Still doesn't work going end to start. src starts at 50, ends at 100 dst starts at 25, ends at 75. First we copy 100 to 75, then 99 to 74, etc ... now

Still doesn't work going end to start. src starts at 50, ends at 100 dst starts at 25, ends at 75. First we copy 100 to 75, then 99 to 74, etc ... now we get to copy from 75 to 50, but we've overwritten it already!