blob: d68e8f01f21d1b43737a3a6d9fe2cc265d146d3f [file] [log] [blame]
 /* The Computer Language Benchmarks Game * http://benchmarksgame.alioth.debian.org/ * * contributed by Christoph Bauer * slightly sped up by Petr Prokhorenkov */ #include #include #include #define pi 3.141592653589793 #define solar_mass (4 * pi * pi) #define days_per_year 365.24 struct planet { double x, y, z; double vx, vy, vz; double mass; }; /* * Here's one weird thing: inlining of this function * decreases performance by 25%. (I.e. do not compile this with -O3) * Advances with dt == 1.0 */ void advance(int nbodies, struct planet * bodies) { int i, j; for (i = 0; i < nbodies; i++) { struct planet * b = &(bodies[i]); for (j = i + 1; j < nbodies; j++) { struct planet * b2 = &(bodies[j]); double dx = b->x - b2->x; double dy = b->y - b2->y; double dz = b->z - b2->z; double inv_distance = 1.0/sqrt(dx * dx + dy * dy + dz * dz); double mag = inv_distance * inv_distance * inv_distance; b->vx -= dx * b2->mass * mag; b->vy -= dy * b2->mass * mag; b->vz -= dz * b2->mass * mag; b2->vx += dx * b->mass * mag; b2->vy += dy * b->mass * mag; b2->vz += dz * b->mass * mag; } } for (i = 0; i < nbodies; i++) { struct planet * b = &(bodies[i]); b->x += b->vx; b->y += b->vy; b->z += b->vz; } } double energy(int nbodies, struct planet * bodies) { double e; int i, j; e = 0.0; for (i = 0; i < nbodies; i++) { struct planet * b = &(bodies[i]); e += 0.5 * b->mass * (b->vx * b->vx + b->vy * b->vy + b->vz * b->vz); for (j = i + 1; j < nbodies; j++) { struct planet * b2 = &(bodies[j]); double dx = b->x - b2->x; double dy = b->y - b2->y; double dz = b->z - b2->z; double distance = sqrt(dx * dx + dy * dy + dz * dz); e -= (b->mass * b2->mass) / distance; } } return e; } void offset_momentum(int nbodies, struct planet * bodies) { double px = 0.0, py = 0.0, pz = 0.0; int i; for (i = 0; i < nbodies; i++) { px += bodies[i].vx * bodies[i].mass; py += bodies[i].vy * bodies[i].mass; pz += bodies[i].vz * bodies[i].mass; } bodies[0].vx = - px / solar_mass; bodies[0].vy = - py / solar_mass; bodies[0].vz = - pz / solar_mass; } #define NBODIES 5 struct planet bodies[NBODIES] = { { /* sun */ 0, 0, 0, 0, 0, 0, solar_mass }, { /* jupiter */ 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 }, { /* saturn */ 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 }, { /* uranus */ 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 }, { /* neptune */ 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 } }; #define DT 1e-2 #define RECIP_DT (1.0/DT) /* * Rescale certain properties of bodies. That allows doing * consequential advance()'s as if dt were equal to 1.0. * * When all advances done, rescale bodies back to obtain correct energy. */ void scale_bodies(int nbodies, struct planet * bodies, double scale) { int i; for (i = 0; i < nbodies; i++) { bodies[i].mass *= scale*scale; bodies[i].vx *= scale; bodies[i].vy *= scale; bodies[i].vz *= scale; } } int main(int argc, char ** argv) { int n = atoi(argv[1]); int i; offset_momentum(NBODIES, bodies); printf ("%.9f\n", energy(NBODIES, bodies)); scale_bodies(NBODIES, bodies, DT); for (i = 1; i <= n; i++) { advance(NBODIES, bodies); } scale_bodies(NBODIES, bodies, RECIP_DT); printf ("%.9f\n", energy(NBODIES, bodies)); return 0; }