[fpc-pascal] LZMA Algorithm fails on 64bit
joshyfun at gmail.com
Tue Jan 26 00:09:18 CET 2010
Monday, January 25, 2010, 7:14:05 PM, you wrote:
>> I hope to have some spare time this afternoon to test it, as I also
>> need LZMA decompress in 64 bit.
MK> I checked it: Decompressing files on 64bit-machines which were compressed
MK> on 32bit-linux does not work. Which means:
MK> 32bit-compressed -> 32bit-decompression ==> Works!
MK> 64bit-compressed -> 64bit-decompression ==> Does not work
MK> 64bit-compressed -> 32bit-decompression ==> Works!
MK> 32bit-compressed -> 64bit-decompression ==> Does not work.
Found the bug in URangeDecoder.pas
function TRangeDecoder.DecodeDirectBits(const numTotalBits:integer):integer;
for i := numTotalBits downto 1 do begin
range:=range shr 1;
//t := ((Code - Range) shr 31);
t := (DWORD(Code - Range) shr 31);
Code := Code - Range and (t - 1);
result := (result shl 1) or (1 - t);
if ((Range and kTopMask) = 0) then begin
Code := (Code shl 8) or ReadByte(stream);
Range := Range shl 8;
DWORD fixes the problem, as:
32 bits: ($80000001 - 1) shr 31 = 1
64 bits: ($80000001 - 1) shr 31 = -1
64 bits: DWORD($80000001 - 1) shr 31 = -1
It looks like a problem in 64 bit versions :-? I think this topic
appears in the past about 32<->64 bits shift operations over signed
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