DECLARE SUB GIF.Info (G AS ANY)
DECLARE SUB GIF.TBI (G AS ANY)
DECLARE FUNCTION GIF.GetBits% (FileNo AS INTEGER, bits AS INTEGER, NextBlock AS INTEGER)

TYPE GIFinfo
  FileNo AS INTEGER
  Ver AS STRING * 3
  Width AS INTEGER
  Height AS INTEGER
  SourcePalette AS INTEGER
  PaletteSize AS INTEGER
  GlobalPaletteFlag AS INTEGER
  Sorted AS INTEGER
  Background AS INTEGER
  Aspect AS INTEGER
END TYPE

TYPE GIFimdesc
  Left AS INTEGER
  Top AS INTEGER
  Width AS INTEGER
  Height AS INTEGER
END TYPE
DIM G AS GIFinfo
G.FileNo = 1
' PATH GOES HERE
OPEN "C:\path\to\gif.gif" FOR BINARY AS G.FileNo
' --------------
GIF.Info G
IF G.GlobalPaletteFlag THEN
  DIM Pal(0 TO G.PaletteSize * 3 - 1) AS STRING * 1
  GIF.GlobalPalette G, Pal()
  SCREEN 12
  ' <------------------------------------>
  ' This section is for use with SCREEN 12
  Dummy% = INP(&H3DA)
  FOR I = 0 TO G.PaletteSize - 1
    OUT &H3C0, I
    OUT &H3C0, I
  NEXT
  OUT &H3C0, 32
  ' <------------------------------------>
  OUT &H3C8, 0
  FOR I = 0 TO G.PaletteSize - 1
    OUT &H3C9, ASC(Pal(I * 3))
    OUT &H3C9, ASC(Pal(I * 3 + 1))
    OUT &H3C9, ASC(Pal(I * 3 + 2))
  NEXT
END IF
DIM byte AS STRING * 1
DO
  IF EOF(1) THEN EXIT DO
  GET G.FileNo, , byte
  SELECT CASE byte
  CASE ","
    GIF.TBI G
  CASE "!"
    GET G.FileNo, , byte
    IF ASC(byte) = &HF9 THEN
      FOR I = 0 TO 5
        GET G.FileNo, , byte
      NEXT
    ELSE
      PRINT "Unknown extension: 0x" + HEX$(ASC(byte))
    END IF
  CASE ";"
    'END OF GIF
    EXIT DO
  CASE ELSE
    PRINT "Unknown magic byte: 0x" + HEX$(ASC(byte))
  END SELECT
LOOP
CLOSE

SUB GIF.GlobalPalette (G AS GIFinfo, Pal() AS STRING * 1)
DIM I AS INTEGER
FOR I = 0 TO G.PaletteSize * 3 - 1
  GET G.FileNo, , Pal(I)
  Pal(I) = CHR$(ASC(Pal(I)) \ 4)
NEXT
END SUB

FUNCTION GIF.GetBits% (FileNo AS INTEGER, bits AS INTEGER, NextBlock AS INTEGER)
STATIC position AS INTEGER, byte AS STRING * 1
IF bits = 0 THEN GET FileNo, , byte: EXIT FUNCTION
DIM I AS INTEGER, X AS INTEGER
X = 2 ^ (position)
I = ASC(byte) \ X
X = 2 ^ (8 - position)
position = position + bits
IF position >= 8 THEN
  DO
    GET FileNo, , byte
    IF LOC(FileNo) = NextBlock THEN
      NextBlock = NextBlock + 1 + ASC(byte)
      IF ASC(byte) = 0 THEN
        PRINT "Bad format!"
        SYSTEM
      END IF
      GET FileNo, , byte
    END IF
    position = position - 8
    I = I OR ((ASC(byte) AND (2 ^ position - 1)) * X)
    IF position < 8 THEN EXIT DO
    X = X * 256
  LOOP
END IF
I = I AND (2 ^ bits - 1)
GIF.GetBits = I
END FUNCTION

