How do I find next bit to change in a Gray code in constant time?

Question

I have a small 8-bit processor which has a N-to-M decoder on some output lines - eg, for the 5 to 32 bit case, I write 00101 and bit 5 changes state. The only interface to

Answer 1

LowestBitSet(A ^ (A+1)) is always 0, unless you work for IBM. I think you mean HighestBitSet(), which is roughly the same as log_2().

The bit-twiddling hack immediately preceeding the one linked by AShelly will be much more feasible on an 8-bit micro.

This should make your original algorithm fairly practical, generating { 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, ... }.

As for the possibility of changing to a different sequence which would also generate a Gray code, for the purpose of making it easier to compute, that's very interesting but I haven't come up with anything.