Finding the next in round-robin scheduling by bit twiddling

Question

Consider the following problem. You have a bit-string that represents the current scheduled slave in one-hot encoding. For example, \"00000100\" (with the leftmost bit being #7

Answer 1

This should do what you want:

number_of_tasks= 
next_mask= current | (current - 1);
next_barrel= next | (next << number_of_tasks);
next_barrel&= ~number_of_tasks;
next_barrel&= -next_barrel;
next_barrel|= next_barrel >> number_of_tasks;
next_task_mask= next_barrel & -next_barrel;

Basically, duplicate the bits of the next task mask, mask off the bits we don't want to consider, find the lowest set bit, fold the high bits back in, then take the lowest bit set. This runs in constant time.

Edit: Updating to take into account current == 00010000 and next_mask == 00111000