1 /* The Computer Language Benchmarks Game
2 * http://benchmarksgame.alioth.debian.org/
4 * contributed by Christoph Bauer
5 * slightly sped up by Petr Prokhorenkov
12 #define pi 3.141592653589793
13 #define solar_mass (4 * pi * pi)
14 #define days_per_year 365.24
23 * Here's one weird thing: inlining of this function
24 * decreases performance by 25%. (I.e. do not compile this with -O3)
25 * Advances with dt == 1.0
27 void advance(int nbodies, struct planet * bodies)
31 for (i = 0; i < nbodies; i++) {
32 struct planet * b = &(bodies[i]);
33 for (j = i + 1; j < nbodies; j++) {
34 struct planet * b2 = &(bodies[j]);
35 double dx = b->x - b2->x;
36 double dy = b->y - b2->y;
37 double dz = b->z - b2->z;
38 double inv_distance = 1.0/sqrt(dx * dx + dy * dy + dz * dz);
39 double mag = inv_distance * inv_distance * inv_distance;
40 b->vx -= dx * b2->mass * mag;
41 b->vy -= dy * b2->mass * mag;
42 b->vz -= dz * b2->mass * mag;
43 b2->vx += dx * b->mass * mag;
44 b2->vy += dy * b->mass * mag;
45 b2->vz += dz * b->mass * mag;
48 for (i = 0; i < nbodies; i++) {
49 struct planet * b = &(bodies[i]);
56 double energy(int nbodies, struct planet * bodies)
62 for (i = 0; i < nbodies; i++) {
63 struct planet * b = &(bodies[i]);
64 e += 0.5 * b->mass * (b->vx * b->vx + b->vy * b->vy + b->vz * b->vz);
65 for (j = i + 1; j < nbodies; j++) {
66 struct planet * b2 = &(bodies[j]);
67 double dx = b->x - b2->x;
68 double dy = b->y - b2->y;
69 double dz = b->z - b2->z;
70 double distance = sqrt(dx * dx + dy * dy + dz * dz);
71 e -= (b->mass * b2->mass) / distance;
77 void offset_momentum(int nbodies, struct planet * bodies)
79 double px = 0.0, py = 0.0, pz = 0.0;
81 for (i = 0; i < nbodies; i++) {
82 px += bodies[i].vx * bodies[i].mass;
83 py += bodies[i].vy * bodies[i].mass;
84 pz += bodies[i].vz * bodies[i].mass;
86 bodies[0].vx = - px / solar_mass;
87 bodies[0].vy = - py / solar_mass;
88 bodies[0].vz = - pz / solar_mass;
92 struct planet bodies[NBODIES] = {
94 0, 0, 0, 0, 0, 0, solar_mass
97 4.84143144246472090e+00,
98 -1.16032004402742839e+00,
99 -1.03622044471123109e-01,
100 1.66007664274403694e-03 * days_per_year,
101 7.69901118419740425e-03 * days_per_year,
102 -6.90460016972063023e-05 * days_per_year,
103 9.54791938424326609e-04 * solar_mass
106 8.34336671824457987e+00,
107 4.12479856412430479e+00,
108 -4.03523417114321381e-01,
109 -2.76742510726862411e-03 * days_per_year,
110 4.99852801234917238e-03 * days_per_year,
111 2.30417297573763929e-05 * days_per_year,
112 2.85885980666130812e-04 * solar_mass
115 1.28943695621391310e+01,
116 -1.51111514016986312e+01,
117 -2.23307578892655734e-01,
118 2.96460137564761618e-03 * days_per_year,
119 2.37847173959480950e-03 * days_per_year,
120 -2.96589568540237556e-05 * days_per_year,
121 4.36624404335156298e-05 * solar_mass
124 1.53796971148509165e+01,
125 -2.59193146099879641e+01,
126 1.79258772950371181e-01,
127 2.68067772490389322e-03 * days_per_year,
128 1.62824170038242295e-03 * days_per_year,
129 -9.51592254519715870e-05 * days_per_year,
130 5.15138902046611451e-05 * solar_mass
135 #define RECIP_DT (1.0/DT)
138 * Rescale certain properties of bodies. That allows doing
139 * consequential advance()'s as if dt were equal to 1.0.
141 * When all advances done, rescale bodies back to obtain correct energy.
143 void scale_bodies(int nbodies, struct planet * bodies, double scale) {
146 for (i = 0; i < nbodies; i++) {
147 bodies[i].mass *= scale*scale;
148 bodies[i].vx *= scale;
149 bodies[i].vy *= scale;
150 bodies[i].vz *= scale;
154 int main(int argc, char ** argv)
156 int n = atoi(argv[1]);
159 offset_momentum(NBODIES, bodies);
160 printf ("%.9f\n", energy(NBODIES, bodies));
161 scale_bodies(NBODIES, bodies, DT);
162 for (i = 1; i <= n; i++) {
163 advance(NBODIES, bodies);
165 scale_bodies(NBODIES, bodies, RECIP_DT);
166 printf ("%.9f\n", energy(NBODIES, bodies));