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diff --git a/src/support/space.h b/src/support/space.h
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+/*
+ * Copyright 2020 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef wasm_support_space_h
+#define wasm_support_space_h
+
+#include "utilities.h"
+#include <wasm.h>
+
+namespace wasm {
+
+struct DisjointSpans {
+  // A span of form [a, b), i.e., that does not include the end point.
+  struct Span {
+    Address left, right;
+
+    bool checkOverlap(const Span& other) const {
+      return !(left >= other.right || right <= other.left);
+    }
+  };
+
+  struct SortByLeft {
+    bool operator()(const Span& left, const Span& right) const {
+      return left.left < right.left ||
+             (left.left == right.left && left.right < right.right);
+    }
+  };
+
+  // The spans seen so far. Guaranteed to be disjoint.
+  std::set<Span, SortByLeft> spans;
+
+  // Adds an item and checks overlap while doing so, returning true if such
+  // overlap exists.
+  bool addAndCheckOverlap(Span span) {
+    // Insert the new span. We can then find its predecessor and successor.
+    // They are disjoint by assumption, so the question is then does the new
+    // span overlap with them, or not.
+    decltype(spans)::iterator iter;
+    bool inserted;
+    std::tie(iter, inserted) = spans.insert(span);
+    if (!inserted) {
+      // This exact span was already there, so there is definite overlap.
+      return true;
+    }
+    // Check predecessor and successor, if they exist.
+    if (iter != spans.begin() && std::prev(iter)->checkOverlap(span)) {
+      return true;
+    }
+    if (std::next(iter) != spans.end() && std::next(iter)->checkOverlap(span)) {
+      return true;
+    }
+    return false;
+  }
+
+  // Inefficient - mostly for testing.
+  void add(Span span) { addAndCheckOverlap(span); }
+
+  // Inefficient - mostly for testing.
+  bool checkOverlap(Span span) {
+    bool existsBefore = spans.find(span) != spans.end();
+    auto hasOverlap = addAndCheckOverlap(span);
+    if (!existsBefore) {
+      spans.erase(span);
+    }
+    return hasOverlap;
+  }
+};
+
+} // namespace wasm
+
+#endif // wasm_support_space_h