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Diffstat (limited to 'library/portable-simd/crates/core_simd/examples/nbody.rs')
| -rw-r--r-- | library/portable-simd/crates/core_simd/examples/nbody.rs | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/library/portable-simd/crates/core_simd/examples/nbody.rs b/library/portable-simd/crates/core_simd/examples/nbody.rs new file mode 100644 index 000000000..df38a0096 --- /dev/null +++ b/library/portable-simd/crates/core_simd/examples/nbody.rs @@ -0,0 +1,193 @@ +#![feature(portable_simd)] +extern crate std_float; + +/// Benchmarks game nbody code +/// Taken from the `packed_simd` crate +/// Run this benchmark with `cargo test --example nbody` +mod nbody { + use core_simd::simd::*; + #[allow(unused)] // False positive? + use std_float::StdFloat; + + use std::f64::consts::PI; + const SOLAR_MASS: f64 = 4.0 * PI * PI; + const DAYS_PER_YEAR: f64 = 365.24; + + #[derive(Debug, Clone, Copy)] + struct Body { + pub x: f64x4, + pub v: f64x4, + pub mass: f64, + } + + const N_BODIES: usize = 5; + const BODIES: [Body; N_BODIES] = [ + // sun: + Body { + x: f64x4::from_array([0., 0., 0., 0.]), + v: f64x4::from_array([0., 0., 0., 0.]), + mass: SOLAR_MASS, + }, + // jupiter: + Body { + x: f64x4::from_array([ + 4.84143144246472090e+00, + -1.16032004402742839e+00, + -1.03622044471123109e-01, + 0., + ]), + v: f64x4::from_array([ + 1.66007664274403694e-03 * DAYS_PER_YEAR, + 7.69901118419740425e-03 * DAYS_PER_YEAR, + -6.90460016972063023e-05 * DAYS_PER_YEAR, + 0., + ]), + mass: 9.54791938424326609e-04 * SOLAR_MASS, + }, + // saturn: + Body { + x: f64x4::from_array([ + 8.34336671824457987e+00, + 4.12479856412430479e+00, + -4.03523417114321381e-01, + 0., + ]), + v: f64x4::from_array([ + -2.76742510726862411e-03 * DAYS_PER_YEAR, + 4.99852801234917238e-03 * DAYS_PER_YEAR, + 2.30417297573763929e-05 * DAYS_PER_YEAR, + 0., + ]), + mass: 2.85885980666130812e-04 * SOLAR_MASS, + }, + // uranus: + Body { + x: f64x4::from_array([ + 1.28943695621391310e+01, + -1.51111514016986312e+01, + -2.23307578892655734e-01, + 0., + ]), + v: f64x4::from_array([ + 2.96460137564761618e-03 * DAYS_PER_YEAR, + 2.37847173959480950e-03 * DAYS_PER_YEAR, + -2.96589568540237556e-05 * DAYS_PER_YEAR, + 0., + ]), + mass: 4.36624404335156298e-05 * SOLAR_MASS, + }, + // neptune: + Body { + x: f64x4::from_array([ + 1.53796971148509165e+01, + -2.59193146099879641e+01, + 1.79258772950371181e-01, + 0., + ]), + v: f64x4::from_array([ + 2.68067772490389322e-03 * DAYS_PER_YEAR, + 1.62824170038242295e-03 * DAYS_PER_YEAR, + -9.51592254519715870e-05 * DAYS_PER_YEAR, + 0., + ]), + mass: 5.15138902046611451e-05 * SOLAR_MASS, + }, + ]; + + fn offset_momentum(bodies: &mut [Body; N_BODIES]) { + let (sun, rest) = bodies.split_at_mut(1); + let sun = &mut sun[0]; + for body in rest { + let m_ratio = body.mass / SOLAR_MASS; + sun.v -= body.v * Simd::splat(m_ratio); + } + } + + fn energy(bodies: &[Body; N_BODIES]) -> f64 { + let mut e = 0.; + for i in 0..N_BODIES { + let bi = &bodies[i]; + e += bi.mass * (bi.v * bi.v).reduce_sum() * 0.5; + for bj in bodies.iter().take(N_BODIES).skip(i + 1) { + let dx = bi.x - bj.x; + e -= bi.mass * bj.mass / (dx * dx).reduce_sum().sqrt() + } + } + e + } + + fn advance(bodies: &mut [Body; N_BODIES], dt: f64) { + const N: usize = N_BODIES * (N_BODIES - 1) / 2; + + // compute distance between bodies: + let mut r = [f64x4::splat(0.); N]; + { + let mut i = 0; + for j in 0..N_BODIES { + for k in j + 1..N_BODIES { + r[i] = bodies[j].x - bodies[k].x; + i += 1; + } + } + } + + let mut mag = [0.0; N]; + for i in (0..N).step_by(2) { + let d2s = f64x2::from_array([ + (r[i] * r[i]).reduce_sum(), + (r[i + 1] * r[i + 1]).reduce_sum(), + ]); + let dmags = f64x2::splat(dt) / (d2s * d2s.sqrt()); + mag[i] = dmags[0]; + mag[i + 1] = dmags[1]; + } + + let mut i = 0; + for j in 0..N_BODIES { + for k in j + 1..N_BODIES { + let f = r[i] * Simd::splat(mag[i]); + bodies[j].v -= f * Simd::splat(bodies[k].mass); + bodies[k].v += f * Simd::splat(bodies[j].mass); + i += 1 + } + } + for body in bodies { + body.x += Simd::splat(dt) * body.v + } + } + + pub fn run(n: usize) -> (f64, f64) { + let mut bodies = BODIES; + offset_momentum(&mut bodies); + let energy_before = energy(&bodies); + for _ in 0..n { + advance(&mut bodies, 0.01); + } + let energy_after = energy(&bodies); + + (energy_before, energy_after) + } +} + +#[cfg(test)] +mod tests { + // Good enough for demonstration purposes, not going for strictness here. + fn approx_eq_f64(a: f64, b: f64) -> bool { + (a - b).abs() < 0.00001 + } + #[test] + fn test() { + const OUTPUT: [f64; 2] = [-0.169075164, -0.169087605]; + let (energy_before, energy_after) = super::nbody::run(1000); + assert!(approx_eq_f64(energy_before, OUTPUT[0])); + assert!(approx_eq_f64(energy_after, OUTPUT[1])); + } +} + +fn main() { + { + let (energy_before, energy_after) = nbody::run(1000); + println!("Energy before: {energy_before}"); + println!("Energy after: {energy_after}"); + } +} |