Oracle PL/SQL: ISBN10 Validator

Another little function to make sure you've got a valid ISBN10 before you attempt to convert it.

create or replace
FUNCTION "VALIDATE_ISBN10" (
  ISBN10 IN VARCHAR2
  ) RETURN NUMBER IS

  v_checksum NUMBER := 0;
  v_digit NUMBER := 0; 
  v_pos NUMBER := 1;  
  v_rem NUMBER;

  BEGIN
    IF (LENGTH(ISBN10) != 10)
      THEN RETURN 0;
    END IF;

    WHILE (v_pos <= 9) LOOP
      v_digit := substr(ISBN10,(v_pos),1);
      v_checksum := v_checksum + (v_pos * v_digit);
      v_pos := v_pos + 1;
    END LOOP;
    v_rem := mod(v_checksum,11);
    
    IF (v_rem = 10 AND 'X' = substr(ISBN10,10,1))
      THEN RETURN 1;
    END IF;

    IF (v_rem < 10 AND TO_NUMBER(substr(ISBN10,10,1)) = v_rem)
      THEN RETURN 1;
    END IF;

    return 0;
  exception when value_error then
    return 0;
END VALIDATE_ISBN10;