value range propagation for _bitwise_ OR

"Jérôme M. Berger" jeberger at free.fr
Mon Apr 12 14:09:05 PDT 2010


Steven Schveighoffer wrote:
> On Mon, 12 Apr 2010 13:45:14 -0400, Jérôme M. Berger <jeberger at free.fr>
> wrote:
> 
>>     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.
> 
> When we're talking about the difference between O(1) and O(lgn), I'll
> take accuracy over speed in my compiler any day.  The solution should be
> 100% accurate for the problem statement.  If the problem statement is
> not what we need, then we need a new problem statement :)  Solving the
> problem statement for 99% of values is not good enough.
> 
	And when we're talking about the difference between 10s and 55s for
a minimal loss of accuracy, which will you take? Especially if the
accuracy loss is less than is lost elsewhere (due to holes in the
ranges).

>>
>>     Anyway, the point is moot, I have a new version of my algorithm
>> with 100% precision and high speed.
> 
> Yes, I'm still trying to understand how it works :)
> 
	:)

		Jerome
-- 
mailto:jeberger at free.fr
http://jeberger.free.fr
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