Re: [boost] [String algorithm] is_any_of has inefficient implementation

From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2008-02-15 13:01:09

On Fri, Feb 15, 2008 at 6:54 PM, Phil Endecott
<spam_from_boost_dev_at_[hidden]> wrote:
> Giovanni Piero Deretta wrote:
>  > On Thu, Feb 14, 2008 at 6:50 PM, Phil Endecott
>  > <spam_from_boost_dev_at_[hidden]> wrote:
>
> >>  In each case, I've used the predicate with std::find_if.  But if I
>  >>  instead use C's strcspn() to do the whole job, I see a relative
>  >>  performance for this example of 20.  I find it depressing that the C++
>  >>  code doesn't come close to that.
>  >
>  > Well, it is not really a fair comparison, the 'C' function is likely
>  > implemented in hand optimized assembler, (http://tinyurl.com/yv8s7g)
>  > and for such a small function, humans are still better than compilers.
>  >  So it isn't really C++ versus C. Also the C version is not generic at
>  > all.
>
>  Hi Giovanni,
>
>  I can't agree with that.  There's no reason why the C++ implementation
>  couldn't be written in hand-optimised assembler too.  Or it could
>  simply call the fast C function:

Actually we are in agreement :). Of course the C++ version (or
specializations of that) can be implemented in hand tuned assembler, I
was just pointing out that the difference in speed wasn't due to
language 'power', but just implementation details. There is no reason
that the C++ interface to be slower to the C one (in fact you have
shown that, by using compile time knowledge, a plain C++ version can
even beat the assembler code).

-- 
gpd