Java vs C++ speed (IO & Sorting)

Z

zionztp

No, in that case, we are comparing c++ library vs java library.
Click to expand...

I meant that we are not sure how good are the numbers java/c++
produce, since "more random" numbers usually take more time to
generate, so we would need to know that both C++/Java are producing
equally good numbers before trying to compare speed.

I deleted the code i used to test, i've just rewritten it using
std:string since i was using plain arrays, this one runs 2x slower but
still faster than the original code:

const int len = 50000000;
void randomString(std::string &s)
{
char cr[len];
int n;
unsigned char tn[4];
srand((unsigned)std::time(0));
for( int i = 0 ; i < len; i+=4 ){
n = rand();
memcpy(tn, &n, 4);
s+= (char) (tn[0] % 26 + 97);
s+= (char) (tn[1] % 26 + 97);
s+= (char) (tn[2] % 26 + 97);
s+= (char) (tn[3] % 26 + 97);
}
}

int main()
{
std::string s;
randomString(s);
}

compiled with:
g++ code.cpp -O3

btw could you provide the full java code so i can test both?
 
I

Ian Collins

n = rand();
memcpy(tn, &n, 4);
s+= (char) (tn[0] % 26 + 97);
s+= (char) (tn[1] % 26 + 97);
s+= (char) (tn[2] % 26 + 97);
s+= (char) (tn[3] % 26 + 97);
Click to expand...

Take care, the standard only guarantees RAND_MAX shall be at least
32767. You could end up with rather a lot of 'a'.
 
R

Razii

btw could you provide the full java code so i can test both?
Click to expand...

use server VM and give it 256m
C:\>java -Xmx256m -server Find2


import java.util.*;

public class Find{

public static void main(String[] arg)
{
final int len = 50000000;

long start = System.currentTimeMillis();
String s = randomString(len);
long end = System.currentTimeMillis();
System.out.println("Time: " + (end - start) + " ms");
}

//returns a String of length l with lowercase letters from a to z
static String randomString(int len)
{
char[] cr = new char[len];
Random rd = new Random();
for (int i = 0; i < len; i++){
int num = rd.nextInt(26) + 97;
cr = (char) num;
}

return new String(cr);

}

}
 
R

Razii

const int len = 50000000;
void randomString(std::string &s)
{
char cr[len];
int n;
unsigned char tn[4];
srand((unsigned)std::time(0));
for( int i = 0 ; i < len; i+=4 ){
n = rand();
memcpy(tn, &n, 4);
s+= (char) (tn[0] % 26 + 97);
s+= (char) (tn[1] % 26 + 97);
s+= (char) (tn[2] % 26 + 97);
s+= (char) (tn[3] % 26 + 97);
}
}

int main()
{
std::string s;
randomString(s);
}
Click to expand...

Even this version is slightly slower than java version even without
making changes to the version I posted

C:\>cl /O2 /GL Find.cpp /link /ltcg

Time: 1906 ms (for your version)

I was getting 1700 ms for java version (without changes yet, i will
see if you can do something to make it faster)
 
K

kwikius

btw could you provide the full java code so i can test both?
Click to expand...

use server VM and give it 256m
C:\>java -Xmx256m -server Find2

import java.util.*;

public class Find{

  public static void main(String[] arg)
  {
    final int len = 50000000;

     long start = System.currentTimeMillis();
         String s = randomString(len);
     long end = System.currentTimeMillis();  
         System.out.println("Time: " + (end - start) + " ms");
 }

 //returns a String of length l with lowercase letters from a to z
  static String randomString(int len)
  {
          char[] cr = new char[len];
          Random rd = new Random();
          for (int i = 0; i < len; i++){
             int num =  rd.nextInt(26) + 97;
              cr = (char) num;
         }

     return new String(cr);

  }



}- Hide quoted text -

- Show quoted text -
Click to expand...


What's this shit ?

regards
Andy Little
 
R

Razii

Why don't you address the points in the rest of my post?

Anyway, I must be bored, this should be quicker:
Click to expand...

Yeah, this was quicker BUT IT FAILED THE QUALITY TEST..

The "a" in your string is always more than "z"

C:\>Find a
Number of a: 2333262

C:\>Find z
Number of z: 1794645

C:\>Find z
Number of z: 1794954

C:\>Find a
Number of a: 2336319

You FAILED the requirement. Try again.
 
