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: template <> const char* std::find(const char* first, const char* last, char value) <const char*> { return ::memchr(first,value,last-first); } Specialisation allows C++ libraries to provide functions that are both generic and optimised for special cases. Anyway, rather than complaining I should be writing code. This week I have been writing some UTF-8 encoding and decoding and Unicode<->iso8859 conversion algorithms. They seem to be faster than the libc implementations which is satisfying especially as I haven't even started on the serious optimisations yet. This will be part of the strings-tagged-with-character-sets stuff that I have described before. Anyone interested? Phil.