PHP computes a string of 32-bit CRC function CRC32 ()

Instance

Results of output CRC32 ():

<?php$str = CRC32 ("Hello world!"); printf ("%un", $str);? >

Definition and usage

The CRC32 () function computes a 32-bit CRC (cyclic redundancy check) for a string.

This function can be used to verify the integrity of the data.

Tip: To ensure that you can get the correct string representation from the CRC32 () function, you must use the%u format of the printf () or sprintf () function. If you do not use the%u format, the results may appear as incorrect numbers or negative values.

Grammar

CRC32 (String)

Parameter description

string is required. Specifies the string to be computed.

Technical details

Return value: A 32-bit cyclic redundancy check code polynomial that returns a string as an integer.

PHP version: 4.0.1+

Example 1

In this example, we will output the results of the CRC32 () (note the same result) in the case of using and not using the "%u" format character:

<?php$str = CRC32 ("Hello world!"); Echo ' without%u: '. $str. " <br> "; Echo ' with%u: ';p rintf ("%u ", $str);? >

The above code will output:

Without%u:461707669with%u:461707669

Example 2

In this example, we will output the results of CRC32 () without using the "%u" format character (note the result is not the same):

<?php$str = CRC32 ("Hello World"); Echo ' without%u: '. $str. " <br> "; Echo ' with%u: ';p rintf ("%u ", $str);? >

The above code will output:

Without%u: -1959132156with%u:2335835140

The result returned by CRC32 will overflow on a 32-bit machine, so the result may be negative. The 64-bit machine does not overflow, so it is always positive.

The CRC algorithm is calculated by bit-length bits.

The CRC32 function is calculated as a reference to the two constants in PHP Php_int_size,php_int_max
The definitions of these two constants:
The word length of an integer is related to the platform, although the usual maximum value is approximately 2 billion (32-bit signed). PHP does not support unsigned integers. The length of the integer value can be expressed as a constant php_int_size, since PHP 4.4.0 and PHP 5.0.5, the maximum value can be expressed as a constant php_int_max.
Output under 32 bits in php_int_size:4,php_int_max:2147483647
Output under 64 bits in php_int_size:8,php_int_max:9223372036854775807