R

Razii

const int len = 50000000;
void randomString(std::string &s)
{
char cr[len];
int n;
unsigned char tn[4];
srand((unsigned)std::time(0));
for( int i = 0 ; i < len; i+=4 ){
n = rand();
memcpy(tn, &n, 4);
s+= (char) (tn[0] % 26 + 97);
s+= (char) (tn[1] % 26 + 97);
s+= (char) (tn[2] % 26 + 97);
s+= (char) (tn[3] % 26 + 97);
}
}

int main()
{
std::string s;
randomString(s);
}
Click to expand...


Not ONLY your version is still slower than Java, it failed the
quallity test. the 'a's in your version are always more than 'z'

C:\>Find a
Number of a: 25977124
Time: 1875 ms

C:\>Find z
Number of z: 829753
Time: 1921 ms

C:\>Find a
Number of a: 25975915
Time: 1890 ms

C:\>Find z
Number of z: 830666
Time: 1890 ms

FAILURE!!

Compare that with java version

C:\>java -Xmx256m -server Find a
Number of a: 191701
Time: 203 ms

C:\>java -Xmx256m -server Find z
Number of z: 192765
Time: 203 ms

C:\>java -Xmx256m -server Find d
Number of d: 192420
Time: 218 ms

C:\>java -Xmx256m -server Find k
Number of k: 192557
Time: 203 ms

Your version failed the test..
 
R

Razii

Yeah, this was quicker BUT IT FAILED THE QUALITY TEST..
Click to expand...

Your version failed the test. It's not random. There are more 'a's
than 'z's

C:\>Find a
Number of a: 2333262

C:\>Find z
Number of z: 1794645

C:\>Find z
Number of z: 1794954

C:\>Find a
Number of a: 2336319


C:\>java -Xmx256m -server Find d
Number of d: 192420
Time: 218 ms

C:\>java -Xmx256m -server Find k
Number of k: 192557
Time: 203 ms

C:\>java -Xmx256m -server Find a
Number of a: 1923888
Time: 1781 ms

C:\>java -Xmx256m -server Find z
Number of z: 1924369
Time: 1750 ms

C:\>java -Xmx256m -server Find a
Number of a: 1922051
Time: 1813 ms

C:\>java -Xmx256m -server Find z
Number of z: 1923912
Time: 1734 ms
 
Z

zionz

const int len = 50000000;
void randomString(std::string &s)
{
char cr[len];
int n;
unsigned char tn[4];
srand((unsigned)std::time(0));
for( int i = 0 ; i < len; i+=4 ){
n = rand();
memcpy(tn, &n, 4);
s+= (char) (tn[0] % 26 + 97);
s+= (char) (tn[1] % 26 + 97);
s+= (char) (tn[2] % 26 + 97);
s+= (char) (tn[3] % 26 + 97);
}
}
Click to expand...
int main()
{
std::string s;
randomString(s);
}
Click to expand...

Not ONLY your version is still slower than Java, it failed the
quallity test. the 'a's in your version are always more than 'z'

C:\>Find a
Number of a: 25977124
Time: 1875 ms

C:\>Find z
Number of z: 829753
Time: 1921 ms

C:\>Find a
Number of a: 25975915
Time: 1890 ms

C:\>Find z
Number of z: 830666
Time: 1890 ms

FAILURE!!

Compare that with java version

C:\>java -Xmx256m -server Find a
Number of a: 191701
Time: 203 ms

C:\>java -Xmx256m -server Find z
Number of z: 192765
Time: 203 ms

C:\>java -Xmx256m -server Find d
Number of d: 192420
Time: 218 ms

C:\>java -Xmx256m -server Find k
Number of k: 192557
Time: 203 ms

Your version failed the test..
Click to expand...

What??? we are talking about RANDOM numbers, are you sure thats a
valid way of determining randomness?, but maybe the problem is related
to RAND_MAX size, ill take a look at it and see if im getting same
results here.

anyway i just tested with the code you posted, theres some noticeable
difference here:

Java 1650ms avg
C++ 1093ms avg

The C++ time was measured via the 'time' command so it should be a bit
less.
 
