Whoops! You're right, of course. Sorry for the confusion. (I'd never read the errata - lots of neat stuff in there.)
On Sep 18, 2017 2:30 AM, "Mark H Weaver" <m...@netris.org> wrote: > Mark H Weaver <m...@netris.org> writes: > > > Julian Graham <jool...@gmail.com> writes: > > > >> It looks like there was a subtle but significant regression introduced > >> to the behavior of `bitwise-copy-bit' in `(rnrs arithmetic bitwise)' > >> back in 93da406f33. > >> > >> R6RS says [0] that function (with arguments EI1, EI2, EI3) should > >> transfer the EI2th bit from EI3 to EI1, but Guile's implementation was > >> always reading the 0th bit from EI3. > > > > I was puzzled by this, because the same specification also states that > > "ei3 must be either 0 or 1", > > Also note that the same specification also states that the result of > (bitwise-copy-bit ei1 ei2 ei3) is the same as the result of: > > (let* ((mask (bitwise-arithmetic-shift-left 1 ei2))) > (bitwise-if mask > (bitwise-arithmetic-shift-left ei3 ei2) > ei1)) > > and this unambiguously required that the 0th bit of 'ei3' is the bit > that is copied. > > Mark >
