After exchanging a few private emails with Mr. Carter it becomes clear that the real problem is that he tries to give a floating point number to ~r, while at least the current SBCL insists that he should use an INTEGER.  Size of the number is irrelevant.

As this is just SBCL enforcing what the standard says it is not a bug.  While I have no old versions available, I suspect SBCL used to be sloppier about this earlier so that his code suddenly stop working now that this is actually enforced.

Stig Hemmer