Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!iuvax!uceng!ranga
From: ranga@uceng.UC.EDU (Dr. Ranga R. Vemuri)
Newsgroups: comp.lang.prolog
Subject: Sicstus Prolog Questions
Keywords: Sicstus0.6 Prolog, Floating Point Arithmetic, Foreign Fns.
Message-ID: <5574@uceng.UC.EDU>
Date: 22 Jul 90 11:09:12 GMT
Organization: College of Engg., Univ. of Cincinnati
Lines: 61

(1)
I am using Sicstus0.6 prolog to write a program with a LOT of
floating-point operations.  I am having problems in getting
the program perform these floating point operations correctly.
It seems that, after performing a few thousand operations,
the floating point results start overflowing or underflowing.

For example,  here is a simple psuedo random number generator.
IX is the seed.  This produced about 700 to 800 random numbers correctly 
(I checked them through other means) and then started giving out 0's;
The reason, I found through tracing, invariably was an underflow/overlow.
At that point, the prolog system wouldn't do even simple arithmetic 
properly: for eg, `A is 1/6' produces `A = 4.32583271660369e-308' !!!


random(IX, NewIX, Rand):-
        A     is   16807,
        B15   is   32768,
        B16   is   65536,
        P     is   2147483647,
        XHI is IX//B16,
        XALO is (IX-(XHI*B16))*A,
        LEFTLO is XALO//B16,
        FHI is (XHI*A) + LEFTLO,
        K is FHI//B15,
        ModifiedIX is ( ((XALO-(LEFTLO*B16))-P) + (FHI-(K*B15))*B16) + K,
        ((ModifiedIX < 0, NewIX is ModifiedIX + P); NewIX is ModifiedIX),
        Rand is NewIX*4.656612875e-10.


Any suggestions on how I can try and get of out this problem will be
greatly appreciated.

(2)
As one way of avoiding the above problem, I have tried to implementing
my floating point routines in C and tried to interface them using
the foreign language interface feature of Sisctus.  I couldn't get
that working either.  'load_foreign_files' gives me either
an 'illegal usage' message or says 'myCfile.o undefined'.
'foreign' and 'foreign_file' also give 'illegal usage' messages.
The Sictus0.6 documet I have seems to imply, however, that this feature is
fully implemented....

Any help here is appreciated too......

(3)
Is there a free-of-charge (ftp'able ??) or commercial prolog
which is known to be good in handling both floating point arithmetic 
and foreign function interface ??


Thanks.

- Ranga
  ranga@uceng.uc.edu
_________
Ranga Vemuri                                     ranga@uceng.uc.edu
Laboratory for Digital Design Environments           (513)-556-4784
M.L. 30, Dept. Electrical & Computer Engineering     (513)-556-4769  
University of Cincinnati, Cincinnati, OH 45221, USA