Duplicated code in DecompressZip and DecompressRLE

[jeffatrad]

There is a chunk of code at the end of both decompresszip and decompressrle that is just cut and pasted.

If you split this out into and undo_predictor and undo_reorder and then just call them, and then do a little IPC unrolling, this will simplify the code and run about 10% faster for 4K RLE loads:

static void undo_predictor( unsigned char * t, unsigned long uncompressed_size )
{
    unsigned char *stop = t + uncompressed_size;
    int tm1 = 128;

    if ( uncompressed_size >= 16 ) // for some minimum size
    {
      unsigned char *stop4 = t + (uncompressed_size&~3);
      while (t < stop4) {
        int t0 = t[0];
        int t1 = t[1];
        int t2 = t[2];
        int t3 = t[3];

        t[0] = static_cast<unsigned char>(tm1+t0-128);
        t[1] = static_cast<unsigned char>(tm1+t0-128+t1-128);
        t[2] = static_cast<unsigned char>(tm1+t0-128+t1-128+t2-128);
        t[3] = tm1 = static_cast<unsigned char>(tm1+t0-128+t1-128+t2-128+t3-128);

        t += 4;
      }
    }

    while (t < stop) {
      int d = tm1 + int(t[0]) - 128;
      t[0] = tm1 = static_cast<unsigned char>(d);
      ++t;
    }
}

static void undo_reorder( unsigned char *dst, unsigned char *t, unsigned long uncompressed_size )
{
  const char *t1 = reinterpret_cast<const char *>(t);
  const char *t2 = reinterpret_cast<const char *>(t) +
                   (uncompressed_size + 1) / 2;
  char *s = reinterpret_cast<char *>(dst);
  char *stop = s + (uncompressed_size);
  char *stop8 = s + (uncompressed_size&~7);

  while( s < stop8 )
  {
    s[0]=t1[0];
    s[1]=t2[0];
    s[2]=t1[1];
    s[3]=t2[1];
    s[4]=t1[2];
    s[5]=t2[2];
    s[6]=t1[3];
    s[7]=t2[3];
    t1 += 4;
    t2 += 4;
    s += 8;
  }

  for (;;) {
    if (s < stop)
      *(s++) = *(t1++);
    else
      break;
    if (s < stop)
      *(s++) = *(t2++);
    else
      break;
  }
}

Even if you don't do initial unrolled loop, it would be good to deduplicate this code.

Thanks!

[syoyo]

Please send PR of this change.

[syoyo]

Close the issue since there is no PR has been submitted