Procedure to convert Roman to Arabic

CREATE OR ALTER PROCEDURE PRO_ROMANOS_TO_ARABICOS (
    ANUMERAL VARCHAR(100),
    ADEFAULT INTEGER)
RETURNS (
    RESULT INTEGER)
AS
  DECLARE VARIABLE I INTEGER;
  DECLARE VARIABLE C CHAR(1);
  DECLARE VARIABLE N CHAR(1);
  DECLARE VARIABLE VC INTEGER;
  DECLARE VARIABLE VN INTEGER;
  DECLARE VARIABLE TOTAL INTEGER;
BEGIN
  RESULT   = :ADEFAULT;
  I        = 1;
  TOTAL    = 0;
  ANUMERAL = UPPER(:ANUMERAL);

  WHILE (I <= CHARACTER_LENGTH(:ANUMERAL)) DO
  BEGIN
    C = SUBSTRING(:ANUMERAL FROM :I FOR 1);

    IF (:C NOT IN ('I', 'V', 'X', 'L', 'C', 'D', 'M')) THEN
    BEGIN
      SUSPEND;
      EXIT;
    END

    I = I + 1;
  END

  I = CHARACTER_LENGTH(:ANUMERAL);
  WHILE (I > 0) DO
  BEGIN
    N  = '';
    C  = SUBSTRING(:ANUMERAL FROM CHARACTER_LENGTH(:ANUMERAL) FOR 1);
    VC = 0;
    VN = 0;

    IF (CHARACTER_LENGTH(:ANUMERAL) > 1) THEN
      N = SUBSTRING(:ANUMERAL FROM CHARACTER_LENGTH(:ANUMERAL)-1 FOR 1);

    IF (:C = 'I') THEN
      VC = 1;
    ELSE
    IF (:C = 'V') THEN
      VC = 5;
    ELSE
    IF (:C = 'X') THEN
      VC = 10;
    ELSE
    IF (:C = 'L') THEN
      VC = 50;
    ELSE
    IF (:C = 'C') THEN
      VC = 100;
    ELSE
    IF (:C = 'D') THEN
      VC = 500;
    ELSE
    IF (:C = 'M') THEN
      VC = 1000;

     IF (:N = 'I') THEN
      VN = 1;
    ELSE
    IF (:N = 'V') THEN
      VN = 5;
    ELSE
    IF (:N = 'X') THEN
      VN = 10;
    ELSE
    IF (:N = 'L') THEN
      VN = 50;
    ELSE
    IF (:N = 'C') THEN
      VN = 100;
    ELSE
    IF (:N = 'D') THEN
      VN = 500;
    ELSE
    IF (:N = 'M') THEN
      VN = 1000;

    IF (:VN < :VC) THEN
    BEGIN
      TOTAL = :TOTAL + (:VC - :VN);

      IF (:VN = 0) THEN
      BEGIN
        RESULT = :TOTAL;
        SUSPEND;
        EXIT;
      END

      ANUMERAL = SUBSTRING(:ANUMERAL FROM 1 FOR CHARACTER_LENGTH(:ANUMERAL)-2);
      I        = I - 2;
    END
    ELSE
    BEGIN
      TOTAL    = :TOTAL + :VC;
      ANUMERAL = SUBSTRING(:ANUMERAL FROM 1 FOR CHARACTER_LENGTH(:ANUMERAL)-1);
      I        = I - 1;
    END
  END

  RESULT = :TOTAL;
  SUSPEND;
END