// C code for https://karthikkaranth.me/blog/generating-random-points-in-a-sphere/
// see HN discussion here https://news.ycombinator.com/item?id=17688599

// ============================== getpoint1.c ==============================
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

void getPoint(double v[]) {
  double d;
  do {
    v[0] = (rand()/(double)RAND_MAX)*2.0 - 1.0;
    v[1] = (rand()/(double)RAND_MAX)*2.0 - 1.0;
    v[2] = (rand()/(double)RAND_MAX)*2.0 - 1.0;
    d = v[0]*v[0] + v[1]*v[1] + v[2]*v[2];
  } while (d > 1.0);
}

int main(int argc, char *argv[]) {

  double v[3];
  for (int i=0; i<1e7; i++) {
    getPoint(v);
  }
  return 0;
}

// ============================== getpoint5.c ==============================
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

void getPoint(double vec[]) {
  double u = (rand()/(double)RAND_MAX);
  double v = (rand()/(double)RAND_MAX);
  double theta = u * 2.0 * M_PI;
  double phi = acos(2.0 * v - 1.0);
  double r = cbrt(rand()/(double)RAND_MAX);
  double sinTheta = sin(theta);
  double cosTheta = cos(theta);
  double sinPhi = sin(phi);
  double cosPhi = cos(phi);
  vec[0] = r * sinPhi * cosTheta;
  vec[1] = r * sinPhi * sinTheta;
  vec[2] = r * cosPhi;
}

int main(int argc, char *argv[]) {

  double vec[3];
  for (int i=0; i<1e7; i++) {
    getPoint(vec);
  }
  return 0;
}