Method CountBits

avida-core/source/tools/cBitArray.cc:87–100

This technique counts the number of bits; it loops through once for each bit equal to 1. This is reasonably fast for sparse arrays.

// This technique counts the number of bits; it loops through once for each
// bit equal to 1.  This is reasonably fast for sparse arrays.
int cRawBitArray::CountBits(const int num_bits) const
{
  const int num_fields = GetNumFields(num_bits);
  int bit_count = 0;
  
  for (int i = 0; i < num_fields; i++) {
    int temp = bit_fields[i];
    while (temp != 0) {
      temp = temp & (temp - 1);
      bit_count++;
    }
  }
  return bit_count;
}

// This technique is another way of counting bits; It does a bunch of
// clever bit tricks to do it in parallel in each int.