php man page for crc32

CRC32(3)								 1								  CRC32(3)

crc32 - Calculates the crc32 polynomial of a string

SYNOPSIS
       int crc32 (string  $str)

DESCRIPTION
	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  installa-
	      tions all crc32(3) results will be positive integers though.

	       So you need to use the "%u" formatter of sprintf(3) or printf(3) to get the string representation of the unsigned crc32(3) checksum
	      in decimal format.

	       For a hexadecimal representation of the checksum you can either use the "%x" formatter of sprintf(3) or printf(3) or the  dechex(3)
	      conversion functions, both of these also take care of converting the crc32(3) 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(3) does) might have been a better plan to begin with.

	       For  a  more  portable  solution  you  may  also  consider the generic hash(3). hash("crc32b", $str) will return the same string as
	      dechex(crc32($str)).

PARAMETERS
	      o $str
		- The data.

RETURN VALUES
	Returns the crc32 checksum of $str as an integer.

EXAMPLES
       Example #1

	      Displaying a crc32 checksum

	       This example shows how to print a converted checksum with the printf(3) function:

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

SEE ALSO
       hash(3), md5(3), sha1(3).

PHP Documentation Group 														  CRC32(3)