#define MAX_BRUSHFORBOX 16
-static int brushforbox_index = 0;
+static unsigned int brushforbox_index = 0;
+// note: this relies on integer overflow to be consistent with modulo
+// MAX_BRUSHFORBOX, or in other words, MAX_BRUSHFORBOX must be a power of two!
static colpointf_t brushforbox_point[MAX_BRUSHFORBOX*8];
static colplanef_t brushforbox_plane[MAX_BRUSHFORBOX*6];
static colbrushf_t brushforbox_brush[MAX_BRUSHFORBOX];