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-bodypublic 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;bodies = Body.sun();bodies = Body.jupiter();bodies = Body.saturn();bodies = Body.uranus();bodies = 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.vx * bodies.mass;py += bodies.vy * bodies.mass;pz += bodies.vz * bodies.mass;}bodies.offsetMomentum(px,py,pz);}public advance(double dt) {for(int i=0; i < bodies.长度; i++) {Body iBody = bodies;for(int j=i+1; j < bodies.长度; j++) {double dx = iBody.x - bodies.x;double dy = iBody.y - bodies.y;double dz = iBody.z - bodies.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.mass * mag;iBody.vy -= dy * bodies.mass * mag;iBody.vz -= dz * bodies.mass * mag;bodies.vx += dx * iBody.mass * mag;bodies.vy += dy * iBody.mass * mag;bodies.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;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;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/
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