common: Add functions for comparing geoms and pointers

The loop_find() function needs a fallback comparison function to use
if no other comparison function was provided. This commit adds a
comparison function that compares two pointers.
Further, this commit adds a function that calculates the intersecting
area of two geometries.

diff --git a/common.c b/common.c
new file mode 100644 (file)
index 0000000..2c6058d
--- /dev/null
+++ b/common.c
@@ -0,0 +1,56 @@
+#include "common.h"
+
+#ifndef MIN
+#define MIN(X,Y) ((X) < (Y) ? (X) : (Y))
+#endif /* !defined(MIN) */
+
+#ifndef MAX
+#define MAX(X,Y) ((X) > (Y) ? (X) : (Y))
+#endif /* !defined(MAX) */
+
+int cmp_pointer(void *left, void *right)
+{
+       return(left == right);
+}
+
+int geom_intersects(struct geom *first, struct geom *second)
+{
+       int top;
+       int bottom;
+       int left;
+       int right;
+       int width;
+       int height;
+
+       /*
+        *           left
+        *           |   right
+        *           |   |
+        *           v   v
+        *    +----------+
+        *    |          |
+        *    |      +---+------+ <-- top
+        *    |      |   |      |
+        *    +------+---+      | <-- bottom
+        *           |          |
+        *           +----------+
+        *
+        * This function calculated the area of the intersection of
+        * the two rectangles. If the area is zero, the rectangles
+        * do not intersect.
+        */
+
+       top    = MAX(first->y,
+                    second->y);
+       bottom = MIN(first->y  + first->h,
+                    second->y + second->h);
+       left   = MAX(first->x,
+                    second->x);
+       right  = MIN(first->x  + first->w,
+                    second->x + second->w);
+
+       width  = MAX(0, right - left);
+       height = MAX(0, bottom - top);
+
+       return(width * height);
+}

diff --git a/common.h b/common.h
index 3bb5368bde669c36ad45a487c2880a60fceabdac..e041a23fa05686154979fbf700570a61f48470c6 100644 (file)
--- a/common.h
+++ b/common.h
@@ -8,4 +8,14 @@ struct geom {
        unsigned int h;
 };
 
+#ifndef FALSE
+#define FALSE 0
+#endif
+#ifndef TRUE
+#define TRUE  (!FALSE)
+#endif
+
+int cmp_pointer(void *left, void *right);
+int geom_intersects(struct geom *left, struct geom *right);
+
 #endif /* COMMON_H */