Generate random points on a 10-sphere

randomsphere.c

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

double random_uniform(){
  return ((double)rand()) / ((double)RAND_MAX);
}

double random_normal(){
  double u, v, s;

  do{
    u = 2 * random_uniform() - 1;
    v = 2 * random_uniform() - 1;
    s = u * u + v * v;
  } while(s >= 1);

  return u * sqrt(-2 * log(s) / s); 
}

void random_sphere(int n, double *data){
  double tot = 0;

  for(int i = 0; i < n; i++){
    double x = random_normal();
    tot += x * x;

    data[i] = x;
  }
  
  double norm = sqrt(tot);
  for(int i = 0; i < n; i++){
    data[i] /= norm;
  } 
}

#define DIM 10

int main(){
  double coords[DIM];

  srand(time(NULL) ^ getpid());

  random_sphere(DIM, coords); 

  for(int i = 0; i < DIM; i++){
    printf("%G", coords[i]);
    if (i == DIM - 1){
      printf("\n"); 
    } else {
      printf(" "); 
    }
  }

  return 0;
}