Node.js与C ++的性能实现简单数学

Question

I made the same program to test performance on Nodejs and C++ on Mac OS X.

First in C++:

#include <iostream>
#include <time.h>

using namespace std;

int main() {
    clock_t t1, t2;

    cout << "Initializing\n";

    t1 = clock();

    double m = 0;
    for (double i = 0; i != 10000000000; ++i) {
        m = i * -1 + i;
    }

    t2 = clock();
    float diff = (((float) t2 - (float) t1) / 1000000.0F) * 1000;

    cout << "Finalizing with " << diff << "ms\n";
}

Second in Nodejs:

console.log("Initializing");

t1 = Date.now();

var m = 0;

for (var i = 0; i != 10000000000; i++) {
    m = i * -1 + i;
}

t2 = Date.now();
var diff = t2 - t1;
console.log("Finalizing with %dms", diff);

The result was 50000ms for C++ and 22000 for Nodejs.

Why Nodejs is faster for that kind of operation?

Thanks.

UPDATE:

Switching double and using long int, it gave me 22000ms, like Nodejs.

Answer 1

The problem is that the code for 2 languages is not equivalent. In C++ you used double and in javascript variable was optimized to be integers (although their type is Number which in general case is floating-point type). And, of course, floating point operations are always longer than operations on integers.

Try to replace double with int or better with long in the C++ version. This will ensure you have integers in both versions.

If you do that please consider posting results for us to see the difference. T

Answer 2

It is quite difficult to measure performance straight off using this type of code. Both the C++ compiler and the V8 JITter uses different types of optimization of the generated native code.

A few things to look out for:

• The code i != 10000000000 is dangerous. Always compare doubles using inequalities ( <> ) rather than equalities ( == , != ).
• There is no need to use floating point at all, use the long long type instead. The thing is, NodeJS may actually do this optimization automatically, since it is dynamically typed.
• You don't actually use m anywhere. If you compile with g++ -O3 , the compiler may actually optimize away the whole loop (try it!).