more primitive way to reduce size

qmk_firmware/keyboards/keyball/lib/keyball/keyball.c

@@ -65,6 +65,13 @@ static int16_t add16(int16_t a, int16_t b) {
     return r;
 }
 
+// divmod16 divides *v by div, return the quotient, and put the remainder in *v.
+static int16_t divmod16(int16_t *v, int16_t div) {
+    int16_t r = *v / div;
+    *v -= r * div;
+    return r;
+}
+
 // clip2int8 clips an integer fit into int8_t.
 static inline int8_t clip2int8(int16_t v) {
     return (v) < -127 ? -127 : (v) > 127 ? 127 : (int8_t)v;
@@ -171,11 +178,9 @@ static void motion_to_mouse_move(keyball_motion_t *m, report_mouse_t *r, bool is
 
 static void motion_to_mouse_scroll(keyball_motion_t *m, report_mouse_t *r, bool is_left) {
     // consume motion of trackball.
-    uint8_t div = keyball_get_scroll_div() - 1;
-    int16_t x   = m->x / (1 << div);
-    m->x -= x << div;
-    int16_t y = m->y / (1 << div);
-    m->y -= y << div;
+    int16_t div = 1 << (keyball_get_scroll_div() - 1);
+    int16_t x = divmod16(&m->x, div);
+    int16_t y = divmod16(&m->y, div);
 
     // apply to mouse report.
 #if KEYBALL_MODEL == 61 || KEYBALL_MODEL == 39 || KEYBALL_MODEL == 147 || KEYBALL_MODEL == 44