From: Endlisnis <s257m AT unb DOT ca>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Am I retarded -or- Why is my exe size so big?!?
Date: Sun, 30 Aug 1998 12:21:05 -0300
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Eli Zaretskii wrote:
> > > Actually it states that -O2 is the best optimizations switch without a
> > > speed/size tradeoff.
> >       But, -O1,2 or 3 sometimes make programs that don't do what you might
> > expect/desire.  I have a few VERY LONG programs that do not do the same stuff
> > when compiled with any optimizations on.  They are fully ANSI compilent
> > programs not trying to do anything tricky.
> 
> It is a bug when a program behaves differently under different
> optimization switches.  Usually, the bug is in the application code,
> not in the compiler.  Unless these programs explore the fine details
> of machine arithmetics, which AFAIK is the only case when
> optimizations should NOT be used, you need to debug those programs,
> I'd say.
	Well, I run everything through RHIDEv1.4, and for some reason, the debugger
won't touch my code.  It just skips right to the end.  And even if I convince
it to walk through parts of my code, I can't watch half the variables.  When
I'm in the correct context for that variable, it still says "Not Avaiable".

	On a slightly different subject, here's a line of code which doesn't do what
I expect (under any optimization level including none):

#include <iostream.h>

typedef unsigned int lword;

int main()
{
 short* DOS = 0xC0001234;  //C000:1234 = 000C1234 linear address
 DOS = (short*)(((lword)DOS>>12)&0xFFFF0)+((lword)DOS&0xFFFF);
 cout << DOS << " should be 0xC1234\n";
 return 0;
 }

Output:
0xc2468 should be 0xC1234

	This is a shortend version of code that needs to get data from an SVGA
function that returns SEG:OFFSET info and I need to convert it to a linear
address.  If I use a temporary variable of type 'lword', and do the exact same
line of code (without the casting) it works perfectly.

-- 
     (\/) Endlisnis (\/)
          s257m AT unb DOT ca
          Endlisnis AT GeoCities DOT com
          Endlis AT nbnet DOT nb DOT ca