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https://github.com/sigmasternchen/php-doc-en
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e095023e40
Partial merge of https://github.com/php/doc-en/pull/265. git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@351904 c90b9560-bf6c-de11-be94-00142212c4b1
135 lines
4.1 KiB
XML
135 lines
4.1 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<refentry xmlns="http://docbook.org/ns/docbook" xml:id="function.crc32">
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<refnamediv>
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<refname>crc32</refname>
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<refpurpose>Calculates the crc32 polynomial of a string</refpurpose>
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</refnamediv>
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<refsect1 role="description">
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&reftitle.description;
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<methodsynopsis>
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<type>int</type><methodname>crc32</methodname>
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<methodparam><type>string</type><parameter>string</parameter></methodparam>
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</methodsynopsis>
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<para>
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Generates the cyclic redundancy checksum polynomial of 32-bit
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lengths of the <parameter>string</parameter>. This is usually used
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to validate the integrity of data being transmitted.
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</para>
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<warning>
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<simpara>
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Because PHP's integer type is signed many crc32 checksums will
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result in negative integers on 32bit platforms. On 64bit installations
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all <function>crc32</function> results will be positive integers though.
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</simpara>
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<simpara>
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So you need to use the "%u" formatter of <function>sprintf</function> or
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<function>printf</function> to get the string representation of the
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unsigned <function>crc32</function> checksum in decimal format.
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</simpara>
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<simpara>
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For a hexadecimal representation of the checksum you can either use the
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"%x" formatter of <function>sprintf</function> or <function>printf</function>
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or the <function>dechex</function> conversion functions, both of these
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also take care of converting the <function>crc32</function> result to
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an unsigned integer.
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</simpara>
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<simpara>
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Having 64bit installations also return negative integers for higher
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result values was considered but would break the hexadecimal conversion
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as negatives would get an extra 0xFFFFFFFF######## offset then. As
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hexadecimal representation seems to be the most common use case we
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decided to not break this even if it breaks direct decimal comparisons
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in about 50% of the cases when moving from 32 to 64bits.
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</simpara>
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<simpara>
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In retrospect having the function return an integer maybe wasn't the
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best idea and returning a hex string representation right away (as
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e.g. <function>md5</function> does) might have been a better plan to
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begin with.
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</simpara>
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<simpara>
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For a more portable solution you may also consider the generic
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<function>hash</function>. <code>hash("crc32b", $str)</code> will
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return the same string as <code>str_pad(dechex(crc32($str)), 8, '0', STR_PAD_LEFT)</code>.
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</simpara>
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</warning>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>string</parameter></term>
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<listitem>
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<para>
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The data.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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Returns the crc32 checksum of <parameter>string</parameter> as an integer.
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</para>
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</refsect1>
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<refsect1 role="examples">
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&reftitle.examples;
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<para>
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<example>
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<title>Displaying a crc32 checksum</title>
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<para>
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This example shows how to print a converted checksum with the
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<function>printf</function> function:
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</para>
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<programlisting role="php">
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<![CDATA[
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<?php
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$checksum = crc32("The quick brown fox jumped over the lazy dog.");
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printf("%u\n", $checksum);
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?>
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]]>
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</programlisting>
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</example>
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</para>
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member><function>hash</function></member>
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<member><function>md5</function></member>
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<member><function>sha1</function></member>
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</simplelist>
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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