using !

[Dave Gillett]

In <544 at taumet.com> steve at taumet.com (Stephen Clamage) writes:

>heroux at cemmva.cem.msu.edu (Brett Heroux) writes:
>>Is !(a > b) portable?
>>slower or faster than  a <= b?

>Depends on the compiler and machine.  Many compilers will generate
>identical code for both constructs.  You can look at the code your
>compiler generates for each construct, and if they are different,
>measure the time taken by each version.  If you choose one construct
>on this basis, you must realize that the next compiler or machine you
>use may not produce the same result.


     If you find a compiler that generates different code for the two cases,
it is most likely to have crudely generated code for the !(a > b) case, where
two different operators appear, rather than for the single operator in the
a <= b case.  So while a good compiler will generate the same code for both
cases, a bad compiler is likely to generate better code for the a <= b case.

                                                   Dave