This will create easily solved breakage on updates but
I figure it's best to pull the band aid off as early as possible

Standard library does this too. Unfortunate wish they just exposed it in the
standard library. Perhaps we can isolate the specific code we need later.

I'm just not good enough at assembly. I added tests to confirm that @wdvxdr's
implementation works correctly and matches the output of the basic masking loop.

Closes #64