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<p>
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In the call graph viewer below, each node
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is a function belonging to this package
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and its children are the functions it
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calls—perhaps dynamically.
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The root nodes are the entry points of the
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package: functions that may be called from
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outside the package.
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There may be non-exported or anonymous
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functions among them if they are called
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dynamically from another package.
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</p>
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<p>
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Click a node to visit that function's source code.
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From there you can visit its callers by
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clicking its declaring <code>func</code>
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token.
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Functions may be omitted if they were
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determined to be unreachable in the
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particular programs or tests that were
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analyzed.
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</p>
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<ul style="margin-left: 0.5in" id="callgraph-0" class="treeview"></ul>
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</div>
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</div> <!-- #pkg-callgraph -->
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<h2 id="pkg-constants">Constants</h2>
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<pre>const (
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<span class="comment">// IEEE is by far and away the most common CRC-32 polynomial.</span>
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<span class="comment">// Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, ...</span>
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<span id="IEEE">IEEE</span> = 0xedb88320
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<span class="comment">// Castagnoli's polynomial, used in iSCSI.</span>
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<span class="comment">// Has better error detection characteristics than IEEE.</span>
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<span class="comment">// http://dx.doi.org/10.1109/26.231911</span>
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<span id="Castagnoli">Castagnoli</span> = 0x82f63b78
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<span class="comment">// Koopman's polynomial.</span>
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<span class="comment">// Also has better error detection characteristics than IEEE.</span>
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<span class="comment">// http://dx.doi.org/10.1109/DSN.2002.1028931</span>
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<span id="Koopman">Koopman</span> = 0xeb31d82e
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)</pre>
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<p>
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Predefined polynomials.
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</p>
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<pre>const <span id="Size">Size</span> = 4</pre>
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<p>
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The size of a CRC-32 checksum in bytes.
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</p>
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<h2 id="pkg-variables">Variables</h2>
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<pre>var <span id="IEEETable">IEEETable</span> = makeTable(<a href="index.html#IEEE">IEEE</a>)</pre>
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<p>
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IEEETable is the table for the IEEE polynomial.
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</p>
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<h2 id="Checksum">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=4825:4870#L167">Checksum</a></h2>
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<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>
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<p>
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Checksum returns the CRC-32 checksum of data
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using the polynomial represented by the Table.
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</p>
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<h2 id="ChecksumIEEE">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=4986:5023#L171">ChecksumIEEE</a></h2>
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<pre>func ChecksumIEEE(data []<a href="../../builtin/index.html#byte">byte</a>) <a href="../../builtin/index.html#uint32">uint32</a></pre>
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<p>
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ChecksumIEEE returns the CRC-32 checksum of data
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using the IEEE polynomial.
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</p>
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<h2 id="New">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=3160:3192#L107">New</a></h2>
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<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>
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<p>
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New creates a new hash.Hash32 computing the CRC-32 checksum
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using the polynomial represented by the Table.
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Its Sum method will lay the value out in big-endian byte order.
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</p>
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<h2 id="NewIEEE">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=3385:3411#L112">NewIEEE</a></h2>
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<pre>func NewIEEE() <a href="../index.html">hash</a>.<a href="../index.html#Hash32">Hash32</a></pre>
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<p>
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NewIEEE creates a new hash.Hash32 computing the CRC-32 checksum
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using the IEEE polynomial.
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Its Sum method will lay the value out in big-endian byte order.
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</p>
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<h2 id="Update">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=4236:4288#L143">Update</a></h2>
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<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>
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<p>
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Update returns the result of adding the bytes in p to the crc.
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</p>
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<h2 id="Table">type <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=1266:1288#L31">Table</a></h2>
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<pre>type Table [256]<a href="../../builtin/index.html#uint32">uint32</a></pre>
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<p>
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Table is a 256-word table representing the polynomial for efficient processing.
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</p>
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<h3 id="MakeTable">func <a href="http://localhost:6060/src/hash/crc32/crc32.go?s=2047:2081#L56">MakeTable</a></h3>
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<pre>func MakeTable(poly <a href="../../builtin/index.html#uint32">uint32</a>) *<a href="index.html#Table">Table</a></pre>
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<p>
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MakeTable returns a Table constructed from the specified polynomial.
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The contents of this Table must not be modified.
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</p>
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<div id="example_MakeTable" class="toggle">
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<div class="collapsed">
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<p class="exampleHeading toggleButton">▹ <span class="text">Example</span></p>
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</div>
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<div class="expanded">
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<p class="exampleHeading toggleButton">▾ <span class="text">Example</span></p>
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<p>Code:</p>
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<pre class="code"><span class="comment">// In this package, the CRC polynomial is represented in reversed notation,</span>
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<span class="comment">// or LSB-first representation.</span>
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<span class="comment">//</span>
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<span class="comment">// LSB-first representation is a hexadecimal number with n bits, in which the</span>
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<span class="comment">// most significant bit represents the coefficient of x⁰ and the least significant</span>
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<span class="comment">// bit represents the coefficient of xⁿ⁻¹ (the coefficient for xⁿ is implicit).</span>
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<span class="comment">//</span>
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<span class="comment">// For example, CRC32-Q, as defined by the following polynomial,</span>
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<span class="comment">// x³²+ x³¹+ x²⁴+ x²²+ x¹⁶+ x¹⁴+ x⁸+ x⁷+ x⁵+ x³+ x¹+ x⁰</span>
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<span class="comment">// has the reversed notation 0b11010101100000101000001010000001, so the value</span>
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<span class="comment">// that should be passed to MakeTable is 0xD5828281.</span>
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crc32q := crc32.MakeTable(0xD5828281)
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fmt.Printf("%08x\n", crc32.Checksum([]byte("Hello world"), crc32q))
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<span class="comment"></pre>
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<p>Output:</p>
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<pre class="output">2964d064
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</pre>
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</div>
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</div>
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