From e07a4dd51b2dfbe3a57f3be36ecba1b3c9c213b2 Mon Sep 17 00:00:00 2001
From: Eric Fischer <enf@pobox.com>
Date: Thu, 18 Jan 2018 12:10:47 -0800
Subject: [PATCH] Fix out-of-bounds error when no threads were needed for a
 zoom level

---
 .travis.yml                                        |  2 +-
 tests/onefeature/-zg_--drop-densest-as-needed.json | 13 +++++++++++++
 tests/onefeature/in.json                           |  1 +
 tile.cpp                                           |  3 +++
 4 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 tests/onefeature/-zg_--drop-densest-as-needed.json
 create mode 100644 tests/onefeature/in.json

diff --git a/.travis.yml b/.travis.yml
index cd905ff..c44d170 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -43,7 +43,7 @@ matrix:
     # debug+leak+address-sanitizer build
     - os: linux
       compiler: clang
-      env: CLANG_VERSION='3.8.0' BUILDTYPE=Debug ASAN_OPTIONS=detect_leaks=1 CC="clang-3.8" CXX="clang++-3.8" CXXFLAGS="-fsanitize=address" CFLAGS="-fsanitize=address" LDFLAGS="-fsanitize=address" FEWER=true
+      env: CLANG_VERSION='3.8.0' BUILDTYPE=Debug ASAN_OPTIONS=detect_leaks=1 CC="clang-3.8" CXX="clang++-3.8" CXXFLAGS="-fsanitize=address,undefined" CFLAGS="-fsanitize=address,undefined" LDFLAGS="-fsanitize=address,undefined" FEWER=true
       addons:
         apt:
           sources: ['ubuntu-toolchain-r-test' ]
diff --git a/tests/onefeature/-zg_--drop-densest-as-needed.json b/tests/onefeature/-zg_--drop-densest-as-needed.json
new file mode 100644
index 0000000..da418e6
--- /dev/null
+++ b/tests/onefeature/-zg_--drop-densest-as-needed.json
@@ -0,0 +1,13 @@
+{ "type": "FeatureCollection", "properties": {
+"bounds": "-180.000000,0.800000,180.000000,1.000000",
+"center": "-179.989014,1.000000,14",
+"description": "tests/onefeature/-zg_--drop-densest-as-needed.json.check.mbtiles",
+"format": "pbf",
+"json": "{\"vector_layers\": [ { \"id\": \"in\", \"description\": \"\", \"minzoom\": 0, \"maxzoom\": 14, \"fields\": {} } ],\"tilestats\": {\"layerCount\": 1,\"layers\": [{\"layer\": \"in\",\"count\": 1,\"geometry\": \"LineString\",\"attributeCount\": 0,\"attributes\": []}]}}",
+"maxzoom": "14",
+"minzoom": "0",
+"name": "tests/onefeature/-zg_--drop-densest-as-needed.json.check.mbtiles",
+"type": "overlay",
+"version": "2"
+}, "features": [
+] }
diff --git a/tests/onefeature/in.json b/tests/onefeature/in.json
new file mode 100644
index 0000000..4d140e9
--- /dev/null
+++ b/tests/onefeature/in.json
@@ -0,0 +1 @@
+{"":"","":[{"":"","":{"":[]},"":{"":""}},{"":"","type":"LineString","coordinates":[[1000,0.8],[900,1]]}
diff --git a/tile.cpp b/tile.cpp
index 3119c32..18b09d8 100644
--- a/tile.cpp
+++ b/tile.cpp
@@ -2363,6 +2363,9 @@ int traverse_zooms(int *geomfd, off_t *geom_size, char *metabase, char *stringpo
 		if (threads >= (1U << 30)) {
 			threads = 1U << 30;
 		}
+		if (threads < 1) {
+			threads = 1;
+		}
 
 		// Assign temporary files to threads