From d35ef72a99a300db673fc493d11e991f54e287f7 Mon Sep 17 00:00:00 2001
From: Dane Springmeyer <dane@mapbox.com>
Date: Tue, 26 Apr 2016 17:15:14 -0700
Subject: [PATCH] fix 'runtime error: left shift of negative value -12' error -
 refs #227

---
 mvt.cc | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mvt.cc b/mvt.cc
index f1c0357f..423566da 100644
--- a/mvt.cc
+++ b/mvt.cc
@@ -5,6 +5,7 @@
 #include <map>
 #include <zlib.h>
 #include "mvt.hh"
+#include "protozero/varint.hpp"
 #include "protozero/pbf_reader.hpp"
 #include "protozero/pbf_writer.hpp"
 
@@ -332,8 +333,8 @@ std::string mvt_tile::encode() {
 					int dx = wwx - px;
 					int dy = wwy - py;
 
-					geometry.push_back((dx << 1) ^ (dx >> 31));
-					geometry.push_back((dy << 1) ^ (dy >> 31));
+					geometry.push_back(protozero::encode_zigzag32(dx));
+					geometry.push_back(protozero::encode_zigzag32(dy));
 
 					px = wwx;
 					py = wwy;