Package RCL and Inf

Question

Hi, this will be a difficult question to answer, I contacted the author but still no replies I'll give it a shot here: In the package RCL (http://common-lisp.net/project/rcl/) examples:

(in-package :rcl) (r-init)

(r "/" 1 5) RCL> 0.2d0

(r "print" (r% "/" 1 5)) RCL> ;R# 1 0.2 0.2d0

The above is ok, but (r "/" 1 0) RCL>> # broken

(r "print" (r% "/" 1 0)) RCL>> ;R# 1 Inf

broken

or (r "log" 0)

How to get around this so that when R gets to an inf value my lisp doesn't break but just gives a message that an inf value is computed; The above is a simple example but there are times when we have during a statistical procedure divisions by zero that nevertheless do not invalidate the results and R returns a final value (like during optimization), but this unfortunately crashes while using RCL.

Answer 1

Ok I got the answer from the author I post here: support for IEEE floating-point infinities is platform-dependent. The following lisps work, at least on this system (MacOSX):

SBCL R> (r "/" 1 0) .SB-EXT:DOUBLE-FLOAT-POSITIVE-INFINITY R> (r "log" 0) .SB-EXT:DOUBLE-FLOAT-NEGATIVE-INFINITY

Allegro CL R> (r "/" 1 0) .EXCL:INFINITY-DOUBLE R> (r "log" 0) .EXCL:NEGATIVE-INFINITY-DOUBLE

LispWorks R> (r "/" 1 0) +1D++0 #| +1D++0 is double-float plus-infinity R> (r "log" 0) -1D++0 #| -1D++0 is double-float minus-infinity

CMUCL doesn't (X86:SIGFPE-HANDLER, no exceptions enabled), but I think this can be fixed (http://common-lisp.net/project/cmucl/doc/cmu-user/extensions.html#float-traps).

ECL is the last one that I tried, and it's apparently the one you use (I got the same FLOATING-POINT-OVERFLOW exception). It seems that it also allows to disable overflow checks using SI:TRAP-FPE, this might be what you need (the following example is taken from http://www.lispforum.com/viewtopic.php?f=2&t=386):

(let* ((bits (si::trap-fpe 'last nil))) (prog1 (/ 1.0 0.0) (si::trap-fpe bits t))) .SI:SINGLE-FLOAT-POSITIVE-INFINITY