Hastebin

// N-body benchmark - C reference nbody.c from github.com/korulang/koru/...
// Compiled with: gcc -O3 -ffast-math -march=native -o nbody nbody.c -lm
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
//#include <omp.h>

#define PI 3.141592653589793
#define SOLAR_MASS (4 * PI * PI)
#define DAYS_PER_YEAR 365.24
#define NBODIES 5

struct body {
    double x, y, z;
    double vx, vy, vz;
    double mass;
};

// Global array for better optimization
struct body bodies[NBODIES]={0};
struct body bodies_ref[NBODIES] = {
    { 0, 0, 0, 0, 0, 0, SOLAR_MASS },
    { 4.84143144246472090e+00, -1.16032004402742839e+00, -1.03622044471123109e-01, 1.66007664274403694e-03 * DAYS_PER_YEAR, 7.69901118419740425e-03 * DAYS_PER_YEAR, -6.90460016972063023e-05 * DAYS_PER_YEAR, 9.54791938424326609e-04 * SOLAR_MASS },
    { 8.34336671824457987e+00, 4.12479856412430479e+00, -4.03523417114321381e-01, -2.76742510726862411e-03 * DAYS_PER_YEAR, 4.99852801234917238e-03 * DAYS_PER_YEAR, 2.30417297573763929e-05 * DAYS_PER_YEAR, 2.85885980666130812e-04 * SOLAR_MASS },
    { 1.28943695621391310e+01, -1.51111514016986312e+01, -2.23307578892655734e-01, 2.96460137564761618e-03 * DAYS_PER_YEAR, 2.37847173959480950e-03 * DAYS_PER_YEAR, -2.96589568540237556e-05 * DAYS_PER_YEAR, 4.36624404335156298e-05 * SOLAR_MASS },
    { 1.53796971148509165e+01, -2.59193146099879641e+01, 1.79258772950371181e-01, 2.68067772490389322e-03 * DAYS_PER_YEAR, 1.62824170038242295e-03 * DAYS_PER_YEAR, -9.51592254519715870e-05 * DAYS_PER_YEAR, 5.15138902046611451e-05 * SOLAR_MASS },
};


static void
reset_bodies(){
    memcpy(bodies, bodies_ref, sizeof(bodies_ref));
}


static inline void advance(struct body * restrict b, double dt) {
    for (int i = 0; i < 5; i++) {
        for (int j = i + 1; j < 5; j++) {
            double dx = b[i].x - b[j].x;
            double dy = b[i].y - b[j].y;
            double dz = b[i].z - b[j].z;
            double dsq = dx * dx + dy * dy + dz * dz;
            double mag = dt / (dsq * sqrt(dsq) );

            b[i].vx -= dx * b[j].mass * mag;
            b[i].vy -= dy * b[j].mass * mag;
            b[i].vz -= dz * b[j].mass * mag;
            b[j].vx += dx * b[i].mass * mag;
            b[j].vy += dy * b[i].mass * mag;
            b[j].vz += dz * b[i].mass * mag;
        }
    }
    for (int i = 0; i < 5; i++) {
        b[i].x += dt * b[i].vx;
        b[i].y += dt * b[i].vy;
        b[i].z += dt * b[i].vz;
    }
}

static double energy(struct body *b) {
    double e = 0.0;
    for (int i = 0; i < NBODIES; i++) {
        e += 0.5 * b[i].mass * (b[i].vx * b[i].vx + b[i].vy * b[i].vy + b[i].vz * b[i].vz);
        for (int j = i + 1; j < NBODIES; j++) {
            double dx = b[i].x - b[j].x;
            double dy = b[i].y - b[j].y;
            double dz = b[i].z - b[j].z;
            e -= (b[i].mass * b[j].mass) / sqrt(dx * dx + dy * dy + dz * dz);
        }
    }
    return e;
}

double
take_energy(long n){
    reset_bodies();
    for(long i = 0; i < n; ++i){
        advance(bodies, 0.01);
    }
    return energy(bodies);
}