[spc476]

And I find the bit manipulations easier to grok (then again, I know several different assembly languages and have been programming in C for years).

As for the bit ranges, it looks backwards to me, since bits are normally numbered high to low. I would find it easier to read if it read:

    self.0.set_range(3..0, stack_index);

I can "see" that much easier.

[tatterdemalion]

Well, Rust supports both bitwise manipulations and a range-based interface, so people from various backgrounds can use whichever they find more natural. :-)

[krupan]

Agreed, definitely should go high to low.