Changing back to the standard

Author: Gathros

chapters/computational_geometry/gift_wrapping/graham_scan/code/c/graham.c

@@ -1,5 +1,4 @@
 #include <math.h>
-#include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -22,8 +21,8 @@ int cmp_points(const void *a, const void *b) {
     }
 }
 
-bool is_left_of(struct point a, struct point b, struct point c) {
-    return (b.x - a.x) * (c.y - a.y) < (b.y - a.y) * (c.x - a.x);
+double ccw(struct point a, struct point b, struct point c) {
+    return (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);
 }
 
 double polar_angle(struct point origin, struct point p) {
@@ -73,7 +72,7 @@ size_t graham_scan(struct point *points, size_t size) {
 
     size_t m = 1;
     for (size_t i = 2; i <= size; ++i) {
-        while (is_left_of(tmp_points[m - 1], tmp_points[m], tmp_points[i])) {
+        while (ccw(tmp_points[m - 1], tmp_points[m], tmp_points[i]) <= 0) {
             if (m > 1) {
                 m--;
                 continue;