modernc.org/ccgo/v3@v3.16.14/lib/testdata/CompCert-3.6/test/c/nbody.c (about)

     1  /*
     2   * The Great Computer Language Shootout
     3   * http://shootout.alioth.debian.org/
     4   *
     5   * contributed by Christoph Bauer
     6   *
     7   */
     8  
     9  #include <math.h>
    10  #include <stdio.h>
    11  #include <stdlib.h>
    12  
    13  #define pi 3.141592653589793
    14  #define solar_mass (4 * pi * pi)
    15  #define days_per_year 365.24
    16  
    17  struct planet {
    18    double x, y, z;
    19    double vx, vy, vz;
    20    double mass;
    21  };
    22  
    23  void advance(int nbodies, struct planet * bodies, double dt)
    24  {
    25    int i, j;
    26  
    27    for (i = 0; i < nbodies; i++) {
    28      struct planet * b = &(bodies[i]);
    29      for (j = i + 1; j < nbodies; j++) {
    30        struct planet * b2 = &(bodies[j]);
    31        double dx = b->x - b2->x;
    32        double dy = b->y - b2->y;
    33        double dz = b->z - b2->z;
    34        double distance = sqrt(dx * dx + dy * dy + dz * dz);
    35        double mag = dt / (distance * distance * distance);
    36        b->vx -= dx * b2->mass * mag;
    37        b->vy -= dy * b2->mass * mag;
    38        b->vz -= dz * b2->mass * mag;
    39        b2->vx += dx * b->mass * mag;
    40        b2->vy += dy * b->mass * mag;
    41        b2->vz += dz * b->mass * mag;
    42      }
    43    }
    44    for (i = 0; i < nbodies; i++) {
    45      struct planet * b = &(bodies[i]);
    46      b->x += dt * b->vx;
    47      b->y += dt * b->vy;
    48      b->z += dt * b->vz;
    49    }
    50  }
    51  
    52  double energy(int nbodies, struct planet * bodies)
    53  {
    54    double e;
    55    int i, j;
    56  
    57    e = 0.0;
    58    for (i = 0; i < nbodies; i++) {
    59      struct planet * b = &(bodies[i]);
    60      e += 0.5 * b->mass * (b->vx * b->vx + b->vy * b->vy + b->vz * b->vz);
    61      for (j = i + 1; j < nbodies; j++) {
    62        struct planet * b2 = &(bodies[j]);
    63        double dx = b->x - b2->x;
    64        double dy = b->y - b2->y;
    65        double dz = b->z - b2->z;
    66        double distance = sqrt(dx * dx + dy * dy + dz * dz);
    67        e -= (b->mass * b2->mass) / distance;
    68      }
    69    }
    70    return e;
    71  }
    72  
    73  void offset_momentum(int nbodies, struct planet * bodies)
    74  {
    75    double px = 0.0, py = 0.0, pz = 0.0;
    76    int i;
    77    for (i = 0; i < nbodies; i++) {
    78      px += bodies[i].vx * bodies[i].mass;
    79      py += bodies[i].vy * bodies[i].mass;
    80      pz += bodies[i].vz * bodies[i].mass;
    81    }
    82    bodies[0].vx = - px / solar_mass;
    83    bodies[0].vy = - py / solar_mass;
    84    bodies[0].vz = - pz / solar_mass;
    85  }
    86  
    87  #define NBODIES 5
    88  struct planet bodies[NBODIES] = {
    89    {                               /* sun */
    90      0, 0, 0, 0, 0, 0, 1.0 /*solar_mass*/
    91    },
    92    {                               /* jupiter */
    93      4.84143144246472090e+00,
    94      -1.16032004402742839e+00,
    95      -1.03622044471123109e-01,
    96      1.66007664274403694e-03 /* * days_per_year */,
    97      7.69901118419740425e-03 /* * days_per_year */,
    98      -6.90460016972063023e-05 /* * days_per_year */,
    99      9.54791938424326609e-04 /* * solar_mass */
   100    },
   101    {                               /* saturn */
   102      8.34336671824457987e+00,
   103      4.12479856412430479e+00,
   104      -4.03523417114321381e-01,
   105      -2.76742510726862411e-03 /* * days_per_year */,
   106      4.99852801234917238e-03 /* * days_per_year */,
   107      2.30417297573763929e-05 /* * days_per_year */,
   108      2.85885980666130812e-04 /* * solar_mass */
   109    },
   110    {                               /* uranus */
   111      1.28943695621391310e+01,
   112      -1.51111514016986312e+01,
   113      -2.23307578892655734e-01,
   114      2.96460137564761618e-03 /* * days_per_year */,
   115      2.37847173959480950e-03 /* * days_per_year */,
   116      -2.96589568540237556e-05 /* * days_per_year */,
   117      4.36624404335156298e-05 /* * solar_mass */
   118    },
   119    {                               /* neptune */
   120      1.53796971148509165e+01,
   121      -2.59193146099879641e+01,
   122      1.79258772950371181e-01,
   123      2.68067772490389322e-03 /* * days_per_year */,
   124      1.62824170038242295e-03 /* * days_per_year */,
   125      -9.51592254519715870e-05 /* * days_per_year */,
   126      5.15138902046611451e-05 /* * solar_mass */
   127    }
   128  };
   129  
   130  void setup_bodies(void)
   131  {
   132    int i;
   133    for (i = 0; i < NBODIES; i++) {
   134      bodies[i].vx *= days_per_year;
   135      bodies[i].vy *= days_per_year;
   136      bodies[i].vz *= days_per_year;
   137      bodies[i].mass *= solar_mass;
   138    }
   139  }
   140  
   141  int main(int argc, char ** argv)
   142  {
   143    int n = argc < 2 ? 1000000 : atoi(argv[1]);
   144    int i;
   145  
   146    setup_bodies();
   147    offset_momentum(NBODIES, bodies);
   148    printf ("%.9f\n", energy(NBODIES, bodies));
   149    for (i = 1; i <= n; i++)
   150      advance(NBODIES, bodies, 0.01);
   151    printf ("%.9f\n", energy(NBODIES, bodies));
   152    return 0;
   153  }
   154  
   155  /***
   156   build & benchmark results
   157  
   158  BUILD COMMANDS FOR: nbody.gcc
   159  
   160  Thu Jul 27 22:22:05 PDT 2006
   161  
   162  /usr/bin/gcc -pipe -Wall -O3 -fomit-frame-pointer -funroll-loops -march=pentium4 -lm nbody.c -o nbody.gcc_run
   163  
   164  =================================================================
   165  COMMAND LINE (%A is single numeric argument):
   166  
   167  nbody.gcc_run %A
   168  
   169  N=200000 2000000 20000000
   170  PROGRAM OUTPUT
   171  ==============
   172  -0.169075164
   173  -0.169031665
   174  ***/