R

Razii

C:\>java -Xmx256m -server Find a
Number of a: 191701
Time: 203 ms
Click to expand...

I was using 5 million.. that's why time is 203 ms. With 50 million..

C:\>java -Xmx256m -server Find a
Number of a: 1923974
Time: 1750 ms

C:\>java -Xmx256m -server Find z
Number of z: 1924369
Time: 1750 ms


note how the number of a's and z's are distributed well. Your version
doesn't work.
 
Z

zionz

I was using 5 million.. that's why time is 203 ms. With 50 million..

C:\>java -Xmx256m -server Find a
Number of a: 1923974
Time: 1750 ms

C:\>java -Xmx256m -server Find z
Number of z: 1924369
Time: 1750 ms

note how the number of a's and z's are distributed well. Your version
doesn't work.
Click to expand...

I just tested it here with:

int main()
{
string s;
getRandomString(s);
int i,ac,zc;
ac=zc=0;
for(i=0; i<s.size(); i++){
if(s=='a'){ac++;}
if(s=='z'){zc++;}
}
cout << ac << endl << zc << endl;
}

output:
Results:
1952956
1709172

So its not that bad here...
 
R

Razii

What??? we are talking about RANDOM numbers
Click to expand...

Your version is not random... it has more a's than z's.. also, time
doesn't mater here because your versioon is not working. I can make
java version like you and it will be faster, but what would be point?
Your version is not even working

C:\>Find a
Number of a: 25976908
Time: 1906 ms

C:\>Find z
Number of z: 831122
Time: 1890 ms

C:\>Find a
Number of a: 25976872
Time: 1890 ms

C:\>Find z
Number of z: 828853
Time: 1906 ms

Compare that with mine

C:\>java -Xmx256m -server Find a
Number of a: 1924228
Time: 1765 ms

C:\>java -Xmx256m -server Find z
Number of z: 1923019
Time: 1766 ms

C:\>java -Xmx256m -server Find a
Number of a: 1922127
Time: 1750 ms

C:\>java -Xmx256m -server Find z
Number of z: 1921560
Time: 1954 ms

Also, note time .. your version is slower on my computer and doesn't
even work.
 
R

Razii

I just tested it here with:
Click to expand...

Let me post the whole program so you can test both. You version
doesn't work


=== C++===
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <string>

using namespace std;

const int len = 50000000;
void getRandomString( std::string& s, size_t len);
void randomString( std::string& s);

int main( int argc, char *argv[])
{
if (argc < 2) { cout << "Fool enter text to search"; exit(0);}

string s;

string toSearch = argv[1];

clock_t start=clock();
randomString (s);
//getRandomString(s, len); version by Ian
clock_t endt=clock();

int found = s.find (toSearch);
int count = 0;
while (found!=string::npos)
{
count++;
found=s.find(toSearch,found+1);
}

std::cout <<"Number of " << toSearch << ": " << count << "\n";
std::cout <<"Time: " <<
double(endt-start)/CLOCKS_PER_SEC * 1000 << " ms\n";
}

/*
//my version
void getRandomString( std::string& s, size_t len )
{
srand((unsigned)std::time(0));

std::string cr( len, '\0' );
for( int i = 0 ; i < len ; ++i )
{
int iNumber;
iNumber = rand() % 26 + 97;
cr = (char) iNumber;
}

s.swap( cr );
}

*/

//version by zionz
void randomString(std::string &s)
{
char cr[len];
int n;
unsigned char tn[4];
srand((unsigned)std::time(0));
for( int i = 0 ; i < len; i+=4 ){
n = rand();
memcpy(tn, &n, 4);
s+= (char) (tn[0] % 26 + 97);
s+= (char) (tn[1] % 26 + 97);
s+= (char) (tn[2] % 26 + 97);
s+= (char) (tn[3] % 26 + 97);
}
}


//version by Ian Collins
void getRandomString( std::string& s, size_t len )
{
srand(std::time(0));

std::string cr( len, '\0' );

