The Computer Language
Benchmarks Game

n-body Swift #5 program

source code

/* The Computer Language Benchmarks Game
 http://benchmarksgame.alioth.debian.org/
 contributed by Isaac Gouy
 modified by TVSori None
 converted to Swift 3 by Sergo Beruashvili
 */

import Glibc
//import Darwin

struct Body {
    var x, y, z, vx, vy, vz, mass : Double
    
    init(x: Double, y: Double, z: Double,
         vx: Double, vy: Double, vz: Double, mass: Double) {
        self.x = x
        self.y = y
        self.z = z
        self.vx = vx
        self.vy = vy
        self.vz = vz
        self.mass = mass
    }
}

let PI = 3.141592653589793
let SOLAR_MASS = 4 * PI * PI
let DAYS_PER_YEAR = 365.24

var bodies: [Body] = [
    Body (
        x: 0.0,
        y: 0.0,
        z: 0.0,
        vx: 0.0,
        vy: 0.0,
        vz: 0.0,
        mass: SOLAR_MASS
    ),
    
    Body (
        x: 4.84143144246472090e+00,
        y: -1.16032004402742839e+00,
        z: -1.03622044471123109e-01,
        vx: 1.66007664274403694e-03 * DAYS_PER_YEAR,
        vy: 7.69901118419740425e-03 * DAYS_PER_YEAR,
        vz: -6.90460016972063023e-05 * DAYS_PER_YEAR,
        mass: 9.54791938424326609e-04 * SOLAR_MASS
    ),
    
    Body (
        x: 8.34336671824457987e+00,
        y: 4.12479856412430479e+00,
        z: -4.03523417114321381e-01,
        vx: -2.76742510726862411e-03 * DAYS_PER_YEAR,
        vy: 4.99852801234917238e-03 * DAYS_PER_YEAR,
        vz: 2.30417297573763929e-05 * DAYS_PER_YEAR,
        mass: 2.85885980666130812e-04 * SOLAR_MASS
    ),
    
    Body (
        x: 1.28943695621391310e+01,
        y: -1.51111514016986312e+01,
        z: -2.23307578892655734e-01,
        vx: 2.96460137564761618e-03 * DAYS_PER_YEAR,
        vy: 2.37847173959480950e-03 * DAYS_PER_YEAR,
        vz: -2.96589568540237556e-05 * DAYS_PER_YEAR,
        mass: 4.36624404335156298e-05 * SOLAR_MASS
    ),
    
    Body (
        x: 1.53796971148509165e+01,
        y: -2.59193146099879641e+01,
        z: 1.79258772950371181e-01,
        vx: 2.68067772490389322e-03 * DAYS_PER_YEAR,
        vy: 1.62824170038242295e-03 * DAYS_PER_YEAR,
        vz: -9.51592254519715870e-05 * DAYS_PER_YEAR,
        mass: 5.15138902046611451e-05 * SOLAR_MASS
    )
]


func offsetMomentum() {
    var px = 0.0
    var py = 0.0
    var pz = 0.0
    
    for body in bodies {
        px += body.vx * body.mass
        py += body.vy * body.mass
        pz += body.vz * body.mass
    }
    
    bodies[0].vx = -px / SOLAR_MASS;
    bodies[0].vy = -py / SOLAR_MASS;
    bodies[0].vz = -pz / SOLAR_MASS;
}


func energy() -> Double {
    var dx, dy, dz, distance: Double
    var e = 0.0
    let arrPtr = UnsafeMutablePointer<Body>(mutating: bodies)
    for i in 0..<bodies.count {
        e += 0.5 * arrPtr[i].mass *
            ( arrPtr[i].vx * arrPtr[i].vx
                + arrPtr[i].vy * arrPtr[i].vy
                + arrPtr[i].vz * arrPtr[i].vz )
        
        for j in i+1..<bodies.count {
            dx = arrPtr[i].x - arrPtr[j].x
            dy = arrPtr[i].y - arrPtr[j].y
            dz = arrPtr[i].z - arrPtr[j].z
            
            distance = sqrt(dx*dx + dy*dy + dz*dz)
            e -= (arrPtr[i].mass * arrPtr[j].mass) / distance
        }
    }
    return e;
}


func advance(_ dt: Double) {
    var dx, dy, dz, distance, mag: Double
    let arrPtr = UnsafeMutablePointer<Body>(mutating: bodies)
    for i in 0..<bodies.count {
        for j in i+1..<bodies.count {
            dx = arrPtr[i].x - arrPtr[j].x
            dy = arrPtr[i].y - arrPtr[j].y
            dz = arrPtr[i].z - arrPtr[j].z
            
            distance = sqrt(dx*dx + dy*dy + dz*dz)
            mag = dt / (distance * distance * distance)
            
            arrPtr[i].vx -= dx * arrPtr[j].mass * mag
            arrPtr[i].vy -= dy * arrPtr[j].mass * mag
            arrPtr[i].vz -= dz * arrPtr[j].mass * mag
            
            arrPtr[j].vx += dx * arrPtr[i].mass * mag
            arrPtr[j].vy += dy * arrPtr[i].mass * mag
            arrPtr[j].vz += dz * arrPtr[i].mass * mag
        }
    }
    
    for i in 0..<bodies.count {
        arrPtr[i].x += dt * arrPtr[i].vx
        arrPtr[i].y += dt * arrPtr[i].vy
        arrPtr[i].z += dt * arrPtr[i].vz
    }	
}


let n: Int = Int(CommandLine.arguments[1])!
offsetMomentum()
print( energy() )
for _ in 1...n {
    advance(0.01)
}
print( energy() )
    

notes, command-line, and program output

NOTES:
64-bit Ubuntu quad core
Swift version 3.1-dev (LLVM a7c680da51, Clang 9772bf511a, Swift cf5f914377)
Target: x86_64-unknown-linux-gnu
swift-3.1-DEVELOPMENT-SNAPSHOT-2017-03-23-a-ubuntu16.04



Fri, 24 Mar 2017 18:12:54 GMT

MAKE:
/usr/local/src/swift-3.1-DEVELOPMENT-SNAPSHOT-2017-03-23-a-ubuntu16.04/usr/bin/swiftc nbody.swift-5.swift -Ounchecked -whole-module-optimization  -o nbody.swift-5.swift_run
1.05s to complete and log all make actions

COMMAND LINE:
./nbody.swift-5.swift_run 50000000

PROGRAM OUTPUT:
-0.169075163828524
-0.169059906802725