编程语言EF速度测试(2)：n-body

这是一个专门的编程语言/编译器速度测试/对比网站（http://shootout.alioth.debian.org/）给出的题目，

以下是EF源代码：

import 工具;

//n-body
public final class 启动类 <作者 = "liigo">
{
	public static main() {
		int n = 20000000;

		int time = 运行环境.取启动时间();
		NBodySystem bodies = new NBodySystem();
		控制台.输出行(bodies.energy());
		for (int i=0; i<n; i++)
			bodies.advance(0.01);
		控制台.输出行(bodies.energy());
		控制台.输出行("time(ms): ", 运行环境.取启动时间() - time);
		控制台.输入文本();
	}
}

final class NBodySystem {
	private Body[] bodies;

	public init(){
		bodies = new Body[5];
		bodies[0] = Body.sun();
		bodies[1] = Body.jupiter();
		bodies[2] = Body.saturn();
		bodies[3] = Body.uranus();
		bodies[4] = Body.neptune();

		double px = 0.0;
		double py = 0.0;
		double pz = 0.0;
		for(int i=0; i < bodies.长度; i++) {
			px += bodies[i].vx * bodies[i].mass;
			py += bodies[i].vy * bodies[i].mass;
			pz += bodies[i].vz * bodies[i].mass;
		}
		bodies[0].offsetMomentum(px,py,pz);
	}

	public advance(double dt) {

		for(int i=0; i < bodies.长度; i++) {
			Body iBody = bodies[i];
			for(int j=i+1; j < bodies.长度; j++) {
				double dx = iBody.x - bodies[j].x;
				double dy = iBody.y - bodies[j].y;
				double dz = iBody.z - bodies[j].z;

				double dSquared = dx * dx + dy * dy + dz * dz;
				double distance = 数学运算.求平方根(dSquared);
				double mag = dt / (dSquared * distance);

				iBody.vx -= dx * bodies[j].mass * mag;
				iBody.vy -= dy * bodies[j].mass * mag;
				iBody.vz -= dz * bodies[j].mass * mag;

				bodies[j].vx += dx * iBody.mass * mag;
				bodies[j].vy += dy * iBody.mass * mag;
				bodies[j].vz += dz * iBody.mass * mag;
			}
		}

		foreach (bodies,  Body body) {
			body.x += dt * body.vx;
			body.y += dt * body.vy;
			body.z += dt * body.vz;
		}
	}

	public double energy(){
		double dx, dy, dz, distance;
		double e = 0.0;

		for (int i=0; i < bodies.长度; i++) {
			Body iBody = bodies[i];
			e += 0.5 * iBody.mass *
				( iBody.vx * iBody.vx
				+ iBody.vy * iBody.vy
				+ iBody.vz * iBody.vz );

			for (int j=i+1; j < bodies.长度; j++) {
				Body jBody = bodies[j];
				dx = iBody.x - jBody.x;
				dy = iBody.y - jBody.y;
				dz = iBody.z - jBody.z;

				distance = 数学运算.求平方根(dx*dx + dy*dy + dz*dz);
				e -= (iBody.mass * jBody.mass) / distance;
			}
		}
		return e;
	}
}

final class Body {
	const double PI = 3.141592653589793;
	const double SOLAR_MASS = 4 * PI * PI;
	const double DAYS_PER_YEAR = 365.24;

	public double x, y, z, vx, vy, vz, mass;

	public init(){}

	public static Body jupiter(){
		Body p = new Body();
		p.x = 4.84143144246472090e+00;
		p.y = -1.16032004402742839e+00;
		p.z = -1.03622044471123109e-01;
		p.vx = 1.66007664274403694e-03 * DAYS_PER_YEAR;
		p.vy = 7.69901118419740425e-03 * DAYS_PER_YEAR;
		p.vz = -6.90460016972063023e-05 * DAYS_PER_YEAR;
		p.mass = 9.54791938424326609e-04 * SOLAR_MASS;
		return p;
	}

	public static Body saturn(){
		Body p = new Body();
		p.x = 8.34336671824457987e+00;
		p.y = 4.12479856412430479e+00;
		p.z = -4.03523417114321381e-01;
		p.vx = -2.76742510726862411e-03 * DAYS_PER_YEAR;
		p.vy = 4.99852801234917238e-03 * DAYS_PER_YEAR;
		p.vz = 2.30417297573763929e-05 * DAYS_PER_YEAR;
		p.mass = 2.85885980666130812e-04 * SOLAR_MASS;
		return p;
	}

	public static Body uranus(){
		Body p = new Body();
		p.x = 1.28943695621391310e+01;
		p.y = -1.51111514016986312e+01;
		p.z = -2.23307578892655734e-01;
		p.vx = 2.96460137564761618e-03 * DAYS_PER_YEAR;
		p.vy = 2.37847173959480950e-03 * DAYS_PER_YEAR;
		p.vz = -2.96589568540237556e-05 * DAYS_PER_YEAR;
		p.mass = 4.36624404335156298e-05 * SOLAR_MASS;
		return p;
	}

	public static Body neptune(){
		Body p = new Body();
		p.x = 1.53796971148509165e+01;
		p.y = -2.59193146099879641e+01;
		p.z = 1.79258772950371181e-01;
		p.vx = 2.68067772490389322e-03 * DAYS_PER_YEAR;
		p.vy = 1.62824170038242295e-03 * DAYS_PER_YEAR;
		p.vz = -9.51592254519715870e-05 * DAYS_PER_YEAR;
		p.mass = 5.15138902046611451e-05 * SOLAR_MASS;
		return p;
	}

	public static Body sun(){
		Body p = new Body();
		p.mass = SOLAR_MASS;
		return p;
	}

	public Body offsetMomentum(double px, double py, double pz){
		vx = -px / SOLAR_MASS;
		vy = -py / SOLAR_MASS;
		vz = -pz / SOLAR_MASS;
		return this;
	}
}

这个EF程序，在我的机器上，运行耗时约165 秒。相应的VC6最佳优化后运行耗时约15 秒。

其它编程语言/编译器的表现，请看这里：http://shootout.alioth.debian.org/gp4/benchmark.php?test=nbody&lang=all

总的来说，EF表现不坏。比不少编程语言（如C++, JAVA, C#, D, Fortran, Pascal）慢很多，又比另外不少编程语言（如Erlang, Python, Ruby, Perl, PHP, Lua, Groovy, SmallTalk, JavaScript）快很多。

进一步分析的话：EF作为编译型语言，通常比其它编译型语言都慢（毕竟EF编译器尚未优化），最多慢10倍以上；EF通常比解释型语言都要快，往往快数倍、数十倍，以至上百倍。

还有很多测试题目，有时间再继续。想了解EF语言，请到EF官方博客：http://blog.csdn.net/efdev/