PHP ISBN Functions

A while back, when the ISBN-13 standard was released, I wrote some ISBN functions for a project I was working on. Since several people have been looking for such functions, I decided to share the code I wrote. Here is the ISBN class:

<?php

class ISBN {

# Converts an ISBN-10 to ISBN-13.
  # For more information about ISBN-10 to ISBN-13 conversion see:
  # http://www.bisg.org/isbn-13/conversions.html
  #
  public function isbn_10_to_isbn_13( $isbn_10 ) {

  if( !$this->is_valid_isbn_10($isbn_10) ) {
     return false;
  }

  $isbn_13= '978' . $isbn_10;
  $sum=0;
  for( $i= 13; $i > 1; $i-- ) {

     $sum+=  ((int)$isbn_13{13 - $i}) * ((($i % 2) == 0) ? 3 : 1);
  }

  $isbn_13{12}= (($sum % 10) == 0) ? 0 : (10 - ($sum % 10));
  return $isbn_13;
}


# Removes any "white spaces" and hyphens from an ISBN-10 string.
  # Because of the possibility of 'x' or 'X' in ISBN, you should not use the "\D" option.
  #
  public function clean_isbn_10( $str ) {

  $pattern = '/[\s|-]/';
  $replacement = '';
  return preg_replace( $pattern, $replacement, $str );
}


# Validates an ISBN-10 number using the check digit.
  # Use clean_isbn_10 function on the ISBN-10 string before calling this function.
  # For more information see about ISBN-10 numbers see:
  # http://www.isbn.org/standards/home/isbn/international/html/usm4.htm
  #
  public function is_valid_isbn_10( $isbn_10 ) {

  # Note, isbn-10 has 'X' or 'x' as a check digit signifying the number 10
    if( !ereg('^([0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9xX])$', $isbn_10) ) {

    return false;
  }

  $sum= 0;
  for( $i= 10; $i > 1; $i-- ) {

    $sum+= ((int)$isbn_10{10 - $i}) * $i;
  }

  $sum+= ereg('[xX]$', $isbn_10) ? 10 : ( (int)$isbn_10{9} );
  return ( ($sum % 11) == 0 );
}


# Removes any non-numeric characters from an ISBN-13/EAN string.
  #
  public function clean_isbn_13( $str ) {

  $pattern = '/\D/';
  $replacement = '';
  return preg_replace( $pattern, $replacement, $str );
}


# Validates an EAN number using the check digit. Note ISBN-13 numbers are a subset of EAN numbers.
  # For more information about ISBN-13 see:
  # http://www.bisg.org/isbn-13/conversions.html
  #
  public function is_valid_isbn_13( $isbn_13 ) {

 # If you want to strictly validate ISBN-13 numbers substitute this line of code in the IF statement:
 
 # !ereg('^((978|979)[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9])$', $isbn_13)
 
 if( !ereg('^([0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9])$', $isbn_13) ) {

     return false;
  }

  $sum= 0;
  for( $i= 13; $i > 0; $i-- ) {

    $sum+=  ((int)$isbn_13{13 - $i}) * ((($i % 2) == 0) ? 3 : 1);
  }

  return ( ($sum % 10) == 0 );
}
}
?>

Regards,
drenintell