.Net 函数调用的性能 (C# F#) VS C++ [英] Performance of .Net function calling (C# F#) VS C++
问题描述
自从 F# 2.0 成为 VS2010 的一部分后，我对 F# 产生了兴趣.我想知道使用它有什么意义.我读了一点，我做了一个基准来衡量函数调用.我用过阿克曼的函数 :)
Since F# 2.0 has become a part of VS2010 I take an interest in F#. I wondered what's the point of using it. I'd read a bit and I made a benchmark to measure functions calling. I have used Ackermann's function :)
C#
sealed class Program
{
public static int ackermann(int m, int n)
{
if (m == 0)
return n + 1;
if (m > 0 && n == 0)
{
return ackermann(m - 1, 1);
}
if (m > 0 && n > 0)
{
return ackermann(m - 1, ackermann(m, n - 1));
}
return 0;
}
static void Main(string[] args)
{
Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();
Console.WriteLine("C# ackermann(3,10) = " + Program.ackermann(3, 10));
stopWatch.Stop();
Console.WriteLine("Time required for execution: " + stopWatch.ElapsedMilliseconds + "ms");
Console.ReadLine();
}
}
C++
class Program{
public:
static inline int ackermann(int m, int n)
{
if(m == 0)
return n + 1;
if (m > 0 && n == 0)
{
return ackermann(m - 1, 1);
}
if (m > 0 && n > 0)
{
return ackermann(m - 1, ackermann(m, n - 1));
}
return 0;
}
};
int _tmain(int argc, _TCHAR* argv[])
{
clock_t start, end;
start = clock();
std::cout << "CPP: ackermann(3,10) = " << Program::ackermann(3, 10) << std::endl;
end = clock();
std::cout << "Time required for execution: " << (end-start) << " ms." << "
";
int i;
std::cin >> i;
return 0;
}
F#
// Ackermann
let rec ackermann m n =
if m = 0 then n + 1
elif m > 0 && n = 0 then ackermann (m - 1) 1
elif m > 0 && n > 0 then ackermann (m - 1) (ackermann m (n - 1))
else 0
open System.Diagnostics;
let stopWatch = Stopwatch.StartNew()
let x = ackermann 3 10
stopWatch.Stop();
printfn "F# ackermann(3,10) = %d" x
printfn "Time required for execution: %f" stopWatch.Elapsed.TotalMilliseconds
Java
public class Main
{
public static int ackermann(int m, int n)
{
if (m==0)
return n + 1;
if (m>0 && n==0)
{
return ackermann(m - 1,1);
}
if (m>0 && n>0)
{
return ackermann(m - 1,ackermann(m,n - 1));
}
return 0;
}
public static void main(String[] args)
{
System.out.println(Main.ackermann(3,10));
}
}
然后
C# = 510 毫秒
C++ = 130 毫秒
F# = 185 毫秒
Java = Stackoverflow :)
An then
C# = 510ms
c++ = 130ms
F# = 185ms
Java = Stackoverflow :)
是否是 F# 的强大功能(除了少量代码)如果我们想使用 .Net 并获得更快的执行速度?我可以优化这些代码中的任何一个吗(尤其是 F#)?
Is it the power of F# (except small amount of code) If we want to use .Net and gain a bit faster execution? Can I optimalize any of these codes (especially F#) ?
更新.我摆脱了 Console.WriteLine 并在没有调试器的情况下运行 C# 代码:C# = 400ms
UPDATE. I got rid off Console.WriteLine and run the C# code without the debugger: C# = 400ms
推荐答案
我相信在这种情况下，C# 和 F# 之间的区别要归功于尾调用优化.
I believe that in this case, the difference between C# and F# is thanks to tail-call optimization.
尾调用是指在函数中作为最后一件事"完成的递归调用.在这种情况下，F#实际上并没有生成调用指令，而是将代码编译成一个循环(因为调用是最后一件事"，我们可以重用当前堆栈帧，直接跳转到方法的开头).
A tail-call is when you have a recursive call that is done as "the last thing" in a function. In this case, F# doesn't actually generate a call instruction, but instead compiles the code into a loop (because the call is the "last thing", we can reuse the current stack frame and just jump to the beginning of the method).
在您的 ackermann 实现中，有两个调用是尾调用，只有一个不是(结果作为参数传递给另一个 ackermann代码>调用).这意味着 F# 版本实际上更少调用调用"指令(很多?).
In your implementation of ackermann, two of the calls are tail-calls and only one of them is not (the one where the result is passed as an argument to another ackermann call). This means that the F# version actually invokes a "call" instruction (much?) less often.
总的来说，性能配置文件与 C# 的性能配置文件大致相同.这里有很多与 F# 与 C# 性能相关的帖子:
In generall, the performance profile is roughly the same as performance profile of C#. There are quite a few posts related to F# vs. C# performance here:
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