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SubjectRe: [IDEA+RFC] Possible solution for min()/max() war
David Weinehall wrote:
>
> On Thu, Aug 30, 2001 at 09:16:47PM +0000, Graham Murray wrote:
> > Daniel Phillips <phillips@bonn-fries.net> writes:
> >
> > > More than anything, it shows that education is needed, not macro patch-ups.
> > > We have exactly the same issues with < and >, should we introduce
> > > three-argument macros to replace them?
> >
> > Would it not have been much more "obvious" if the rules for
> > unsigned/signed integer comparisons (irrespective of the widths
> > involved) were
> >
> > 1) If the signed element is negative then it is always less than the
> > unsigned element.
> >
> > 2) If the unsigned element is greater than then maximum positive value
> > expressible by the signed one then it is always greater.
> >
> > 3) Only if both values are positive and within the range of the
> > smaller element are the actual values compared.
>
> Possibly, but changing the C specification is not really an option here...

Even worse: most microprosessors don't do comparisons that way.
They compare either two signed or two unsigned
items and do that reasonably fast. This is why C also works this way.

A compiler can be made to use the above standard, but it would generate
slow code for all signed/unsigned compares because now there is
3 tests instead of one. This is why language designers don't do that.

You can of course do this explicitly in code if you need that
sort of comparison, e.g.

signed a;
unsigned b;
if (a<0) case1()
else if (b>MAX_SIGNED) case2()
else if (a<b) case1() else case2();

A nice feature of C is that ugly time-consuming stuff tends to
look ugly and time-consuming in code too. So it is easier
to avoid. :-)

Helge Hafting
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