1 /// Benchmarks game nbody code
2 /// Taken from the `packed_simd` crate
3 /// Run this benchmark with `cargo test --example body`
6 use std::f64::consts::PI;
7 const SOLAR_MASS: f64 = 4.0 * PI * PI;
8 const DAYS_PER_YEAR: f64 = 365.24;
10 #[derive(Debug, Clone, Copy)]
17 // translation up to here
18 const N_BODIES: usize = 5;
19 const BODIES: [Body; N_BODIES] = [
22 x: f64x4::from_array([0., 0., 0., 0.]),
23 v: f64x4::from_array([0., 0., 0., 0.]),
28 x: f64x4::from_array([
29 4.84143144246472090e+00,
30 -1.16032004402742839e+00,
31 -1.03622044471123109e-01,
34 v: f64x4::from_array([
35 1.66007664274403694e-03 * DAYS_PER_YEAR,
36 7.69901118419740425e-03 * DAYS_PER_YEAR,
37 -6.90460016972063023e-05 * DAYS_PER_YEAR,
40 mass: 9.54791938424326609e-04 * SOLAR_MASS,
44 x: f64x4::from_array([
45 8.34336671824457987e+00,
46 4.12479856412430479e+00,
47 -4.03523417114321381e-01,
50 v: f64x4::from_array([
51 -2.76742510726862411e-03 * DAYS_PER_YEAR,
52 4.99852801234917238e-03 * DAYS_PER_YEAR,
53 2.30417297573763929e-05 * DAYS_PER_YEAR,
56 mass: 2.85885980666130812e-04 * SOLAR_MASS,
60 x: f64x4::from_array([
61 1.28943695621391310e+01,
62 -1.51111514016986312e+01,
63 -2.23307578892655734e-01,
66 v: f64x4::from_array([
67 2.96460137564761618e-03 * DAYS_PER_YEAR,
68 2.37847173959480950e-03 * DAYS_PER_YEAR,
69 -2.96589568540237556e-05 * DAYS_PER_YEAR,
72 mass: 4.36624404335156298e-05 * SOLAR_MASS,
76 x: f64x4::from_array([
77 1.53796971148509165e+01,
78 -2.59193146099879641e+01,
79 1.79258772950371181e-01,
82 v: f64x4::from_array([
83 2.68067772490389322e-03 * DAYS_PER_YEAR,
84 1.62824170038242295e-03 * DAYS_PER_YEAR,
85 -9.51592254519715870e-05 * DAYS_PER_YEAR,
88 mass: 5.15138902046611451e-05 * SOLAR_MASS,
92 pub fn offset_momentum(bodies: &mut [Body; N_BODIES]) {
93 let (sun, rest) = bodies.split_at_mut(1);
94 let sun = &mut sun[0];
96 let m_ratio = body.mass / SOLAR_MASS;
97 sun.v -= body.v * m_ratio;
101 pub fn energy(bodies: &[Body; N_BODIES]) -> f64 {
103 for i in 0..N_BODIES {
105 e += bi.mass * (bi.v * bi.v).horizontal_sum() * 0.5;
106 for bj in bodies.iter().take(N_BODIES).skip(i + 1) {
107 let dx = bi.x - bj.x;
108 e -= bi.mass * bj.mass / (dx * dx).horizontal_sum().sqrt()
114 pub fn advance(bodies: &mut [Body; N_BODIES], dt: f64) {
115 const N: usize = N_BODIES * (N_BODIES - 1) / 2;
117 // compute distance between bodies:
118 let mut r = [f64x4::splat(0.); N];
121 for j in 0..N_BODIES {
122 for k in j + 1..N_BODIES {
123 r[i] = bodies[j].x - bodies[k].x;
129 let mut mag = [0.0; N];
132 let d2s = f64x2::from_array([
133 (r[i] * r[i]).horizontal_sum(),
134 (r[i + 1] * r[i + 1]).horizontal_sum(),
136 let dmags = f64x2::splat(dt) / (d2s * d2s.sqrt());
137 // dmags.write_to_slice_unaligned(&mut mag[i..]);
139 mag[i + 1] = dmags[1];
144 for j in 0..N_BODIES {
145 for k in j + 1..N_BODIES {
146 let f = r[i] * mag[i];
147 bodies[j].v -= f * bodies[k].mass;
148 bodies[k].v += f * bodies[j].mass;
153 body.x += dt * body.v
158 // pub unsafe fn write_to_slice_unaligned(slice: &mut SimdF64::<LANES>) {
159 // let target_ptr = slice.get_unchecked_mut(0) as *mut f64x2;
160 // *(target_ptr as *mut f64x2) = SimdF64;
163 pub fn run(n: usize) -> (f64, f64) {
164 let mut bodies = BODIES;
165 offset_momentum(&mut bodies);
166 let energy_before = energy(&bodies);
168 advance(&mut bodies, 0.01);
170 let energy_after = energy(&bodies);
172 (energy_before, energy_after)
175 fn approx_eq_f32(a: f32, b: f32) -> bool {
176 (a - b).abs() < 0.00000001
184 const OUTPUT: [f64; 2] = [-0.169075164, -0.169087605];
185 let (energy_before, energy_after) = super::run(1000);
186 assert!(approx_eq_f32(energy_before as f32, OUTPUT[0] as f32));
187 assert!(approx_eq_f32(energy_after as f32, OUTPUT[1] as f32));
193 // empty main to pass CI