1 files changed, 26 insertions, 0 deletions
diff --git a/src/mbgl/style/expression/get_covering_stops.cpp b/src/mbgl/style/expression/get_covering_stops.cpp
new file mode 100644
index 0000000000..c9f87d93ac
--- /dev/null
+++ b/src/mbgl/style/expression/get_covering_stops.cpp
@@ -0,0 +1,26 @@
+#include <mbgl/style/expression/get_covering_stops.hpp>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+Range<float> getCoveringStops(const std::map<double, std::unique_ptr<Expression>>& stops,
+                              const double lower, const double upper) {
+    assert(!stops.empty());
+    auto minIt = stops.lower_bound(lower);
+    auto maxIt = stops.lower_bound(upper);
+
+    // lower_bound yields first element >= lowerZoom, but we want the *last*
+    // element <= lowerZoom, so if we found a stop > lowerZoom, back up by one.
+    if (minIt != stops.begin() && minIt != stops.end() && minIt->first > lower) {
+        minIt--;
+    }
+    return Range<float> {
+        static_cast<float>(minIt == stops.end() ? stops.rbegin()->first : minIt->first),
+        static_cast<float>(maxIt == stops.end() ? stops.rbegin()->first : maxIt->first)
+    };
+}
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl