Category : BASIC Source Code
Archive   : HUFFMAN2.ZIP
Filename : DECODER.BAS

 
Output of file : DECODER.BAS contained in archive : HUFFMAN2.ZIP
'Huffman decoder
'by Rich Geldreich May 29th, 1992
'This program is in the public domain.
DEFINT A-Z

DECLARE FUNCTION GetBit ()
DECLARE SUB FillBuff ()

CONST True = -1, False = 0
CONST Null = -2
CONST BufferLength = 10000

DIM SHARED Bits(8)
DIM SHARED Father(512)
DIM SHARED LeftSon(512)
DIM SHARED RightSon(512)

DIM SHARED Buffer$, Address, EndAddress, CurrentByte, BitsIn, BufferSeg

Bits:
DATA 1,2,4,8,16,32,64,128,256

RESTORE Bits
FOR A = 0 TO 8: READ Bits(A): NEXT
'disk buffer
Buffer$ = STRING$(BufferLength, 0): EndAddress = 1: Address = 0: BitsIn = -1
'turn on cursor
LOCATE , , 1
'open the compressed file
OPEN "output.huf" FOR BINARY AS #1
'get the header
GET #1, , FileLength&
GET #1, , RealIndex
GET #1, , TopOfTree
'read in the tree
FOR A = 0 TO RealIndex
IF GetBit THEN
Father = 0
FOR C = 0 TO 7
IF GetBit THEN Father = Father + Bits(C)
NEXT
Father(A) = Father
RightSon(A) = Null
LeftSon(A) = Null
ELSE
Father(A) = 256
IF GetBit THEN
Son = 0
FOR C = 0 TO 8
IF GetBit THEN Son = Son + Bits(C)
NEXT
LeftSon(A) = Son
ELSE
LeftSon(A) = Null
END IF
IF GetBit THEN
Son = 0
FOR C = 0 TO 8
IF GetBit THEN Son = Son + Bits(C)
NEXT
RightSon(A) = Son
ELSE
RightSon(A) = Null
END IF
END IF
NEXT
'when PrintCounter=1024 then screen is updated
PrintCounter = 0
'A$ is the output buffer
A$ = STRING$(5000, 0)
A& = SADD(A$)
A& = A& - 65536 * (A& < 0)
OutputSeg = VARSEG(A$) + (A& \ 16)
OAddress = (A& MOD 16)
OEndAddress = OAddress + 5000
OStart = OAddress
'start decoding
PRINT "Decoding:";
Xpos = POS(0): Ypos = CSRLIN
'open output file
OPEN COMMAND$ FOR BINARY AS #2
'decode each byte
FOR CurrentByte& = 1 TO FileLength&
DEF SEG = BufferSeg
'start at top of tree
A = TopOfTree
'keep on getting bits until a character is found
DO
'if BitsIn<0 then time to fill byte buffer
IF BitsIn < 0 THEN
Address = Address + 1
'if Address=EndBuffer then time to fill disk buffer
IF Address = EndAddress THEN
FillBuff
END IF
CurrentByte = PEEK(Address): BitsIn = 7
END IF
'see if we go left or right
IF (CurrentByte AND Bits(BitsIn)) THEN A = LeftSon(A) ELSE A = RightSon(A)
BitsIn = BitsIn - 1
F = Father(A)
'loop until an ascii character is found
LOOP UNTIL F < 256
'put byte into output buffer
DEF SEG = OutputSeg
POKE OAddress, F
OAddress = OAddress + 1
IF OAddress = OEndAddress THEN
PUT #2, , A$
A& = SADD(A$)
A& = A& - 65536 * (A& < 0)
OutputSeg = VARSEG(A$) + (A& \ 16)
OAddress = (A& MOD 16)
OEndAddress = OAddress + 5000
OStart = OAddress
END IF
'see if time to update the screen
PrintCounter = PrintCounter + 1
IF PrintCounter = 1024 THEN
PrintCounter = 0
LOCATE Ypos, Xpos
PRINT (CurrentByte& * 100) \ FileLength&; "%";
END IF
'loop until all of the characters have been restored
NEXT
'save whatever is currently in the output buffer
A$ = LEFT$(A$, OAddress - OStart)
PUT #2, , A$
CLOSE
'all done
LOCATE Ypos, Xpos
PRINT " done."

END

'fills the input buffer
SUB FillBuff
GET #1, , Buffer$
A& = SADD(Buffer$)
A& = A& - 65536 * (A& < 0)
BufferSeg = VARSEG(Buffer$) + (A& \ 16)
Address = (A& MOD 16)
EndAddress = Address + BufferLength
DEF SEG = BufferSeg
END SUB

'gets one bit from the input file(only used when the tree
'is read in)
FUNCTION GetBit STATIC
IF BitsIn < 0 THEN
Address = Address + 1
IF Address = EndAddress THEN
FillBuff
END IF
CurrentByte = PEEK(Address): BitsIn = 7
END IF
GetBit = (CurrentByte AND Bits(BitsIn)): BitsIn = BitsIn - 1
END FUNCTION



  3 Responses to “Category : BASIC Source Code
Archive   : HUFFMAN2.ZIP
Filename : DECODER.BAS

  1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

  2. This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

  3. But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/