'===========================================================================
' Subject: PB HUFFMAN ENCODER                Date: 12-03-93 (15:30)       
' Author:  M. Rosenberg                      Code: PB                     
' Origin:  QBTIPS_T.DOC                    Packet: ALGOR.ABC
'===========================================================================
'Hey all, well I a recently got a Hufman algrorithm for BASIC. Sadly it
'was made only for PowerBasic and I use QuickBasic.  Could some of you
'guys out there with both QB/PB experience possibly modify the code ??

CLS
InFile$="A SIMPLE STRING TO BE ENCODED USING A MINIMAL NUMBER OF BITS"

CALL Huffman(InFile$,OutFile$,NewFile$)
print:print:print
PRINT "In:  ";LEN(InFile$);InFile$
PRINT "Out: ";LEN(OutFile$)
PRINT "New: ";LEN(NewFile$);NewFile$
input,r

END
'**********************************************************************
'   Huffman Encoding File Compression Technique
'
'   From: R Sedgwick.  Algorithms.  Reading, MA: Addison-Wesley.
'                      1984.  Second Ed.  pp  286 / 93.
'
'   Converted to Power Basic by M. Rosenberg CI$: [73707,2545]
'
SUB Huffman(InText$,OutText$,NewText$)
    SHARED N%,Heap%(),Count%()
    DIM Count%(1024),Heap%(1024),Dad%(1024),Code%(256),Leng%(256)

' Count the frequency of each character in the message to be encoded (P. 287)
    FOR I%=0 to 255 : Count%(I%)=0 : NEXT I%
    Csr%=0
    DO : INCR Csr% : X%=ASC(MID$(InText$,Csr%,1)) : INCR Count%(X%)
         LOOP UNTIL Csr%=LEN(InText$)

' Initialize the heap array to point to non-zero frequency counts (P. 290)

    N%=0 : FOR I%=0 to 255 : IF Count%(I%)<>0 THEN INCR N% : Heap%(N%)=I%
           NEXT I%
' Construct an indirect heap on the frequency values (P. 289)

    FOR K% = N% TO 1 STEP -1 : CALL PqDownHeap(K%) : NEXT K%

' Construct the trie (P. 290)
    DO : T%=Heap%(1) : Heap%(1)=Heap%(N%) : DECR N%
             CALL PqDownHeap(1)
             Count%(255+N%)=Count%(Heap%(1))+Count%(T%)
             Dad%(T%)=255+N% : Dad%(Heap%(1))=-255-N%
             Heap%(1)=255+N% : CALL PqDownHeap(1)
    LOOP UNTIL N%=1
    Dad%(255+N%)=0

' Reconstruct the information from the representation of the coding tree (P.291)
'    computed during the sifting process.

    FOR K% = 0 TO 255
        IF Count%(K%)=0 THEN
           Code%(K%)=0 : Leng%(K%)=0
        ELSE
           I%=0 : J&=1 : T%=Dad%(K%) : X%=0
           DO : IF T%<0 THEN X%=X%+J& : T%=0-T%
                T%=Dad%(T%) : J&=J&+J& : INCR I%
           LOOP UNTIL T%=0
           Code%(K%)=X% : Leng%(K%)=I%
        END IF
    NEXT K%
' Use the computed representations of the code to encode the string (P. 292)

    J%=0 : OutText$="" : Hold$=""
    DO : INCR J%
             Char%=ASC(MID$(InText$,J%,1)) : Compr$=BIN$(Code%(Char%))
             DO WHILE LEN(Compr$)< Leng%(Char%) : Compr$="0"+Compr$ : LOOP
             Hold$=Hold$+Compr$
             IF LEN(Hold$)>8 THEN
                          
                OutText$=OutText$+CHR$(Bin2Int(LEFT$(Hold$,8))) Hold$=RIGHT$(Hold$,LEN(Hold$)-8)
             END IF
    LOOP UNTIL J%=LEN(InText$)

' Add a byte at the end that contains any left-over bits

    IF LEN(Hold$)>0 THEN
             Hold$=Hold$+STRING$(8-LEN(Hold$),"0")
             OutText$=OutText$+CHR$(Bin2Int(LEFT$(Hold$,8)))
    END IF
'**********************************************************************
' Unpack compressed string into character representation of binary

    J%=0 : UnCompr$="" : NewText$=""
    DO : INCR J%
         Hold$=MID$(OutText$,J%,1) : Hold$=BIN$(ASC(Hold$))
         DO WHILE LEN(Hold$)<8 : Hold$="0"+Hold$ : LOOP
         UnCompr$=UnCompr$+Hold$
    LOOP UNTIL J%=LEN(OutText$)

' Decode compressed string

    DO : FOR  K%=1 TO 256
         IF K%=256 THEN EXIT LOOP 'All done
         IF Leng%(K%)>0 THEN
            IF Bin2Int(LEFT$(UnCompr$,Leng%(K%)))=Code%(K%) THEN
                                                                     
               UnCompr$=RIGHT$(UnCompr$,LEN(UnCompr$)-Leng%(K%))
               NewText$=NewText$+CHR$(K%) : EXIT FOR
            END IF
        END IF
        NEXT K%
    LOOP UNTIL LEN(UnCompr$) = 0


END SUB 'Huffman

SUB PqDownHeap(K%)
' Build and maintain an indirect heap on the frequency values (P. 139)
'     reversing the inequalities since we want the smallest values first.

    SHARED N%,Heap%(),Count%()
    LOCAL J%,V%,Limit%
    V%=Heap%(K%) : Limit% = N%/2
    DO WHILE K% <= Limit%
       J%=K%+K%
       IF J%<N% THEN IF Count%(Heap%(J%)) > Count%(Heap%(J%+1)) THEN INCR J%
       IF Count%(V%)<=Count%(Heap%(J%)) THEN Heap%(K%)=V% : EXIT SUB
       Heap%(K%)=Heap%(J%) : Heap%(J%)=V% : K%=J%
    LOOP
END SUB 'PqDownHeap

'**********************************************************************
FUNCTION Bin2Int(X$)
X$=RTRIM$(X$) :X$=LTRIM$(X$) : Ll%=LEN(X$) : Ex%=0 : Tot%=0 : I%=Ll%
    DO WHILE I% > 0
        IF MID$(X$,I%,1)="1" THEN Tot&=Tot&+(2^Ex&)
        INCR Ex& : DECR I% : WEND
    Bin2Int=Tot&
END FUNCTION 'Bin2Int