How to rewrite array from row-order to column-order?

Question

I have this double for-loop, where I have both row-order and column-order array indexing, which should be bad for performance.

  for (int row = 0; row < h         


        

Answer 1

So you want to switch from something like:

0  1  2  3
4  5  6  7
8  9  10 11

to

0  3  6  9
1  4  7  10
2  5  8  11

?

Try

for (int i = 0; i < width; ++i)
  for (int j = 0; j < height; ++j)
    array_b[ i * height + j ] = array_a[ j * width + i ];