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. -zefram
