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  <h1>Package crc32</h1>


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			<dd><code>import "hash/crc32"</code></dd>
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				<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.
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				<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>&nbsp; &nbsp; <a href="index.html#MakeTable">func MakeTable(poly uint32) *Table</a></dd>
				
				
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			<h4>Package files</h4>
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			<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>
			
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			<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&#39;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&#39;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">
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		<p class="exampleHeading toggleButton">▹ <span class="text">Example</span></p>
	</div>
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		<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(&#34;%08x\n&#34;, crc32.Checksum([]byte(&#34;Hello world&#34;), crc32q))
<span class="comment"></pre>
			
			<p>Output:</p>
			<pre class="output">2964d064
</pre>
			
		
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