fast_path.c

//courtesy: MIT Open Courseware (https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-172-performance-engineering-of-software-systems-fall-2018/lecture-slides/MIT6_172F18_lec2.pdf)
#include <stdbool.h>
#include <math.h>

typedef struct{
  double x;   //x-coordinate
  double y;   //y-coordinate
  double z;   //z-coordinate
  double r;   // radius of the ball
} ball_t;

double square (double x){
   return x * x;
}

bool collides(ball_t *b1, ball_t *b2){
  if((abs(b1->x - b2->x) > abs(b1->r + b2->r)) || ((abs(b1->y - b2->y) > abs(b1->r + b2->r)) || ((abs(b1->z - b2->z) > abs(b1->r + b2->r))){
    return false;
  }
  double squared_distance = square(b1->x - b2->x) + square(b1->y - b2->y) + square(b1->z - b2->z);
  return squared_distance <= square(b1->r + b2->r);
}