In the code snippet at the bottom, there's this bit:

  for (i=2; i<fftFrameSize-2; i+=2) {
      for (bitm=2, j=0; bitm<fftFrameSize; bitm<<=1) {
          if (bitm & i) j++;
          j <<= 1;
      }
      if (i < j) { /* swap fftBuffer+i with fftBuffer+j */ }
  }

Near as I can tell, j is i reversed and left-padded with zeroes. What does the conditional translate to?