- abs: documentation ( source)
- str_split: documentation ( source)
<?php
function GetLuhnCheckDigit($number) {
$sum = 0;
$alt = true;
$digits = str_split($number);
for ($i = count($digits) - 1; $i >= 0; $i--) {
$curDigit = $digits[$i];
if ($alt) {
$curDigit *= 2;
if ($curDigit > 9)
$curDigit -= 9;
}
$sum += $curDigit;
$alt = false;
}
if (($sum % 10) == 0 ){
return 0;
}
echo abs($sum) . PHP_EOL;
return (10 - (abs($sum) % 10));
}
echo GetLuhnCheckDigit(12345678912345678918);