How good your knowledge of bitwise tricks? Exercise.

I searched for rotate left/right function in pure C and found this:

uint32_t rotl32 (uint32_t x, uint32_t n)
        assert (n<32);
        return (x<<n) | (x>>(-n&31));

Ouch! John Regehr provided only rotate left function without corresponding right one. But I can manage this! I can reimplement rotr() using rotl(). My function is:

uint32_t rotr32_my(uint32_t x, uint32_t n)
        return ??? rotl32(?, ?) ???;

In my case, the length of "return ??? rotl32(?, ?) ???;" is 23 characters. If you can reimplement rotate right using only rotate left, your solution shouldn't be any longer.

In the same way, ROR x86 assembly instruction can be implemented using ROL. How?

UPD: the answer.

(the post first published at 20220914.)

List of my other blog posts.

Subscribe to my news feed

Yes, I know about these lousy Disqus ads. Please use adblocker. I would consider to subscribe to 'pro' version of Disqus if the signal/noise ratio in comments would be good enough.