function isbn_check_13 in ISBN Field 6.0

Same name and namespace in other branches

1. 7 isbn.module \isbn_check_13()

2 calls to isbn_check_13()

isbn_build_isbns in ./isbn.module

isbn_form_submit in ./isbn.module

File

./isbn.module, line 161

Maintains a consistant relationship between nodes and ISBNs.

Code

function isbn_check_13($isbn) {
  $weight = 1;
  for ($i = 0; $i < 12; $i++) {
    $digit = substr($isbn, $i, 1);
    $total = $total + $digit * $weight;

    //drupal_set_message(' i '.$i.' digit '.$digit.' x '.$weight.'Total '.$total);
    if ($weight == 1) {
      $weight = 3;
    }
    else {
      $weight = 1;
    }
  }
  $remainder = $total % 10;
  $check = 10 - $remainder;
  if ($check == 10) {
    $check = '0';
  }
  return $check;
}