[Courgette] Initial Implementation of LabelManager

This is part of the effort to reduce Courgette's peak memory. Main changes:
- Moving Label to image_utils.h, and change Label::count_ from int to int32.
- Adding utility class ConsecutiveRangeVisitor, with tests.
- Adding LabelManager, with tests.
The new code is not yet used in production.

Review URL: https://codereview.chromium.org/1491703003

Cr-Commit-Position: refs/heads/master@{#363688}

1 files changed, 64 insertions, 0 deletions

diff --git a/courgette/label_manager.h b/courgette/label_manager.h
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+++ b/courgette/label_manager.h
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+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COURGETTE_LABEL_MANAGER_H_
+#define COURGETTE_LABEL_MANAGER_H_
+
+#include <vector>
+
+#include "base/macros.h"
+#include "courgette/image_utils.h"
+
+namespace courgette {
+
+// A container to store and manage Label instances. A key consideration is peak
+// memory usage reduction. To this end we preallocate Label instances in bulk,
+// and carefully control transient memory usage when initializing Labels.
+class LabelManager {
+ public:
+  // An adaptor to sequentially traverse multiple RVAs. This is useful for RVA
+  // translation without extra storage. For example, we might have a stored list
+  // of RVA locations, but we want to traverse the matching RVA targets.
+  class RvaVisitor {
+   public:
+    virtual ~RvaVisitor();
+
+    // Returns the number of remaining RVAs to visit.
+    virtual size_t Remaining() const = 0;
+
+    // Returns the current RVA.
+    virtual RVA Get() const = 0;
+
+    // Advances to the next RVA.
+    virtual void Next() = 0;
+  };
+
+  LabelManager();
+  virtual ~LabelManager();
+
+  // Initializes |labels_| using RVAs from |rva_visitor|. Each distinct RVA from
+  // |rva_visitor| yields a Label with |rva_| assigned as the RVA, and |count_|
+  // assigned as the repeat.
+  void Read(RvaVisitor* rva_visitor);
+
+  // Removes |labels_| elements whose |count_| is less than |count_threshold|.
+  void RemoveUnderusedLabels(int32 count_threshold);
+
+  // Efficiently searches for a Label that targets |rva|. Returns the pointer to
+  // the stored Label instance if found, or null otherwise.
+  Label* Find(RVA rva);
+
+  // TODO(huangs): Move AssignRemainingIndexes() here.
+
+ protected:
+  // The main list of Label instances, sorted by the |rva_| member.
+  std::vector<Label> labels_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(LabelManager);
+};
+
+}  // namespace courgette
+
+#endif  // COURGETTE_LABEL_MANAGER_H_