# n-body C clang #3 program

## source code

```/* The Computer Language Benchmarks Game
* https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
*
* contributed by Ledrug Katz
*
*   compile: gcc -Wall -O3 -fomit-frame-pointer -lm -mfpmath=sse
*/

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

#define pi 3.141592653589793
#define solar_mass (4 * pi * pi)
#define year 365.24
#define for_k for(k = 0; k < 3; k++)

typedef struct planet { double x[3], v[3], mass; } planet;

void advance(int nbodies, struct planet *bodies, double dt, int steps)
{
int i, j;
register planet *a, *b;
double d[3], d2, mag;

while (steps--) {
for (a = bodies, i = 0; i < nbodies; a++, i++) {
for (b = a + 1, j = i + 1; j < nbodies; b++, j++) {
d[0] = a->x[0] - b->x[0];
d[1] = a->x[1] - b->x[1];
d[2] = a->x[2] - b->x[2];

d2 = d[0] * d[0] + d[1] * d[1] + d[2] * d[2];
mag = dt / (d2 * sqrt(d2));

a->v[0] -= d[0] * b->mass * mag;
a->v[1] -= d[1] * b->mass * mag;
a->v[2] -= d[2] * b->mass * mag;

b->v[0] += d[0] * a->mass * mag;
b->v[1] += d[1] * a->mass * mag;
b->v[2] += d[2] * a->mass * mag;
}
}

for (a = bodies, i = 0; i < nbodies; i++, a++) {
a->x[0] += dt * a->v[0];
a->x[1] += dt * a->v[1];
a->x[2] += dt * a->v[2];
}
}
}

double energy(int nbodies, planet *bodies)
{
double e, d[3];
int i, j, k;
planet *a, *b;

e = 0.0;
for (i = 0, a = bodies; i < nbodies; a++, i++) {
for_k { e += a->mass * a->v[k] * a->v[k] / 2; }

for (j = i + 1, b = a + 1; j < nbodies; b++, j++) {
for_k { d[k] = a->x[k] - b->x[k]; }
e -= (a->mass * b->mass) /
sqrt(d[0] * d[0] + d[1] * d[1] + d[2] * d[2]);
}
}
return e;
}

void offset_momentum(int nbodies, planet *bodies)
{
int i, k;
for (i = 0; i < nbodies; i++)
for_k { bodies[0].v[k] -= bodies[i].v[k] * bodies[i].mass / solar_mass; }
}

struct planet bodies[] = {
{   /* sun */
{0, 0, 0},
{0, 0, 0},
solar_mass
}, {   /* jupiter */
{ 4.84143144246472090e+00, -1.16032004402742839e+00, -1.03622044471123109e-01 },
{
1.66007664274403694e-03 * year,
7.69901118419740425e-03 * year,
-6.90460016972063023e-05 * year
},
9.54791938424326609e-04 * solar_mass
}, {   /* saturn */
{ 8.34336671824457987e+00, 4.12479856412430479e+00, -4.03523417114321381e-01 },
{
-2.76742510726862411e-03 * year,
4.99852801234917238e-03 * year,
2.30417297573763929e-05 * year
},
2.85885980666130812e-04 * solar_mass
}, {   /* uranus */
{ 1.28943695621391310e+01, -1.51111514016986312e+01, -2.23307578892655734e-01 },
{
2.96460137564761618e-03 * year,
2.37847173959480950e-03 * year,
-2.96589568540237556e-05 * year
},
4.36624404335156298e-05 * solar_mass
}, {   /* neptune */
{ 1.53796971148509165e+01, -2.59193146099879641e+01, 1.79258772950371181e-01 },
{
2.68067772490389322e-03 * year,
1.62824170038242295e-03 * year,
-9.51592254519715870e-05 * year
},
5.15138902046611451e-05 * solar_mass
}
};

#define N sizeof(bodies)/sizeof(planet)

int main(int argc, char **argv)
{
int n = atoi(argv[1]);

offset_momentum(N, bodies);
printf("%.9f\n", energy(N, bodies));

advance(N, bodies, 0.01, n);

printf("%.9f\n", energy(N, bodies));
return 0;
}
```

## notes, command-line, and program output

```NOTES:
64-bit Ubuntu quad core
Ubuntu clang version 18.1.3

Thu, 06 Jun 2024 22:12:25 GMT

MAKE:
/usr/bin/clang -pipe -Wall -O3 -fomit-frame-pointer -march=ivybridge  nbody.clang-3.c -o nbody.clang-3.clang_run -lm
rm nbody.clang-3.c

6.28s to complete and log all make actions

COMMAND LINE:
./nbody.clang-3.clang_run 50000000

PROGRAM OUTPUT:
-0.169075164
-0.169059907
```