Most architectures seem to have an instruction for finding the leftmost set bit in a word [1] and most major C/C++ compilers/libraries have a function for it [2].

I wonder how using that would compare?

You'd find the leftmost bit, invoke the func_true for that, and clear the leftmost bit.

Then loop finding the leftmost bit, invoking the func_false for the bits between the current leftmost bit and the previous leftmost bit, func_true for the leftmost bit, and then clear that bit.

I wouldn't expect it to be dramatically different, but it is trading test and clear on the off bits and a conditional branch off of the result for a loop calling func_false a predetermined number of times. One of those options might be a little faster than the other.

[1] https://en.wikipedia.org/wiki/Find_first_set#Hardware_suppor...

[2] https://en.wikipedia.org/wiki/Find_first_set#Tool_and_librar...