multiplies by powers of two

[Matthew Fluet]

> With regards to the 2 shifts, couldn't you save the flags register in some
> other register and then or it back with the flags and look if either set the
> overflow?  Maybe that requires pushing it on the stack?

Looks like you would need to add, LAHF (load EFLAGS into AH), copy it to
another 16 bit regiter, do the second add, LAHF again, or, then SAHF (set
EFLAGS from AH).  Sounds like too many instructions.

BTW, I converted 2829 cmp's with 0 to tst's in a self compile.