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Julek
Guest
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 Posted: Fri Apr 06, 2007 3:05 pm Post subject: Extremely slow string functions |
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Hello,
take a look at this program:
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <string.h>
#include <time.h>
int WezR()
{
return (int)rand()*(int)rand()+(int)rand();
}
int main(int argc, char* argv[])
{
time_t TimeX,TimeX2;
time(&TimeX);
int D=10000000;
char *TTT=new char[D];
for(int a=0;a<D-1;++a)
TTT[a]='a';
for(int a=0;a<1000000;++a)
TTT[WezR()%(D-1)]='b';
TTT[D-1]=0;
time(&TimeX2);
printf("Preparation - %d\n",TimeX2-TimeX);
for(int a=0;a<1000;++a)
{
int NumerStart=WezR()%(D-1);
char *Start=TTT+NumerStart;
char *Stop=strstr(Start,"aba");
int Dl=(int)Stop-(int)Start;
int f=555;
}
time(&TimeX);
printf("Finding - %d\n",TimeX-TimeX2);
return 0;
}
It creates a large table. 90% of chars are 'a', 10% are 'b', in random
places.
Last "for" finds random place in this string, and looks for the next "aba"
occurence - usually it is about 10 chars from the starting point.
When I compile it with Visual Studio 2005, it shows:
Preparation - 0 or 1
Finding - 0
Even, when I change in the last "for" - 1000 to 10000, finding is still 0
seconds.
In C++ Builder, when I create new console project and run this program, it
shows:
Preparation - 2
Finding - 14
So strstr in C++ Builder is more than 200 times slower in this case. I
think, that C++ Builder is so slow, because this string is so large.
My Turbo C++ is "a little broken" - when I create new console project, I
can't link it - it shows "unresolved externals" about CodeGuard files. I
have to enable CG in project options. In release, program is slow too.
What is the reason? Do you have similar problem? |
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Eelke
Guest
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| Posted: Fri Apr 06, 2007 5:16 pm Post subject: Re: Extremely slow string functions |
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| Quote: | So strstr in C++ Builder is more than 200 times slower in this case. I
think, that C++ Builder is so slow, because this string is so large.
My Turbo C++ is "a little broken" - when I create new console project, I
can't link it - it shows "unresolved externals" about CodeGuard files. I
have to enable CG in project options. In release, program is slow too.
What is the reason? Do you have similar problem?
The reason is CodeGaurd. Codegaurd checks all your memory accesses which |
is slowing down the program. Try to get it to link without codeguard.
Eelke |
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Thomas Maeder [TeamB]
Guest
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| Posted: Fri Apr 06, 2007 6:59 pm Post subject: Re: Extremely slow string functions |
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"Julek" <julekmen (AT) go2 (DOT) pl> writes:
| Quote: | take a look at this program:
#include <stdio.h
#include <stdlib.h
#include <limits.h
#include <string.h
#include <time.h
int WezR()
{
return (int)rand()*(int)rand()+(int)rand();
|
The return type of rand() already is int. Why the casts?
More importantly, the expression may overflow, in which case your
program has undefined behavior.
In particular, WezR() may very well return a negative value ...
| Quote: | }
int main(int argc, char* argv[])
{
time_t TimeX,TimeX2;
time(&TimeX);
int D=10000000;
char *TTT=new char[D];
for(int a=0;a<D-1;++a)
TTT[a]='a';
for(int a=0;a<1000000;++a)
|
[make D const and change 1000000 to D/10, to err on the safe side]
| Quote: | TTT[WezR()%(D-1)]='b';
|
.... and applying % doesn't make it non-negative; more undefined
behavior ...
| Quote: | TTT[D-1]=0;
time(&TimeX2);
printf("Preparation - %d\n",TimeX2-TimeX);
for(int a=0;a<1000;++a)
{
int NumerStart=WezR()%(D-1);
char *Start=TTT+NumerStart;
|
.... and more here. This is where I stopped looking.
Try fixing your program and report back. |
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Minas
Guest
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| Posted: Fri Apr 06, 2007 7:08 pm Post subject: Re: Extremely slow string functions |
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"Julek" <julekmen (AT) go2 (DOT) pl> wrote in msg
news:46161b72 (AT) newsgroups (DOT) borland.com...
| Quote: | int D=10000000;
char *TTT=new char[D];
|
You have to delete array TTT
delete[] TTT;
I got
Preparation -0 or 1
finding - 0
_minas
------
"Only the virtue's conquests have certainty" Sofokleous Erephyle |
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Bob Gonder
Guest
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| Posted: Fri Apr 06, 2007 7:56 pm Post subject: Re: Extremely slow string functions |
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Thomas Maeder [TeamB] wrote:
| Quote: | #include <stdlib.h
return (int)rand()*(int)rand()+(int)rand();
More importantly, the expression may overflow, in which case your
program has undefined behavior.
|
Ummm, I think the maximum calculated value is 3FFF 8000, which is
positive, and doesn't overflow unless int is 16bit.
Replace rand() with RAND_MAX and you get
RAND_MAX * RAND_MAX + RAND_MAX
For easier manual calculation:
RAND_MAX * (RAND_MAX+1)
7FFF * 8000 = 3FFF8000
Perhaps you were thinking of _lrand which returns a 31 bit value. |
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Koen
Guest
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| Posted: Fri Apr 06, 2007 8:00 pm Post subject: Re: Extremely slow string functions |
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It must be the CodeGuard, my output of the program is,
even when I change the last for-loop to 100000 iterations:
Preparation - 0
Finding - 0 |
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Thomas Maeder [TeamB]
Guest
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| Posted: Fri Apr 06, 2007 9:12 pm Post subject: Re: Extremely slow string functions |
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Bob Gonder <notbg (AT) notmindspring (DOT) invalid> writes:
| Quote: | Thomas Maeder [TeamB] wrote:
#include <stdlib.h
return (int)rand()*(int)rand()+(int)rand();
More importantly, the expression may overflow, in which case your
program has undefined behavior.
Ummm, I think the maximum calculated value is 3FFF 8000, which is
positive, and doesn't overflow unless int is 16bit.
|
RAND_MAX is an implementation-defined value. The Standard doesn't
guarantee that the quoted expression doesn't overflow. |
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Julek
Guest
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| Posted: Sat Apr 07, 2007 2:28 am Post subject: Re: Extremely slow string functions |
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Użytkownik "Koen" <koen (AT) ha (DOT) com> napisał w wiadomości
news:Xns990AA2E742888koenhacom (AT) 207 (DOT) 105.83.66...
| Quote: | It must be the CodeGuard,
|
Yes, it's the real reason :)Thank you. |
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