Re: [boost] [xpressive] Performance Tuning?

Subject: Re: [boost] [xpressive] Performance Tuning?
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2009-07-19 10:14:10

> > I just changed the file to use spirit for parsing where I had used
> > lexical_cast got very different timings for xpressive now, so now,
> > with xpressive using a bit of spirit I get:
> > Loop count:  10000000
> > Parsing:  42.5
> > xpressive:  15.4841
> > spirit-quick(static):  3.01117
> > spirit-quick_new(threadsafe):  3.10548
> > spirit-grammar(threadsafe/reusable):  3.81694
> >
> > Vast increase, 3x faster xpressive is now.
> > Also, how do you fix that rather bloody massive warning about
> > double->int64 truncation?
> > I also changed all int64_t to boost::long_long_type since they are
> the
> > same thing anyway (on 32-bit at least?), as well as it being
> > multi-platform unlike int64_t.
> > My changed file is attached.  Do not know if this is considered
> > cheating now that xpressive is using some spirit now.  ;-)
> 
> This is somewhat cheating. We've tuned the numeric parsers of Spirit
> with TMP tricks, loop unrolling, etc. Those are very finely tuned
> numeric parsers you see there that beats the fastest C code such as
> strtol and atoi. The following benchmarks reveal 2X+ speed against low
> level strtol and atoi (attached). I am getting:
> 
>    atoi: 0.82528 [s]
>    strtol: 0.792227 [s]
>    int_: 0.358016 [s]
> 
> The first and second are the low-level C routines. The third is
> Spirit's int_ parser. I need not mention that the C routines only
> accept C strings while the Spirit int_ parser can accept any forward
> iterator. So, in a sense, we're comparing apples and oranges. But this
> goes to show that you can write highly optimized code in generic C++.

Slightly off-topic, but in order to emphasize what Joel said, here are a
couple of benchmark results I published a couple of days ago related to
output formatting: http://tinyurl.com/n4368t. Just an excerpt (Intel Core
Duo(tm) Processor, 2.8GHz, 4GByte RAM, Intel 11.1/64Bit):

Performance comparison for formatting a single double (all times in [s],
1000000 iterations):
sprintf: 0.694
iostreams: 1.354
Boost.Format: 2.011
Karma double_: 0.218

(where double_ is the Spirit.Karma output generator for a default floating
point format)

Regards Hartmut