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crc32

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(PHP 4 >= 4.0.1, PHP 5, PHP 7)

crc32 — Calculates the crc32 polynomial of a string

Description

crc32 ( string $str ) : int

Generates the cyclic redundancy checksum polynomial of 32-bit lengths of the str. This is usually used to validate the integrity of data being transmitted.

Warning

Because PHP's integer type is signed many crc32 checksums will result in negative integers on 32bit platforms. On 64bit installations all crc32() results will be positive integers though.

So you need to use the "%u" formatter of sprintf() or printf() to get the string representation of the unsigned crc32() checksum in decimal format.

For a hexadecimal representation of the checksum you can either use the "%x" formatter of sprintf() or printf() or the dechex() conversion functions, both of these also take care of converting the crc32() result to an unsigned integer.

Having 64bit installations also return negative integers for higher result values was considered but would break the hexadecimal conversion as negatives would get an extra 0xFFFFFFFF######## offset then. As hexadecimal representation seems to be the most common use case we decided to not break this even if it breaks direct decimal comparisons in about 50% of the cases when moving from 32 to 64bits.

In retrospect having the function return an integer maybe wasn't the best idea and returning a hex string representation right away (as e.g. md5() does) might have been a better plan to begin with.

For a more portable solution you may also consider the generic hash(). hash("crc32b", $str) will return the same string as str_pad(dechex(crc32($str)), 8, '0', STR_PAD_LEFT).

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Return Values

Returns the crc32 checksum of str as an integer.

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Examples

Example #1 Displaying a crc32 checksum

This example shows how to print a converted checksum with the printf() function:

<?php
$checksum = crc32("The quick brown fox jumped over the lazy dog.");
printf("%u\n", $checksum);
?>

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See Also

  • hash() - Generate a hash value (message digest)
  • md5() - Calculate the md5 hash of a string
  • sha1() - Calculate the sha1 hash of a string

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Document created the 30/01/2003, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/php-rf-crc32.html

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References

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