// The following code is based on the requirement that RAND_MAX
// shall be at least 32767.
//
const size_t byThree = (len/3)*3;

size_t i(0);

while( i < byThree )
{
const int iNumber( rand() );

cr[i++] = iNumber % 26 + 97;
cr[i++] = (iNumber>>5) % 26 + 97;
cr[i++] = (iNumber>>10) % 26 + 97;
}

while( i < len )
{
const int iNumber( rand() );

cr[i++] = iNumber % 26 + 97;
}

s.swap( cr );
}

===Java===

import java.util.*;

public class Find{

public static void main(String[] arg)
{
if (arg == null)
{
System.out.println("Fool! Enter text on command line to search");
System.exit(-1);
}

final int len = 50000000;
String toSearch = arg[0];

//create a string with 50 million chars from a-z

long start = System.currentTimeMillis();
String s = randomString(len);
long end = System.currentTimeMillis();

int count = 0;
int index = s.indexOf(toSearch);
while (index != -1)
{
index++;
count++;
index = s.indexOf(toSearch, index);
}


System.out.println("Number of " + toSearch + ": " + count);
System.out.println("Time: " + (end - start) + " ms");
}

//returns a String of length l with lowercase letters from a to z
static String randomString(int len)
{
char[] cr = new char[len];
Random rd = new Random();
for (int i = 0; i < len; i++){
int num = rd.nextInt(26) + 97;
cr = (char) num;
}

return new String(cr);

}

}
 
T

Tim Smith

I always post the complete thing that people can cut and paste. What's
with posting snippets?

Anyway, his example didn't compile so until he does it, c++ was
slower.
Click to expand...

You code doesn't always compile, either.
 
R

Razii

if (arg == null)
{
System.out.println("Fool! Enter text on command line to search");
System.exit(-1);
}
Click to expand...

Ops, this should be

if (arg.length == 0)
{
System.out.println("Fool! Enter text on command line to search");
System.exit(-1);
}
 
R

Razii

So its not that bad here...
Click to expand...

want to see another proof your version is failure?

WATCH THIS

C:\>Find zion
Number of zion: 0
Time: 1890 ms

C:\>Find zion
Number of zion: 0
Time: 1890 ms

C:\>Find zion
Number of zion: 0
Time: 2062 ms

that's because you have so few z's:

Now watch this:

C:\>java -Xmx256m -server Find zion
Number of zion: 127
Time: 1812 ms

C:\>java -Xmx256m -server Find zion
Number of zion: 121
Time: 1750 ms

C:\>java -Xmx256m -server Find zion
Number of zion: 106
Time: 1797 ms


EVEN YOUR OWN PROGRAM DOESN'T RECOGNIZE YOU

:)
 
Z

zionz

want to see another proof your version is failure?

WATCH THIS

C:\>Find zion
Number of zion: 0
Time: 1890 ms

C:\>Find zion
Number of zion: 0
Time: 1890 ms

C:\>Find zion
Number of zion: 0
Time: 2062 ms

that's because you have so few z's:

Now watch this:

C:\>java -Xmx256m -server Find zion
Number of zion: 127
Time: 1812 ms

C:\>java -Xmx256m -server Find zion
Number of zion: 121
Time: 1750 ms

C:\>java -Xmx256m -server Find zion
Number of zion: 106
Time: 1797 ms

EVEN YOUR OWN PROGRAM DOESN'T RECOGNIZE YOU

:)
Click to expand...

Could you verify this one:

void getRandomString(std::string &s)
{
int n,i;
srand((unsigned)std::time(0));
s.reserve(len);
for(i = 0 ; i < len; i+=4){
n = rand();
s+= (char) (n % 26 + 97);
s+= (char) ( (n>>8) % 26 + 97);
s+= (char) ( (n>>16) % 26 + 97);
s+= (char) ( (n>>24) % 26 + 97);
}
}

btw it seems the c++ rand() is slower than the java equivalent, and in
this test theres no real way of optimizing the things since everything
depends on that function.
 
L

Lew

In my system the rand() function is taking most of the time in this
test, and since it generates a 4 bytes random number i tried the
following:

n = rand();
memcpy(&n, nt, 4);
b[i+0] = nt[0] % 26 + 97;
b[i+1] = nt[1] % 26 + 97;
b[i+2] = nt[2] % 26 + 97;
b[i+3] = nt[3] % 26 + 97;

This resulted into 6x faster execution.
Click to expand...

But not necessarily in equally random bytes.

The trouble is that randomness of each byte is not guaranteed by randomness of
the whole int.
 
