On Fri, Feb 15, 2008 at 6:54 PM, Phil Endecott <spam_from_boost_dev@chezphil.org> wrote:
Giovanni Piero Deretta wrote:
On Thu, Feb 14, 2008 at 6:50 PM, Phil Endecott <spam_from_boost_dev@chezphil.org> 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