问题
Iterating forward through a circular buffer without using a conditional is easy with the remainder operator...
iterator = (iterator + 1) % buffer_size;
I can't for the life of me figure out the reverse operation, iterating backward.
回答1:
Does iterator = (iterator + buffer_size - 1) % buffer_size work for you? Go one less than all the way around.
回答2:
Borealid's answer works. (note: iterator is set to 0 initially).
Another solution is
iterator = buffer_size - 1 - (buffer_size - iterator) % buffer_size
with iterator set to buffer_size initially.
来源：https://stackoverflow.com/questions/3437477/how-do-you-iterate-backward-over-circular-buffer-without-a-conditional