lzw.c

   1 #include <string.h>
   2
   3 #define N 4096
   4
   5 #define OUT(X) if(out < outend) *(out++) = X; else return 0;
   6
   7 int lzwdecomp(unsigned char* in, unsigned long insz,
   8               unsigned char* out, unsigned long outsz)
   9 {
  10         unsigned char buf[N];
  11         unsigned char *inend = in+insz, *outend = out+outsz;
  12         int bits, len, mask, i = N - 16;
  13         while (1) {
  14                 if(in >= inend) return 0;
  15                 bits = *(in++);
  16                 for (mask = 1; mask & 0xFF; mask <<= 1) {
  17                         if (bits & mask) {
  18                                 if(in+2>inend) return 0;
  19                                 short tmp;
  20                                 memcpy(&tmp, in, 2);
  21                                 in += 2;
  22                                 int j = tmp;
  23
  24                                 len = ((j >> 12) & 15) + 3;
  25                                 j = (i - j - 1) & (N - 1);
  26
  27                                 while (len--) {
  28                                         buf[i] = buf[j];
  29                                         OUT(buf[i]);
  30                                         j = (j + 1) & (N - 1);
  31                                         i = (i + 1) & (N - 1);
  32                                 }
  33                         } else {
  34                                 if(in >= inend) return 0;
  35                                 buf[i] = *(in++);
  36                                 OUT(buf[i]);
  37                                 i = (i + 1) & (N - 1);
  38                         }
  39                         if(out == outend) break;
  40                 }
  41                 if(out == outend) break;
  42         }
  43         return 1;
  44 }