From a4cda4ce208a0601bbd9cd900e3b51bfb3ac7de2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Konstantin=20Ka=CC=88fer?= <mail@kkaefer.com>
Date: Fri, 21 Mar 2014 13:17:42 +0100
Subject: [PATCH] fix Tile::parent() for negative x coords

---
 include/llmr/map/tile.hpp |  4 ++--
 src/map/tile.cpp          | 15 +++++++--------
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/include/llmr/map/tile.hpp b/include/llmr/map/tile.hpp
index 2ae1a64fe..0857cf17b 100644
--- a/include/llmr/map/tile.hpp
+++ b/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;
diff --git a/src/map/tile.cpp b/src/map/tile.cpp
index 163aa60af..e619c32bf 100644
--- a/src/map/tile.cpp
+++ b/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{
+        static_cast<int8_t>(parent_z),
+        static_cast<int32_t>(floor((float)x / dim)),
+        static_cast<int32_t>(y / dim)
+    };
 }
 
 std::forward_list<Tile::ID> Tile::ID::children(int32_t child_z) const {