SUB GIF.Info (G AS GIFinfo)
DIM byte AS STRING * 1
GET G.FileNo, , G.Ver
IF G.Ver <> "GIF" THEN
  PRINT "Magic Number Wrong! Press Enter to continue or anything else to exit."
  DO
    K$ = INKEY$
  LOOP UNTIL LEN(K$)
  IF K$ <> CHR$(13) THEN SYSTEM
END IF
GET G.FileNo, , G.Ver
GET G.FileNo, , G.Width
GET G.FileNo, , G.Height
GET G.FileNo, , byte
IF ASC(byte) AND 128 THEN G.GlobalPaletteFlag = -1 ELSE G.GlobalPaletteFlag = 0
G.SourcePalette = 2 ^ (((ASC(byte) AND 64 + 32 + 16) \ 16) + 1)
G.PaletteSize = 2 ^ ((ASC(byte) AND 7) + 1)
G.Sorted = ASC(byte) AND 8
GET G.FileNo, , byte
G.Background = ASC(byte)
GET G.FileNo, , byte
G.Aspect = ASC(byte)
END SUB

SUB GIF.TBI (G AS GIFinfo)
DIM M AS GIFimdesc, byte AS STRING * 1
DIM I AS INTEGER
GET G.FileNo, , M
GET G.FileNo, , byte
DIM LocalPaletteFlag AS INTEGER, InterlaceFlag AS INTEGER, SortFlag AS INTEGER, LocalPaletteSize AS INTEGER
IF ASC(byte) AND 128 THEN LocalPaletteFlag = -1
IF ASC(byte) AND 64 THEN InterlaceFlag = -1: PRINT "INTERLACED!!!!!!!!!!!!!!": STOP
IF ASC(byte) AND 32 THEN SortFlag = -1
LocalPaletteSize = 2 ^ ((ASC(byte) AND 7) + 1)
IF LocalPaletteFlag THEN
  OUT &H3C8, 0
  FOR I = 0 TO LocalPaletteSize * 3 - 1
    GET G.FileNo, , byte
    OUT &H3C9, ASC(byte) \ 4
  NEXT
END IF
DIM X AS INTEGER, Y AS INTEGER
DIM MinCodeSize AS INTEGER
GET G.FileNo, , byte
MinCodeSize = ASC(byte)
DIM Dic((2 ^ MinCodeSize) + 2 TO 4095) AS STRING
DIM CCS AS INTEGER, DS AS INTEGER, RS AS INTEGER, US AS INTEGER
DIM K AS INTEGER, W AS STRING, E AS STRING
CCS = MinCodeSize + 1
US = 2 ^ MinCodeSize - 1
RS = US + 2
DS = RS
DIM FileOffset AS INTEGER
GET G.FileNo, , byte
FileOffset = LOC(G.FileNo) + 1 + ASC(byte)
Dummy = GIF.GetBits(G.FileNo, 0, 0)
X = 0: Y = 0
E = ""
W = ""
DO
  K = GIF.GetBits(G.FileNo, CCS, FileOffset)
  IF K <= US THEN
    E = CHR$(K)
  ELSEIF K > RS THEN
    IF K <= DS THEN
      E = Dic(K)
    ELSE
      E = W + LEFT$(W, 1)
    END IF
  ELSEIF K = RS - 1 THEN
    DS = RS
    CCS = MinCodeSize + 1
    E = ""
    W = ""
  ELSEIF K = RS THEN
    'PRINT "End of file stream"
    EXIT SUB
  END IF
  FOR I = 1 TO LEN(E)
    PSET (X, Y), ASC(MID$(E, I, 1))
    X = X + 1
    IF X >= M.Width THEN X = 0: Y = Y + 1
  NEXT
  IF LEN(W) THEN
    IF DS < 4095 THEN
      DS = DS + 1
      IF DS >= 2 ^ CCS - 1 THEN CCS = CCS + 1
      Dic(DS) = W + LEFT$(E, 1)
    END IF
  END IF
  W = E
LOOP
END SUB