[lkml]   [2001]   [Aug]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    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 <> 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
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2005-03-22 13:01    [W:0.032 / U:12.416 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site