Re: Subtraction + comparison in one asm instruction?

Gabriel Dos Reis <gdr@integrable-solutions.net> wrote:
> "VBDis" <vbdis@aol.com> writes:
>
>> The conversion of formulas,
>> according to algebraic rules, IMO is independent from the ranges of
>> the data types which are used in actual source code.
>
> No, that is not true in C, nor in C++ for example.
>
> On a machine set up to trap when an overflow occurs, the behaviour for
> the strict semantics of "(x + 1) - 1" is to trap when
> x == INT_MAX for example, while the transformed version will not trap:
> The net result is that the semantics of the transformed expression no
> longr match that of the untouched one.


It would be far easier to do such an optimisation only on machines
without over/underflow traps. Seeing their machine being the slowest
around would then teach the machine manufacturers to not make such in
the future...
--
Sander

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