On Fri 13 Nov 2015 11:22, Zefram <zef...@fysh.org> writes: > With Guile 2.0.11: > > scheme@(guile-user)> (ash 123 (ash -1 63)) > $1 = 123 > > Correct result would of course be zero. Problem only occurs for > exactly this shift distance: one bit less produces the right answer. > Problem also occurs on Guile 1.8.8. Looking at the implementation, > the problem is attributable to the negation of the shift distance, > which in twos-complement fails to produce the expected positive result. > > Note the resemblance to bug #14864, fixed in 2.0.10. This bug is of > very similar form, but is distinct. The test cases of #14864 pass for > me on the 2.0.11 that shows the problem with a 2^63 bit shift. My bug > does occur with the rnrs bitwise-arithmetic-shift-right, which was used > in #14864, as well as with ash.
Fascinating, thank you! Also occurs on 2.1.3. Andy
