Re: [boost] [review] Fast track formal review of Forward library begins today

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2007-12-09 03:38:48

Joel de Guzman wrote:
> Joel wrote:
> 
>>> I'd like to see more tweakable
>>> parameters for specific uses. I frequently deal with
>>> different number expansions in a case to case basis.
>>> For example, is it possible to have arity 3 for function
>>> X and arity-5 for function Y? A single number seems
>>> wasteful if I'm sure that a certain use needs only a few.
>>> Is that possible?
>> Yes, I think so. And it turns out to be a very good idea, as it
>> potentially makes overload resolution *a lot* faster. Here comes the 
>> benchmark compiling do_the_bind.cpp, ported to use the forward adapter 
>> with gcc:
>>
>>    Arity=8
>>    preprocess
>>
>>    real    0m1.384s
>>    user    0m1.270s
>>    sys     0m0.109s
>>
>>    preprocess, compile, link
>>
>>    real    0m12.405s
>>    user    0m11.769s
>>    sys     0m0.540s
>>
>>
>>    Arity=4
>>    preprocess
>>
>>    real    0m0.918s
>>    user    0m0.454s
>>    sys     0m0.081s
>>
>>    preprocess, compile, link
>>
>>    real    0m1.949s
>>    user    0m1.653s
>>    sys     0m0.268s
> 
> Wow that's interesting. Is the trend exponential?
> Can't really tell with just 2 sample points.

Yeah, seems so:

    4 -> 1.4
    5 -> 1.5
    6 -> 2
    7 -> 3
    8 -> 11.2
    (compile & link time only)

And these are just a few calls - we can easily have a higher constant in
practice...

>> Interestingly preprocessing is a minor concern and so we could even 
>> provide means to take our pick at compile time (as opposed to 
>> preprocessing time).
> 
> Not so fast. Don't forget EDG.

No panic, I will also allow fractional preprocessing :-). The idea to
(almost) mostly pay for what one knows to use at compile time (rather 
than what one assumes one might need at preprocessing time) makes 
compile time control a tempting feature to have, however.

Regards,
Tobias