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Entering a very large number


On 26/03/2018 13:30, Richard Damon wrote:
> On 3/26/18 6:31 AM, bartc wrote:

>> The purpose was to establish how such int("...") conversions compare 
>> in overheads with actual arithmetic with the resulting numbers.
>>
> Of course if this was done in C with a version that had builtin bignum 
> ints or an aggresive enough optimizer (or a Python that did a similar 
> level of optimizations) this function would just test the speed of 
> starting the program, as it actually does nothing and can be optimized 
> away.

Which is a nuisance. /You/ are trying to measure how long it takes to 
perform a task, the compiler is demonstrating how long it takes to /not/ 
perform it! So it can be very unhelpful.

Hence my testing with CPython 3.6, rather than on something like PyPy 
which can give results that are meaningless. Because, for example, real 
code doesn't repeatedly execute the same pointless fragment millions of 
times. But a real context is too complicated to set up.

  Yes, something like this can beused to measure the base time to do
> something, but the real question should be is that time significant 
> compared to the other things that the program is doing, Making a 200x 
> improvement on code that takes 1% of the execution time saves you 
> 0.995%, not normally worth it unless your program is currently running 
> at 100.004% of the allowed (or acceptable) timing, if acceptable timing 
> can even be defined that precisely.

I'm usually concerned with optimisation in a more general sense than a 
specific program.

Such a with a library function (where you don't know how it's going to 
be used); or with a particular byte-code in an interpreter (you don't 
know how often it will be encountered); or a generated code sequence in 
a compiler.

But even 200x improvement on something that takes 1% of the time can be 
worthwhile if it is just one of dozens of such improvements. Sometimes 
these small, incremental changes in performance can add up.

And even if it was just 1%, the aggregate savings across one million 
users of the program can be substantial, even if the individuals won't 
appreciate it. 1% extra battery life might be a handy five minutes for 
example.

-- 
bartc