Algo Luhn

library/Metier/Util/Luhn.php

@@ -0,0 +1,49 @@
+<?php
+class Metier_Util_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(string $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);
+    }
+
+    /**
+     * Validate number against check digit
+     *
+     * @param string $number
+     * @param integer $digit
+     * @return boolean
+     */
+    public function validate(string $number, int $digit)
+    {
+        $calculated = $this->calculate($number);
+        if($digit == $calculated) {
+            return true;
+        }
+        else {
+            return false;
+        }
+    }
+}