Method writeCorrector

LASzip/src/integercompressor.cpp:364–465

*/

void IntegerCompressor::writeCorrector(I32 c, ArithmeticModel* mBits)
{
  U32 c1;

  // find the tighest interval [ - (2^k - 1)  ...  + (2^k) ] that contains c

  k = 0;

  // do this by checking the absolute value of c (adjusted for the case that c is 2^k)

  c1 = (c <= 0 ? -c : c-1);

  // this loop could be replaced with more efficient code

  while (c1)
  {
    c1 = c1 >> 1;
    k = k + 1;
  }

  // the number k is between 0 and corr_bits and describes the interval the corrector falls into
  // we can compress the exact location of c within this interval using k bits

  enc->encodeSymbol(mBits, k);

#ifdef COMPRESS_ONLY_K
  if (k) // then c is either smaller than 0 or bigger than 1
  {
    assert((c != 0) && (c != 1));
    if (k < 32)
    {
      // translate the corrector c into the k-bit interval [ 0 ... 2^k - 1 ]
      if (c < 0) // then c is in the interval [ - (2^k - 1)  ...  - (2^(k-1)) ]
      {
        // so we translate c into the interval [ 0 ...  + 2^(k-1) - 1 ] by adding (2^k - 1)
        enc->writeBits(k, c + ((1<<k) - 1));
#ifdef CREATE_HISTOGRAMS
        corr_histogram[k][c + ((1<<k) - 1)]++;
#endif
      }
      else // then c is in the interval [ 2^(k-1) + 1  ...  2^k ]
      {
        // so we translate c into the interval [ 2^(k-1) ...  + 2^k - 1 ] by subtracting 1
        enc->writeBits(k, c - 1);
#ifdef CREATE_HISTOGRAMS
        corr_histogram[k][c - 1]++;
#endif
      }
    }
  }
  else // then c is 0 or 1
  {
    assert((c == 0) || (c == 1));
    enc->writeBit(c);
#ifdef CREATE_HISTOGRAMS
    corr_histogram[0][c]++;
#endif
  }