function isbn_check_10 in ISBN Field 6.0

Same name and namespace in other branches

1. 7 isbn.module \isbn_check_10()

2 calls to isbn_check_10()

isbn_build_isbns in ./isbn.module

isbn_form_submit in ./isbn.module

File

./isbn.module, line 145

Maintains a consistant relationship between nodes and ISBNs.

Code

function isbn_check_10($isbn) {
  for ($i = 0; $i < 9; $i++) {
    $digit = substr($isbn, $i, 1);
    $total = $total + $digit * (10 - $i);
  }
  $remainder = $total % 11;
  $check = 11 - $remainder;
  if ($check == 10) {
    $check = 'X';
  }
  elseif ($check == 11) {
    $check = 0;
  }
  return $check;
}