decompress/source/lzss.c

#include <string.h>
#include "decompress.h"

void lzssDecompress(const u8 *src, u8 *dst, int size) {
  unsigned char flags = 0;
  unsigned char mask  = 0;
  unsigned int  len;
  unsigned int  disp;

  while(size > 0) {
    if(mask == 0) {
      // read in the flags data
      // from bit 7 to bit 0:
      //     0: raw byte
      //     1: compressed block
      flags = *src++;
      mask  = 0x80;
    }

    if(flags & mask) { // compressed block
      // disp: displacement
      // len:  length
      len  = (((*src)&0xF0)>>4)+3;
      disp = ((*src++)&0x0F);
      disp = disp<<8 | (*src++);

      size -= len;

      // for len, copy data from the displacement
      // to the current buffer position
      memcpy(dst, dst-disp-1, len);
      dst += len;
    }
    else { // uncompressed block
      // copy a raw byte from the input to the output
      *dst++ = *src++;
      size--;
    }

    mask >>= 1;
  }
}