Merge branch 'master' of github.com:mapbox/llmr-native

include/llmr/map/tile.hpp

@@ -18,7 +18,7 @@ public:
         int8_t z = 0;
         int32_t x = 0, y = 0;
 
-        inline ID(uint8_t z, uint32_t x, uint32_t y)
+        inline ID(int8_t z, int32_t x, int32_t y)
             : z(z), x(x), y(y) {
         }
 
@@ -31,7 +31,7 @@ public:
             return z == rhs.z && x == rhs.x && y == rhs.y;
         }
 
-        ID parent(int32_t z) const;
+        ID parent(int8_t z) const;
         void normalize();
         ID normalized() const;
         std::forward_list<ID> children(int32_t z) const;

src/map/tile.cpp

@@ -8,15 +8,14 @@ Tile::Tile(const ID& id)
     : id(id) {
 }
 
-Tile::ID Tile::ID::parent(int32_t parent_z) const {
+Tile::ID Tile::ID::parent(int8_t parent_z) const {
     assert(parent_z < z);
-    ID pos(z, x, y);
-    while (pos.z > parent_z) {
-        --pos.z;
-        pos.x = floor(pos.x / 2);
-        pos.y = floor(pos.y / 2);
-    }
-    return pos;
+    int32_t dim = pow(2, z - parent_z);
+    return Tile::ID{
+        parent_z,
+        (x >= 0 ? x : x - dim + 1) / dim,
+        y / dim
+    };
 }
 
 std::forward_list<Tile::ID> Tile::ID::children(int32_t child_z) const {