在计算素数时，NodeJS 比 D 快。如何？

Question

我在 D 中编写了一个计算素数的简单函数。我认为它非常快，可以计算高达 100,000 的素数。但后来我想将它与 NodeJS 进行比较。当我第一次运行 NodeJS 脚本时，我对差异感到震惊，并仔细检查了我并没有跳过某种计算。但两者在功能上几乎相同。

D:

import std.stdio;
import std.math;
import std.datetime;
import std.file;
import std.array;

enum size_t ITERATIONS = 100_000;

bool divisible(real n) {
    real d;
    for(d = 3; d < floor(n / 2); d += 2) {
        if(n % d == 0) {
            return true;
        }
    }

    return false;
}

void main() {
    StopWatch sw;
    size_t T = ITERATIONS;
    size_t C = 0;
    real n = 2;
    real r[ITERATIONS];
    r[C] = n;
    sw.start();
    C++;
    for(n = 3; n < T; n += 2) {
        if(!divisible(n)) {
            r[C] = n;
            C++;
        }
    }

    sw.stop();
    double seconds = cast(double)sw.peek().usecs / 1_000_000;
    writeln("\n\n", C, " prime numbers calculated in ", seconds, " seconds.");


    File file = File("primes.txt", "w");
    file.writeln("\n", C, " prime numbers calculated ", seconds, " seconds.");

    foreach(number; r[0..C]) {
        file.writeln(number);
    }

    file.writeln("\n", "end");
    file.close();
}

NodeJS：

var fs = require('fs');

var ITERATIONS = 100000;

function divisible(n) {
    var d;
    for(d = 3; d < Math.floor(n / 2); d += 2) {
        if(n % d == 0) {
            return true;
        }
    }

    return false;
}

(function() {
    var buffer  = [ ],
        now     = Date.now(),
        C       = 0
        n       = 2
        ;

    buffer.push(n);
    C++;
    for(n = 3; n < ITERATIONS; n += 2) {
        if(!divisible(n)) {
            buffer.push(n);
            C++;
        }
    }

    var time    = Date.now() - now,
        seconds = time / 1000
        ;

    console.log("\n\n", C, " prime numbers calculated. Process took ", seconds, " seconds.");
    buffer.push("\n" + C + " prime numbers calculated. Process took " + seconds + " seconds.");

    fs.writeFile("node_primes.txt", buffer.join("\n"), function(err) {
        if(err) throw err;

        console.log("Primes have been written to file.");   
    });
})();

结果：

Calculating 100,000 primes:
D:      3.49126 seconds
NodeJS: 0.652 seconds

谁能解释为什么会这样？

提前致谢。

Answer 1

通过将变量不必要地声明为real，您在可以使用整数运算的情况下强制使用浮点运算。将所有real 实例替换为int，去掉floor()，您的D 程序将与Node.JS 版本一样快：

import std.stdio;
import std.math;
import std.datetime;
import std.file;
import std.array;

enum size_t ITERATIONS = 100_000;

bool divisible(int n) {
    int d;
    for(d = 3; d < n / 2; d += 2) {
        if(n % d == 0) {
            return true;
        }
    }

    return false;
}

void main() {
    StopWatch sw;
    size_t T = ITERATIONS;
    size_t C = 0;
    int n = 2;
    int r[ITERATIONS];
    r[C] = n;
    sw.start();
    C++;
    for(n = 3; n < T; n += 2) {
        if(!divisible(n)) {
            r[C] = n;
            C++;
        }
    }

    sw.stop();
    double seconds = cast(double)sw.peek().usecs / 1_000_000;
    writeln("\n\n", C, " prime numbers calculated in ", seconds, " seconds.");


    File file = File("primes.txt", "w");
    file.writeln("\n", C, " prime numbers calculated ", seconds, " seconds.");

    foreach(number; r[0..C]) {
        file.writeln(number);
    }

    file.writeln("\n", "end");
    file.close();
}