source code
/* The Computer Language Benchmarks Game
https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
contributed by Ralph Ganszky
Added dummy element to tuple (because I read an article that this helps
to block less writing back to memory) and store data in
UnsafedMutablePointer to reduce overhead of array access.
modified by Patrick Sy
*/
import Foundation
typealias Body = (
r: (x: Double, y: Double, z: Double),
v: (x: Double, y: Double, z: Double),
m: Double, d: Double
)
let nPlanets: Int = 5
let solarMass: Double = 4 * Double.pi * Double.pi
let daysPerYear: Double = 365.24
let sun: Body = (
r: (x: 0.0, y: 0.0, z: 0.0),
v: (x: 0.0, y: 0.0, z: 0.0),
m: solarMass, d: 0.0
)
let jupiter: Body = (
r: (x: 4.8414314424647209,
y: -1.16032004402742839,
z: -0.103622044471123109),
v: (x: 1.66007664274403694e-03 * daysPerYear,
y: 7.69901118419740425e-03 * daysPerYear,
z: -6.90460016972063023e-05 * daysPerYear),
m: 9.54791938424326609e-04 * solarMass, d: 0.0
)
let saturn: Body = (
r: (x: 8.34336671824457987,
y: 4.12479856412430479,
z: -4.03523417114321381e-01),
v: (x: -2.76742510726862411e-03 * daysPerYear,
y: 4.99852801234917238e-03 * daysPerYear,
z: 2.30417297573763929e-05 * daysPerYear),
m: 2.85885980666130812e-04 * solarMass, d: 0.0
)
let uranus: Body = (
r: (x: 1.28943695621391310e+01,
y: -1.51111514016986312e+01,
z: -2.23307578892655734e-01),
v: (x: 2.96460137564761618e-03 * daysPerYear,
y: 2.37847173959480950e-03 * daysPerYear,
z: -2.96589568540237556e-05 * daysPerYear),
m: 4.36624404335156298e-05 * solarMass, d: 0.0
)
let neptune: Body = (
r: (x: 1.53796971148509165e+01,
y: -2.59193146099879641e+01,
z: 1.79258772950371181e-01),
v: (x: 2.68067772490389322e-03 * daysPerYear,
y: 1.62824170038242295e-03 * daysPerYear,
z: -9.51592254519715870e-05 * daysPerYear),
m: 5.15138902046611451e-05 * solarMass, d: 0.0
)
let bodies: UnsafeMutablePointer<Body> = UnsafeMutablePointer<Body>.allocate(capacity: nPlanets)
defer {
bodies.deallocate()
}
bodies[0] = sun
bodies[1] = jupiter
bodies[2] = saturn
bodies[3] = uranus
bodies[4] = neptune
func advance(_ bodies: UnsafeMutablePointer<Body>, n: Int, dt: Double) {
for i in 0..<n {
let iBody: Body = bodies[i]
for j in i+1..<n {
let jBody: Body = bodies[j]
let dx: Double = iBody.r.x - jBody.r.x
let dy: Double = iBody.r.y - jBody.r.y
let dz: Double = iBody.r.z - jBody.r.z
let dSquared: Double = dx*dx + dy*dy + dz*dz
let mag: Double = dt / (dSquared * dSquared.squareRoot())
// dSquared.squareRoot() == distance
bodies[i].v = (bodies[i].v.x - dx * jBody.m * mag,
bodies[i].v.y - dy * jBody.m * mag,
bodies[i].v.z - dz * jBody.m * mag)
bodies[j].v = (bodies[j].v.x + dx * iBody.m * mag,
bodies[j].v.y + dy * iBody.m * mag,
bodies[j].v.z + dz * iBody.m * mag)
}
}
for i in 0..<n {
bodies[i].r = (
bodies[i].r.x + dt * bodies[i].v.x,
bodies[i].r.y + dt * bodies[i].v.y,
bodies[i].r.z + dt * bodies[i].v.z
)
}
}
func energy(_ bodies: UnsafeMutablePointer<Body>, n: Int) -> Double {
var energy: Double = 0.0
for i in 0..<n {
let iBody: Body = bodies[i]
energy += 0.5 * iBody.m * ( iBody.v.x * iBody.v.x +
iBody.v.y * iBody.v.y +
iBody.v.z * iBody.v.z)
for j in i+1..<n {
let jBody: Body = bodies[j]
let dx: Double = iBody.r.x - jBody.r.x
let dy: Double = iBody.r.y - jBody.r.y
let dz: Double = iBody.r.z - jBody.r.z
let distance: Double = (dx*dx + dy*dy + dz*dz).squareRoot()
energy -= (iBody.m * jBody.m) / distance
}
}
return energy
}
var n: Int = 1000
if CommandLine.argc > 1 {
if let m: Int = Int(CommandLine.arguments[1]) {
n = m
}
}
// Adjust momentum of the sun
var p: (Double, Double, Double) = (0.0, 0.0, 0.0)
for i in 0..<nPlanets {
p.0 += bodies[i].v.x * bodies[i].m
p.1 += bodies[i].v.y * bodies[i].m
p.2 += bodies[i].v.z * bodies[i].m
}
bodies[0].1 = (-p.0 / solarMass, -p.1 / solarMass, -p.2 / solarMass)
print(String(format: "%.9f", energy(bodies, n: nPlanets)))
for _ in 0..<n {
advance(bodies, n: nPlanets, dt: 0.01)
}
print(String(format: "%.9f", energy(bodies, n: nPlanets)))