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Ekey, posted Mon Nov 02, 2015 12:12 pm (9212)

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There is a realization of LZW algorithm is similar to the code below?

Code:

int LZWEncode(unsigned char* pScrBuffer, unsigned char* pDstBuffer) - It should return the compressed size
int LZWDecode(unsigned char* pScrBuffer, unsigned char* pDstBuffer) - It should return the decompressed size

I see only by file stream realizations. Like

Code:

void LZWEncode(FILE *fin, FILE *fout)
void LZWDecode(FILE *fin, FILE *fout)

aluigi, posted Mon Nov 02, 2015 1:15 pm (9215)

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Have you already checked quickbms?
I have seen many LZW* in various games and implemented lot of them so it's highly possible that it's already there.
And if it's there, there is also the source code for performing the memory->memory decompression.

Ekey, posted Mon Nov 02, 2015 2:36 pm (9219)

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Yeah, I already checked QuickBMS source's. Correct algorithm is clzw for The Binding of Isaac compressed data, but it also works like FileIn, FileOut

Code:

   lzw_dec_init(ctx, fout);
   while (len = lzw_readbuf(fin, buf, sizeof(buf)))
   {
      int ret = lzw_decode(ctx, buf, len);
      if (ret != len)
      {
         fprintf(stderr, "Error %d\n", ctx);
         break;
      }
   }

aluigi, posted Mon Nov 02, 2015 4:59 pm (9222)

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100% memory2memory or quickbms doesn't use it
From src/perform.c:

Code:

            lzw_dec_t  *clzw_ctx;
            clzw_ctx = calloc(1, sizeof(lzw_dec_t));
            if(!clzw_ctx) STD_ERR(QUICKBMS_ERROR_MEMORY);
            clzw_outsz = 0;
            lzw_dec_init(clzw_ctx, out);
            lzw_decode(clzw_ctx, in, zsize);
            size = clzw_outsz;
            FREE(clzw_ctx);

Ekey, posted Mon Nov 02, 2015 5:33 pm (9230)

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Here is my attempt to do something like this

Code:

int LZWDecode(unsigned char* pScrBuffer, unsigned char* pDstBuffer)

But in the output buffer I see incorrect data.

QuickBMS result with 1024 bytes is:

Code:

   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   Code:

   

aluigi, posted Mon Nov 02, 2015 5:47 pm (9232)

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Why don't have you used lzw-dec.c in your code?
Your implementation of clzw is a bit different than the library.

Ekey, posted Mon Nov 02, 2015 6:05 pm (9236)

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I do not see the difference, because give identical good results in 1024 bytes: QuickBMS library (lzw-dec.c) and (Google Code lzw.c)

Ekey, posted Mon Nov 02, 2015 6:32 pm (9238)

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Ok seems found problem

After part

Code:

        strlen = lzw_get_str(ctx, nc, buff, sizeof(buff));
        c = buff[sizeof(buff) - strlen];
        memcpy(pDstBuffer, buff (sizeof(buff) - strlen), strlen);

Add

Code:

       for(int i = 0; i < strlen; i  )
           pDstBuffer  ;

Decompressed size:

Code:

return isize * 2   1; //  1 mean first byte which is copied

Ekey, posted Mon Nov 02, 2015 8:47 pm (9242)

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Well, the problem is still there, not all blocks can be decompressed, god damn! QuickBMS also give invalid dump

Chunk 1: Offset at 0xE > ZSize is 602 - Valid dump
Chunk 2: Offset at 0x26C > ZSize is 436 - Invalid dump

aluigi, posted Mon Nov 02, 2015 10:06 pm (9245)

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I tried also to concatenate chunk1 and chunk2 but it fails too.