<?php
/**
* Luhn algorithm (a.k.a. modulus 10) is a simple formula used to validate variety of identification numbers.
* It is not intended to be a cyrptographically secure hash function, it was designed to protect against accidental errors.
* See http://en.wikipedia.org/wiki/Luhn_algorithm
*
* @author Rolands Kusiņš
* @version 0.2
* @license GPL
*/
class Luhn {
private $sumTable = array(array(0, 1, 2, 3, 4, 5, 6, 7, 8, 9), array(0, 2, 4, 6, 8, 1, 3, 5, 7, 9));
/**
* Calculate check digit according to Luhn's algorithm
* New method (suggested by H.Johnson), see http://www.phpclasses.org/discuss/package/8471/thread/1/
*
* @param string $number
* @return integer
*/
public function calculate($number)
{
$length = strlen($number);
$sum = 0;
$flip = 1;
// Sum digits (last one is check digit, which is not in parameter)
for($i = $length-1; $i >= 0; --$i) $sum += $this->sumTable[$flip++ & 0x1][$number[$i]];
// Multiply by 9
$sum *= 9;
// Last digit of sum is check digit
return (int)substr($sum, -1, 1);
}
/**
* Calculate check digit according to Luhn's algorithm
* This is an old method, tests show that this is little bit slower than new one
*
* @param string $number
* @return integer
*/
public function calculateOld($number) {
$length = strlen($number);
$sum = 0;
$p = $length % 2;
// Sum digits, where every second digit from right is doubled (last one is check digit, which is not in parameter)
for($i = $length-1; $i >= 0; --$i) {
$digit = $number[$i];
// Every second digit is doubled
if ($i % 2 != $p) {
$digit *= 2;
// If doubled value is 10 or more (for example 13), then add to sum each digit (i.e. 1 and 3)
if($digit > 9){
$sum += $digit[0];
$sum += $digit[1];
} else{
$sum += $digit;
}
} else{
$sum += $digit;
}
}
// Multiply by 9
$sum *= 9;
// Last one is check digit
return (int)substr($sum, -1, 1);
}
/**
* Validate number against check digit
*
* @param string $number
* @param integer $digit
* @return boolean
*/
public function validate($number,$digit){
$calculated = $this->calculate($number);
if($digit == $calculated) return true;
else return false;
}
}
?>
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