R

Razii

Could you verify this one:
Click to expand...

I would but I already posted the sorce so you can also verify it
yourself


=== C++===
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <string>

using namespace std;

const int len = 50000000;
void getRandomString( std::string& s, size_t len);
void randomString( std::string& s);

int main( int argc, char *argv[])
{
if (argc < 2) { cout << "Fool enter text to search"; exit(0);}

string s;

string toSearch = argv[1];

clock_t start=clock();
randomString (s);
//getRandomString(s, len); version by Ian
clock_t endt=clock();

int found = s.find (toSearch);
int count = 0;
while (found!=string::npos)
{
count++;
found=s.find(toSearch,found+1);
}

std::cout <<"Number of " << toSearch << ": " << count << "\n";
std::cout <<"Time: " <<
double(endt-start)/CLOCKS_PER_SEC * 1000 << " ms\n";
}

/*
//my version
void getRandomString( std::string& s, size_t len )
{
srand((unsigned)std::time(0));

std::string cr( len, '\0' );
for( int i = 0 ; i < len ; ++i )
{
int iNumber;
iNumber = rand() % 26 + 97;
cr = (char) iNumber;
}

s.swap( cr );
}

*/

//version by zionz
void randomString(std::string &s)
{
char cr[len];
int n;
unsigned char tn[4];
srand((unsigned)std::time(0));
for( int i = 0 ; i < len; i+=4 ){
n = rand();
memcpy(tn, &n, 4);
s+= (char) (tn[0] % 26 + 97);
s+= (char) (tn[1] % 26 + 97);
s+= (char) (tn[2] % 26 + 97);
s+= (char) (tn[3] % 26 + 97);
}
}


//version by Ian Collins
void getRandomString( std::string& s, size_t len )
{
srand(std::time(0));

std::string cr( len, '\0' );

// The following code is based on the requirement that RAND_MAX
// shall be at least 32767.
//
const size_t byThree = (len/3)*3;

size_t i(0);

while( i < byThree )
{
const int iNumber( rand() );

cr[i++] = iNumber % 26 + 97;
cr[i++] = (iNumber>>5) % 26 + 97;
cr[i++] = (iNumber>>10) % 26 + 97;
}

while( i < len )
{
const int iNumber( rand() );

cr[i++] = iNumber % 26 + 97;
}

s.swap( cr );
}

===Java===

import java.util.*;

public class Find{

public static void main(String[] arg)
{
if (arg.length == 0)
{
System.out.println("Fool! Enter text on command line to search");
System.exit(-1);
}

final int len = 50000000;
String toSearch = arg[0];

//create a string with 50 million chars from a-z

long start = System.currentTimeMillis();
String s = randomString(len);
long end = System.currentTimeMillis();

int count = 0;
int index = s.indexOf(toSearch);
while (index != -1)
{
index++;
count++;
index = s.indexOf(toSearch, index);
}


System.out.println("Number of " + toSearch + ": " + count);
System.out.println("Time: " + (end - start) + " ms");
}

//returns a String of length l with lowercase letters from a to z
static String randomString(int len)
{
char[] cr = new char[len];
Random rd = new Random();
for (int i = 0; i < len; i++){
int num = rd.nextInt(26) + 97;
cr = (char) num;
}

return new String(cr);

}

}
 
R

Razii

Could you verify this one:

void getRandomString(std::string &s)
{
int n,i;
srand((unsigned)std::time(0));
s.reserve(len);
for(i = 0 ; i < len; i+=4){
n = rand();
s+= (char) (n % 26 + 97);
s+= (char) ( (n>>8) % 26 + 97);
s+= (char) ( (n>>16) % 26 + 97);
s+= (char) ( (n>>24) % 26 + 97);
}
}
Click to expand...


Nope...

C:\>Find a
Number of a: 25970426
Time: 1422 ms

C:\>Find z
Number of z: 872062
Time: 1438 ms

C:\>Find zion
Number of zion: 0
Time: 1437 ms

C:\>Find adam
Number of adam: 0
Time: 1421 ms

in java adam returns

C:\>java -Xmx256m -server Find adam
Number of adam: 116
Time: 1766 ms

(notw it's similar number as zion because both words are 4 letters. A
true random string will always return similar number for 4 letter
word).
 

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