How to fix this non-recursive odd-even-merge sort algorithm?

Question

I was searching for non-recursive odd-even-merge sort algorithm and found 2 sources:

• a book from Sedgewick R.
• this SO question

Both alg

Answer 1

I think I found a solution. I checked it for length = 2, 4, 8, 16.

Here is my code:

void sort(int length)
{ int G = log2ceil(length);                      // number of groups
  for (int g = 0; g < G; g++)                    // iterate groups
  { int B = 1 << (G - g - 1);                    // number of blocks
    for (int b = 0; b < B; b++)                  // iterate blocks in a group
    { for (int s = 0; s <= g; s++)               // iterate stages in a block
      { int d = 1 << (g - s);                    // compare distance
        int J = (s == 0) ? 0 : d;                // starting point
        for (int j = J; j+d < (2<

This solution introduces a fifth for-loop to handle subblocks in a group. The j loop has a changed start and abort value to handle odd counts of post merge steps without generating doubled compare steps.