[stonegray]

If you're gonna test the i--, shouldn't it fall through on zero anyway?

    for (unsigned int i = N; i--;){}

    unsigned int i = N;
    while(i--){ ... }

Also I think I'm missing the tricky part. Couldn't this be a bog-standard for loop?

   for (unsigned int i = N - 1; i > 0; i--){ ... }

The "downto" pseudooperator definitely scores some points for coolness and aesthetics, but there's no immediately obvious use case for me.

[Jorengarenar]

The former executes loop when `i` is 0.

And we cannot change the comparison to `>=` in the later, because unsigned is always bigger or equal 0, thus we would get infinite loop.