Florent Clairambault

I found out that there is a much better test than the one i did here. In fact the main interest of the post is this spreadsheet :

I recently did a simple and stupid comparison test between C++ (g++) and C# .Net (mono).

My point here is that C# can actually be considered as a very fast language. It allows automatic hardware-specific optimization.
Lot of people think it’s like a java, it has a virtual machine. But in fact it just compiles everything into native language when it accesses methods. This is the whole purpose of the JIT (Just Int Time compiler).

If you feel the JIT compiler is a possible reason of slowness (it slows down the program startup), you can pre-compile your assemblys (mono –aot on linux). If you feel the mono files are a drawback, you can bundle everything in one file using mkbundle. You can read more about this here.

The only real drawback you have in the .Net framework is the garbage collector. It prevents the C# .Net it from being a realtime language/framework. But in real life usage it doesn’t slow much.

The purpose of the following test is to show that C++ isn’t faster than C# “as is”. I KNOW C# can not be faster than C++ because C# can do few hardware specific optimizations when you can do all of them in C++.

But if you’re searching for arguments to choose C# .Net over native C++, you should also consider these :

• C# is much more simple. No headers, the languages specifications are simple and clear
• You don’t have to manage the memory in .Net (no memory leak, optimal memory consumption, etc.)
• .Net don’t just crash, they always throw an exception and they only crash if nobody catches it
• Mono (and presumely the .Net framework) does some really interesting optimizations :

  1	# mono --list-opt

  I put some link so that you can learn about these really interesting optimization. This is like design patterns, you should really know these things.

  peephole	Peephole postpass
  branch	Branch optimizations
  inline	Inline method calls
  cfold	Constant folding
  consprop	Constant propagation
  copyprop	Copy propagation
  deadce	Dead code elimination
  linears	Linear scan global reg allocation
  cmov	Conditional moves
  shared	Emit per-domain code
  sched	Instruction scheduling
  intrins	Intrinsic method implementations
  tailc	Tail recursion and tail calls
  loop	Loop related optimizations
  fcmov	Fast x86 FP compares
  leaf	Leaf procedures optimizations
  aot	Usage of Ahead Of Time compiled code
  precomp	Precompile all methods before executing Main
  abcrem	Array bound checks removal
  ssapre	SSA based Partial Redundancy Elimination
  exception	Optimize exception catch blocks
  ssa	Use plain SSA form
  treeprop	Tree propagation
  sse2	SSE2 instructions on x86
  gshared	Share generics
  simd	Simd intrinsics

• Multithreading in .net is much easier than any other language. You even have the parrallel loop operations, like Parallel.For.

SO ! Here is the test…

I wrote these two sample programs :

One in C++ :

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

#include <iostream>
using namespace std;
 
long stupidThing( long nb ) {
	long out = 1;
	while( nb > 0 )
		out *= nb--;
 
 
	return out;
}
 
int main() {
 
	long total = 0;
 
	for( int i = 0; i < 1000000; ++i )
		for( long l = 0; l < 100; ++l )
			total += stupidThing( l );
 
	cout << "Total : " << total << endl;
 
	return 0;
}

One in C# :

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

using System;
 
namespace test {
        class Program {
                static long stupidThing( long nb ) {
                        long ret = 1;
                        while ( nb > 0 )
                                ret *= nb--;
                        return ret;
                }
 
                static void Main( string[] args ) {
 
                        long total = 0;
 
                        for ( int i = 0; i < 1000000; ++i )
                                for ( long l = 0; l < 100; ++l )
                                        total += stupidThing( l );
                        Console.WriteLine( "Total : {0}", total );
                }
        }
}

First of all, I open a shell in real-time priority, because I don’t want my other processses to mess with my tests :

1

# rtprio 99 bash

Then I compile the two programs :

1
2

# gmcs test.cs
# g++ -O4 test.cpp -o test

And then I launch my test :

On a 64 bits host :

1

Kernel : 2.6.9-023stab051.3-smp #1 SMP Wed Nov 4 18:36:34 MSK 2009 x86_64 x86_64 x86_64 GNU/Linux

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31

# time ./test ; time ./test ; time ./test ; time mono test.exe ; time mono test.exe ; time mono test.exe
Total : -6192109806162068864
 
real    0m12.433s
user    0m12.394s
sys     0m0.049s
Total : -6192109806162068864
 
real    0m12.415s
user    0m12.411s
sys     0m0.014s
Total : -6192109806162068864
 
real    0m12.430s
user    0m12.411s
sys     0m0.026s
Total : -6192109806162068864
 
real    0m10.311s
user    0m10.287s
sys     0m0.029s
Total : -6192109806162068864
 
real    0m10.254s
user    0m10.247s
sys     0m0.011s
Total : -6192109806162068864
 
real    0m10.250s
user    0m10.255s
sys     0m0.012s

C# clearly beats C++ here. Well

On a 32 bits host :

1

Kernel : 2.6.30-2-686 #1 SMP Fri Dec 4 00:53:20 UTC 2009 i686 GNU/Linux

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31

# time ./test ; time ./test ; time ./test ; time mono test.exe ; time mono test.exe ; time mono test.exe
Total : 100461056
 
real    1m10.927s
user    1m7.376s
sys     0m0.056s
Total : 100461056
 
real    1m12.590s
user    1m8.976s
sys     0m0.020s
Total : 100461056
 
real    1m13.279s
user    1m9.532s
sys     0m0.056s
Total : -6192109806162068864
 
real    2m22.492s
user    2m15.260s
sys     0m0.136s
Total : -6192109806162068864
 
real    2m23.002s
user    2m15.760s
sys     0m0.104s
Total : -6192109806162068864
 
real    2m25.102s
user    2m17.709s
sys     0m0.144s

C++ beats C# here, but in 32 bits C++ use other types whereas C# use the same. In C# long is always 64 bits, in C++ it can be 64 bits or 32 bits (depending on the current architecture).