[emn13]

fastest would likely be to wrap at the greatest multiple of N that fits in your integer representation, since that (probably dramatically) reduces branch mispredicts.

However, you're still doing lots of modulos to then find the "real" array index from the "virtual" one, so this is still likely not a great option compared to the power-of-two buffers.

It might actually be faster (at least for mildly large buffers) to use 2 ifs and a range that's twice the capacity. One ifs checks whether your virtual index needs to subtract the capacity to become real, and another checks whether it's time to substract 2 times the capacity.

[dllthomas]

With the conditional subtraction recommended elsewhere, you can do 2*N with no branch mispredictions and no modulo. Whether that's actually faster should be tested, if you're in an environment where you care about such things.