Date: Sat, 12 Nov 1994 23:07:53 -0500 (CDT)
From: Aaron Ucko <UCKO AT VAX1 DOT ROCKHURST DOT EDU>
Subject: Re: DJGPP & MATH
To: BILLM AT vaxc DOT cc DOT monash DOT edu DOT au
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu
Organization: Rockhurst College; Kansas City, MO

>Andras Solyom ("solyom AT bmeik DOT eik DOT bme DOT hu") wrote:
>
>>As I read much about floating point errors in GCC 1.12 or 1.11 nowdays,
>>maybe it is worthwile to report about my experinences.
>>I was given a C program written by Steven Pemberton (steven.cwi.nl)
>>which tests the capabilities of a C compiler. The copy I have is of Ver. 4.2.
>>I compiled and run it succesfully with TURBO C and C++ (Version 1.0 -2.0),
>>BORLAND C++ (Version 3.0, 3.1 and 4.0) compilers AND with DJGPP 1.09.
>>I switched on DJGPP 1.11 maint 5 a while ago and now it occured to me that
>>I gave the new compiler a test, and found out that it just crashes as you see:
>>
>
>then Aaron Ucko ("UCKO AT VAX1 DOT ROCKHURST DOT EDU") followed with:
>
>>Never mind; I ran across the latest version (5.0) and decided to try it 
>>myself.  It also crashes under DJGPP, but at a _much_ more sensible place:
>>when trying to divide by 0 (although it should have triggered a trap rather
>>than a floating point exception...)   What's _really_ interesting is that
>>
>
>Every now and then someone gets one of these test programs, runs it,
>and then proclaims that they have discovered a bug in the floating
>point code of gcc.  Usually (if not always?), the fault is found to
>lie in the test program.  The code produced by gcc is not perfect but,
>as far as I know, it doesn't have any of the obvious bugs which these
>programs purport to test for.

I'd be about the last person to criticize GCC.  What I am criticizing is
DJGPP's (mis-)initialization of the FPU (which was mentioned in different
guise a little while ago)
>
>It is quite difficult to make a good floating point test program.  The
>problem is that there are a lots of possible gotchas allowable in 'C'
>when you try to test the margins.  Probably the best program which I
>have seen is `paranoia' (available on netlib).  It doesn't crash, but
um...where's netlib?
>will report that the floating point has one(*) flaw (paranoia is
>wrong).  This venerated program is very good but not perfect.
>
>(*) You may find that it reports more flaws or errors if you use a
>floating point emulator other than wmemu1xx.

We aren't talking about _emulators_ here (although if they're truly good
they'll have the same problem :-) ), but about actual FPUs and DJGPP's
misconfiguration thereof.

--- Aaron Ucko (ucko AT vax1 DOT rockhurst DOT edu; finger for PGP public key) -=- httyp!
-=*=-Just because you're paranoid doesn't mean they aren't out to get you.-=*=-
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