Currently there's no direct way to restrict what goes into the random
tester, so it will stimulate all those other bugs as well.
I should probably rewrite the thing and move it into the SBCL
repository. If this happens I'll keep your requirement (to be able
to restrict the set of productions) in mind.
On Fri, Mar 30, 2012 at 11:39 AM, Christophe Rhodes <csr21@...> wrote:
> Christophe Rhodes <csr21@...> writes:
>> This one, I think, is my fault; I haven't bisected, but I think I
>> probably introduced a bug over four years ago in modular arithmetic,
>> thinking that one can use a signed modular arithmetic implementation of
>> an unsigned computation, if the width is smaller. Unfortunately, that's
>> not quite true; here, SBCL successfully derives that the result of F1
>> will be a positive fixnum, but it then computes the addition using
>> signed modular arithmetic, which has rather more 1 bits than either the
>> true or the unsigned modular arithmetic version. I think this would be
>> correct if the constant here were cut to the correct (unsigned) width,
>> or more generally if the LOGAND optimizer were to wrap itself in
>> another, simply masking, LOGAND.
> I have a fix for this, I think. I'd quite like to run the random tester
> myself on a fixed tree; "I have merely proved it correct, not tried
> it". How are you running it? Is there a way of running it restricting
> its scope to relatively simple forms like the above, to avoid running
> into the other problems you've found?
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