PHP 4 >= 4.0.1, PHP 5, PHP 7, PHP 8
crc32 - Calculates the crc32 polynomial of a string

crc32( string$string ): int

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


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).



The data.

Return Values

Returns the crc32 checksum of string as an integer.

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Function crc32:

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