Steven Schveighoffer wrote:
> J�r�me M. Berger Wrote:
>
>> J�r�me M. Berger wrote:
>>> OK, I found a solution that is optimal in over 99% of the cases
>>> (99.195% to be precise), while still being fast (because it avoids
>>> looping over the bits):
>>>
>> I've run my function and Andrei's on all possible min, max pairs in
>> 0..299 without checking, just for the timing. On my computer (Athlon
>> X2 64 @2GHz), my function took 50s and Andrei's took 266s. The
>> difference should be even bigger for larger numbers.
>
> Can I ask, what is the point of having a non-exact solution (unless you are
> just doing this for fun)?
>
> We are talking about range propagation, a function of the compiler, not a
> function of the compiled program. Therefore, slower but more exact functions
> should be preferred, since they only affect the compile time. Note that you
> will only need to do this range propagation on lines that "or" two values
> together, and something that reduces the runtime of the compiler by 216
> seconds, but only when compiling enough code to have over 8 billion 'or'
> operations in it (300^4), I don't think is really that important. Give me
> the exact solution that prevents me from having to cast when the compiler can
> prove it, even if the runtime of the compiler is slightly slower.
>
Funny you should say that given the current thread comparing the
speed of the D compiler to that of the Go compiler...
We are talking about range propagation, a function of the compiler,
not a function of the compiled program. Since we can't get a 100%
accurate representation of the possible values anyway (even yours
might leave holes in the middle after all), then it might be better
to choose a faster, slightly less precise algorithm if the
difference is not too great. That's the difference between a
compiler and a full-fledged static code analysis an program prover.
Anyway, the point is moot, I have a new version of my algorithm
with 100% precision and high speed.
Jerome
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