Comments for A howl on the wind...

Comment on C++ Convert Int to String Speed by Tino Didriksen

Tino Didriksen — Tue, 17 Apr 2012 21:03:45 +0000

It’s already shown in the post where it says “Source for the test is at speed-convert-int-to-string.cpp with cycle.h.”
( http://tinodidriksen.com/uploads/code/cpp/speed-convert-int-to-string.cpp + http://tinodidriksen.com/uploads/code/cpp/cycle.h )

Comment on C++ Convert Int to String Speed by Joe

Joe — Tue, 17 Apr 2012 20:55:03 +0000

Hi, can you show source code, on which you tested speed of conversion from int to string?

Comment on Snippet: Vector to Output Stream by Pierre

Pierre — Mon, 19 Mar 2012 10:59:41 +0000

copy(vec.begin(), vec.end(), ostream_iterator(std::cout,”,”);

Work as good as you ask. (You have to add the “[" and "]” manually).

Comment on C++ String Compare Performance by Rodrigo

Rodrigo — Thu, 22 Sep 2011 00:51:15 +0000

I personally dislike not only the operator== overloading, but the C++ operator overloading in general. To me they hide way too much what is being done, and it’s easy to neglect optimizations.

Comment on C++ String Compare Performance by Tino Didriksen

Tino Didriksen — Wed, 14 Sep 2011 08:50:49 +0000

Well, I am not very happy with this test. I can reliably reproduce the results, but the results are not what I would expect.

string op== is horrendous. There is no way in my head that a sane implementation of that should be slower than strcmp(), yet it is. And the fact that it’s even slower when comparing to char* tells me they just let the buffer get silently converted to a string, then compare…which is crazy (but it is standard compliant).

Comment on C++ String Compare Performance by Ayyappa

Ayyappa — Tue, 13 Sep 2011 17:51:09 +0000

Hai,

Recently I also done an performance test on the same aspect.But your Performance check range(based on different envi) is relatively high.Can you please finalize the results in brief synopsis.(something like strcmp()-> which might use memcmp func is faster…).Please finalize a summary on this test.

Comment on C++ Include Speed by Tino Didriksen

Tino Didriksen — Thu, 01 Sep 2011 19:51:59 +0000

I thought of that, so I tested it on a real machine and got same relative results. And I did run every compilation 5-7 times to make sure the files were well cached.

Anyway, the conclusion is that it doesn’t matter. If the difference for 10000 almost empty files is a second or two more, then your real world project won’t care whatsoever which include method you use.

Comment on C++ Include Speed by Nick Porcino

Nick Porcino — Thu, 01 Sep 2011 19:35:25 +0000

Is it possible that file caching or other VM behaviors by VirtualBox is skewing the results from gcc and clang?

Comment on C++ Convert String to Double Speed by Piotr

Piotr — Tue, 02 Aug 2011 11:11:49 +0000

Try this one (not mine, but works):
http://www.leapsecond.com/tools/fast_atof.c

It’s a replacement for atof() – much faster.

Comment on C++ Convert String to Int Speed by phax

phax — Thu, 14 Jul 2011 14:06:49 +0000

Another naive() in asm though, only tested on Linux g++ 4.4.3, not sure if VC++ supports this semantics for inlining asm.

long long int __inline__ naive2(const char * p)
{
int result(0);
int neg(0);

// result -> ecx, p -> ebx
asm (
“movl %0, %%ecx\t\n”
“movl %2, %%ebx\t\n”
“movl $0, %%edx\t\n”
“movb (%%ebx),%%dl\t\n”
“subb $45, %%dl\t\n”
“jnz loop1\t\n”
“movl $1, %1\t\n”
“incl %%ebx\t\n”
“loop1:\t\n”
“movl $0, %%edx\t\n”
“movb (%%ebx), %%dl\t\n”
“testb %%dl,%%dl\t\n”
“jz exitloop1\t\n”
“subb $48, %%dl\t\n”
“movl %%ecx, %%eax\t\n”
“shll $3,%%ecx\t\n”
“addl %%eax, %%ecx\t\n”
“addl %%eax, %%ecx\t\n”
“addl %%edx,%%ecx\t\n”
“incl %%ebx\t\n”
“jmp loop1\t\n”
“exitloop1:\t\n”
“movl %%ecx, %0\t\n”
:
“=r” (result), “=m” (neg)
:
“r”(p),”0″(result), “m” (neg)
: “%ebx”, “%eax”, “%ecx”, “%edx”
);
return neg?-result:result;
}