private function ISBNtest::get_isbn10_checkdigit in Biblio Advanced Import 7

Same name and namespace in other branches

1. 6 lib/isbntest.class.php \ISBNtest::get_isbn10_checkdigit()

2 calls to ISBNtest::get_isbn10_checkdigit()

ISBNtest::get_isbn10 in lib/isbntest.class.php

ISBNtest::valid_isbn10 in lib/isbntest.class.php

File

lib/isbntest.class.php, line 21

Class

ISBNtest

Code

private function get_isbn10_checkdigit() {
  if (strlen($this->isbn10) != 10) {
    return FALSE;
    $this->error = "Given ISBN-10 is not 10 digits (" . $this->isbn10 . ")";
  }

  /*
   * this checkdigit calculation could probably be expressed in less
   * space using a lop, but this keeps it very clear what the math
   * involved is
   */
  $checkdigit = 11 - (10 * substr($this->isbn10, 0, 1) + 9 * substr($this->isbn10, 1, 1) + 8 * substr($this->isbn10, 2, 1) + 7 * substr($this->isbn10, 3, 1) + 6 * substr($this->isbn10, 4, 1) + 5 * substr($this->isbn10, 5, 1) + 4 * substr($this->isbn10, 6, 1) + 3 * substr($this->isbn10, 7, 1) + 2 * substr($this->isbn10, 8, 1)) % 11;

  /*
   * convert the numeric check value
   * into the single char version
   */
  switch ($checkdigit) {
    case 10:
      $checkdigit = "X";
      break;
    case 11:
      $checkdigit = 0;
      break;
    default:
  }
  return $checkdigit;
}