Mark Brown wrote:
Hi again!
Hey Mark!
While testing my own implementation of lexical cast I discovered that
the stdcxx stringstreams are nearly twice as slow as gcc's. I created
a small test program to convince myself of the difference. On my
x86_64 Linux PC it takes 16 seconds to run through 10 million loops
when using stdcxx but just 9 seconds with gcc. Is there some option or
trick that I don't know about to speed things up? Or maybe a quick fix
that I could work on?
Funny! I get the opposite result with gcc 4.3 in an 8D (shared,
optimized, NOT reentrant) build. Your program runs in 9 seconds
with stdcxx and over 15 seconds with g++. In 12D though, and
with gcc 4.1.2, the results are reversed. In 12D with gcc 4.2,
both programs take 15 seconds.
I think the difference between 8D and 12D is due to the mutex
in stingstream. Even though there's no locking the mutex still
is initialized and that's what I suspect accounts for the slow
runtimes. We need an issue to remind us to fix it as soon as
binary compatibility permits it. As for gcc, I can only guess
that libstdc++ has regressed between 4.1.2 and 4.3.
Martin
Cheers
-- Mark
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <sstream>
#include <typeinfo>
template <class To, class From>
To lex_cast(const From &source)
{
std::stringstream converter;
To dest;
if ((converter << source) && (converter >> dest))
return dest;
throw std::bad_cast();
}
int main(int argc, char *argv[])
{
long loops = atol(argv [1]);
long long sum = 0;
std::string str;
for (long i = 0; i < loops; ++i) {
str = lex_cast<std::string>(i);
sum += str.length();
}
printf("%llu\n", sum);
}
