BYTE FUNC FindIndex(BYTE b)
  IF b>='A AND b<='Z THEN
    RETURN (b-'A)
  ELSEIF b>='a AND b<='z THEN
    RETURN (b-'a+26)
  ELSEIF b>='0 AND b<='9 THEN
    RETURN (b-'0+52)
  ELSEIF b='+ THEN
    RETURN (62)
  ELSEIF b='/ THEN
    RETURN (63)
  FI
RETURN (-1)

PROC PrintChar(CHAR c)
  IF c=10 THEN
    PutE()
  ELSE
    Put(c)
  FI
RETURN

PROC Decode(CHAR ARRAY s)
  BYTE i,b1,b2,b3,b4,i1,i2,i3,i4
  CHAR c

  IF s(0) MOD 4#0 THEN
    PrintE("Invalid length of string!!!")
    Break()
  FI

  i=1
  WHILE i<=s(0)
  DO
    b1=s(i) i==+1
    b2=s(i) i==+1
    b3=s(i) i==+1
    b4=s(i) i==+1

    i1=FindIndex(b1)
    i2=FindIndex(b2)

    c=i1 LSH 2
    c==%i2 RSH 4
    PrintChar(c)

    IF b3#'= THEN
      i3=FindIndex(b3)
      c=(i2&$0F) LSH 4
      c==%i3 RSH 2
      PrintChar(c)

      IF b4#'= THEN
        i4=FindIndex(b4)
        c=(i3&$03) LSH 6
        c==%i4
        PrintChar(c)
      FI
    FI
  OD
RETURN

PROC Test(CHAR ARRAY s)
  PrintE("Encoded:")
  PrintE(s)
  PutE()
  PrintE("Decoded:")
  Decode(s)
  PutE()
RETURN

PROC Main()
  Test("VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY29tcHV0ZXIuCiAgICAtLVBhdWwgUi5FaHJsaWNo")
RETURN