AP_Math: correct variable init and remove define in polygon

libraries/AP_Math/polygon.cpp

@@ -43,19 +43,16 @@ bool Polygon_outside(const Vector2<T> &P, const Vector2<T> *V, unsigned n)
         if ((V[i].y > P.y) == (V[j].y > P.y)) {
             continue;
         }
-        int32_t dx1, dx2, dy1, dy2;
-        dx1 = P.x - V[i].x;
-        dx2 = V[j].x - V[i].x;
-        dy1 = P.y - V[i].y;
-        dy2 = V[j].y - V[i].y;
-        int8_t dx1s, dx2s, dy1s, dy2s, m1, m2;
-#define sign(x) ((x)<0 ? -1 : 1)
-        dx1s = sign(dx1);
-        dx2s = sign(dx2);
-        dy1s = sign(dy1);
-        dy2s = sign(dy2);
-        m1 = dx1s * dy2s;
-        m2 = dx2s * dy1s;
+        const int32_t dx1 = P.x - V[i].x;
+        const int32_t dx2 = V[j].x - V[i].x;
+        const int32_t dy1 = P.y - V[i].y;
+        const int32_t dy2 = V[j].y - V[i].y;
+        const int8_t dx1s = (dx1 < 0) ? -1 : 1;
+        const int8_t dx2s = (dx2 < 0) ? -1 : 1;
+        const int8_t dy1s = (dy1 < 0) ? -1 : 1;
+        const int8_t dy2s = (dy2 < 0) ? -1 : 1;
+        const int8_t m1 = dx1s * dy2s;
+        const int8_t m2 = dx2s * dy1s;
         // we avoid the 64 bit multiplies if we can based on sign checks.
         if (dy2 < 0) {
             if (m1 > m2) {