8a71ebf5bc
git-svn-id: https://svn.code.sf.net/p/kolmck/code@67 91bb2d04-0c0c-4d2d-88a5-bbb6f4c1fa07
101 lines
2.6 KiB
ObjectPascal
101 lines
2.6 KiB
ObjectPascal
unit URangeDecoder;
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{$IFDEF FPC}
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{$MODE Delphi}
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{$ENDIF}
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interface
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uses KOL,ULZMACommon;
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type PRangeDecoder = ^TRangeDecoder;
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TRangeDecoder=object(TObj)
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public
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Range,Code:integer;
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Stream:PStream;
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procedure SetStream(const AStream:PStream);
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procedure ReleaseStream;
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procedure _Init;
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function DecodeDirectBits(const AnumTotalBits:integer):integer;
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function DecodeBit(var Aprobs: array of smallint;const Aindex:integer):integer;
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end;
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procedure InitBitModels(var Aprobs: array of smallint);
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implementation
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const kTopMask = not ((1 shl 24) - 1);
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kNumBitModelTotalBits = 11;
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kBitModelTotal = (1 shl kNumBitModelTotalBits);
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kNumMoveBits = 5;
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procedure TRangeDecoder.SetStream(const AStream:PStream);
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begin
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self.Stream:=AStream;
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end;
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procedure TRangeDecoder.ReleaseStream;
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begin
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stream:=nil;
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end;
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procedure TRangeDecoder._Init;
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var i:integer;
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begin
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code:=0;
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Range:=-1;
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for i:=0 to 4 do begin
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code:=(code shl 8) or byte(ReadByte(stream));
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end;
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end;
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function TRangeDecoder.DecodeDirectBits(const AnumTotalBits:integer):integer;
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var i,t:integer;
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begin
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result:=0;
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for i := AnumTotalBits downto 1 do begin
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range:=range shr 1;
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t := ((Code - Range) shr 31);
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Code := Code - Range and (t - 1);
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result := (result shl 1) or (1 - t);
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if ((Range and kTopMask) = 0) then begin
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Code := (Code shl 8) or ReadByte(stream);
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Range := Range shl 8;
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end;
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end;
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end;
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function TRangeDecoder.DecodeBit(var Aprobs: array of smallint;const Aindex:integer):integer;
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var prob,newbound:integer;
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begin
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prob:=Aprobs[Aindex];
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newbound:=(Range shr kNumBitModelTotalBits) * prob;
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if (integer((integer(Code) xor integer($80000000))) < integer((integer(newBound) xor integer($80000000)))) then begin
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Range := newBound;
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Aprobs[Aindex] := (prob + ((kBitModelTotal - prob) shr kNumMoveBits));
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if ((Range and kTopMask) = 0) then begin
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Code := (Code shl 8) or ReadByte(stream);
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Range := Range shl 8;
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end;
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result:=0;
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end else begin
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Range := Range - newBound;
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Code := Code - newBound;
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Aprobs[Aindex] := (prob - ((prob) shr kNumMoveBits));
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if ((Range and kTopMask) = 0) then begin
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Code := (Code shl 8) or ReadByte(stream);
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Range := Range shl 8;
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end;
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result:=1;
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end;
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end;
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procedure InitBitModels(var Aprobs: array of smallint);
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var i:integer;
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begin
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for i:=0 to length(Aprobs)-1 do
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Aprobs[i] := kBitModelTotal shr 1;
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end;
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end.
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