Date: Mon, 9 Jun 1997 17:43:42 -0700 (PDT)
Message-Id: <199706100043.RAA07809@adit.ap.net>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
To: tudor AT cam DOT org
From: Nate Eldredge <eldredge AT ap DOT net>
Subject: Re: Possible bug?
Cc: djgpp AT delorie DOT com
Precedence: bulk

Vic wrote:
>Philip Ibis wrote:
>> It might be due to the fact that I'm using v2.00, if so, then, oops.
>I'm using 2.01 . 
>> Anyways... The following program gives my system a wedgie.
>On mine it crashes. Tracebacks attached to the mail. 
>> ---- snip snip ---
>> #include <stdio.h>
>> #include <string.h>
>> int main(void)
>> {
>>   double n;
>>   memset(&n,0xFF,sizeof(double));  /* contrived, sure */
>>   printf("%f\n",n);
>> }
>

I'd say it's a good guess that a double made of 0xFF's is not a valid
floating point number. I don't claim to be an 80x87 guru but I know you
can't just load any old garbage into a FPU register and expect it to work.
The reason it crases inside printf is that printf was the unlucky one who
had to do floating point stuff to it :) (Before it just hung around on the
stack.)

I can't see any reason why you'd want to have a double of 0xFF's. This is
why you convert to doubles with = and not memset(). Floating point numbers
are formatted all funny, with mantissas, exponents, and all that good stuff.
:) If you want the largest allowable double, you have MAXDOUBLE from
<values.h>. If you're *really* interested, you could read some IEEE
standards. (yeah, right.)

So, in answer to the problem, "don't do that, then." ;-)
--------------------
Nate Eldredge
eldredge AT ap DOT net