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diff --git a/rangeset.h b/rangeset.h
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+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <stddef.h>
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include <android-base/logging.h>
+#include <android-base/parseint.h>
+#include <android-base/stringprintf.h>
+#include <android-base/strings.h>
+
+using Range = std::pair<size_t, size_t>;
+
+class RangeSet {
+ public:
+  RangeSet() : blocks_(0) {}
+
+  explicit RangeSet(std::vector<Range>&& pairs) {
+    CHECK_NE(pairs.size(), static_cast<size_t>(0)) << "Invalid number of tokens";
+
+    // Sanity check the input.
+    size_t result = 0;
+    for (const auto& range : pairs) {
+      CHECK_LT(range.first, range.second)
+          << "Empty or negative range: " << range.first << ", " << range.second;
+      size_t sz = range.second - range.first;
+      CHECK_LE(result, SIZE_MAX - sz) << "RangeSet size overflow";
+      result += sz;
+    }
+
+    ranges_ = pairs;
+    blocks_ = result;
+  }
+
+  static RangeSet Parse(const std::string& range_text) {
+    std::vector<std::string> pieces = android::base::Split(range_text, ",");
+    CHECK_GE(pieces.size(), static_cast<size_t>(3)) << "Invalid range text: " << range_text;
+
+    size_t num;
+    CHECK(android::base::ParseUint(pieces[0], &num, static_cast<size_t>(INT_MAX)))
+        << "Failed to parse the number of tokens: " << range_text;
+
+    CHECK_NE(num, static_cast<size_t>(0)) << "Invalid number of tokens: " << range_text;
+    CHECK_EQ(num % 2, static_cast<size_t>(0)) << "Number of tokens must be even: " << range_text;
+    CHECK_EQ(num, pieces.size() - 1) << "Mismatching number of tokens: " << range_text;
+
+    std::vector<Range> pairs;
+    for (size_t i = 0; i < num; i += 2) {
+      size_t first;
+      CHECK(android::base::ParseUint(pieces[i + 1], &first, static_cast<size_t>(INT_MAX)));
+      size_t second;
+      CHECK(android::base::ParseUint(pieces[i + 2], &second, static_cast<size_t>(INT_MAX)));
+
+      pairs.emplace_back(first, second);
+    }
+
+    return RangeSet(std::move(pairs));
+  }
+
+  std::string ToString() const {
+    if (ranges_.empty()) {
+      return "";
+    }
+    std::string result = std::to_string(ranges_.size() * 2);
+    for (const auto& r : ranges_) {
+      result += android::base::StringPrintf(",%zu,%zu", r.first, r.second);
+    }
+
+    return result;
+  }
+
+  // Get the block number for the i-th (starting from 0) block in the RangeSet.
+  size_t GetBlockNumber(size_t idx) const {
+    CHECK_LT(idx, blocks_) << "Out of bound index " << idx << " (total blocks: " << blocks_ << ")";
+
+    for (const auto& range : ranges_) {
+      if (idx < range.second - range.first) {
+        return range.first + idx;
+      }
+      idx -= (range.second - range.first);
+    }
+
+    CHECK(false) << "Failed to find block number for index " << idx;
+    return 0;  // Unreachable, but to make compiler happy.
+  }
+
+  // RangeSet has half-closed half-open bounds. For example, "3,5" contains blocks 3 and 4. So "3,5"
+  // and "5,7" are not overlapped.
+  bool Overlaps(const RangeSet& other) const {
+    for (const auto& range : ranges_) {
+      size_t start = range.first;
+      size_t end = range.second;
+      for (const auto& other_range : other.ranges_) {
+        size_t other_start = other_range.first;
+        size_t other_end = other_range.second;
+        // [start, end) vs [other_start, other_end)
+        if (!(other_start >= end || start >= other_end)) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  // size() gives the number of Range's in this RangeSet.
+  size_t size() const {
+    return ranges_.size();
+  }
+
+  // blocks() gives the number of all blocks in this RangeSet.
+  size_t blocks() const {
+    return blocks_;
+  }
+
+  // We provide const iterators only.
+  std::vector<Range>::const_iterator cbegin() const {
+    return ranges_.cbegin();
+  }
+
+  std::vector<Range>::const_iterator cend() const {
+    return ranges_.cend();
+  }
+
+  // Need to provide begin()/end() since range-based loop expects begin()/end().
+  std::vector<Range>::const_iterator begin() const {
+    return ranges_.cbegin();
+  }
+
+  std::vector<Range>::const_iterator end() const {
+    return ranges_.cend();
+  }
+
+  // Reverse const iterators for MoveRange().
+  std::vector<Range>::const_reverse_iterator crbegin() const {
+    return ranges_.crbegin();
+  }
+
+  std::vector<Range>::const_reverse_iterator crend() const {
+    return ranges_.crend();
+  }
+
+  const Range& operator[](size_t i) const {
+    return ranges_[i];
+  }
+
+  bool operator==(const RangeSet& other) const {
+    // The orders of Range's matter. "4,1,5,8,10" != "4,8,10,1,5".
+    return (ranges_ == other.ranges_);
+  }
+
+  bool operator!=(const RangeSet& other) const {
+    return ranges_ != other.ranges_;
+  }
+
+ protected:
+  // Actual limit for each value and the total number are both INT_MAX.
+  std::vector<Range> ranges_;
+  size_t blocks_;
+};
+
+static constexpr size_t kBlockSize = 4096;
+
+// The class is a sorted version of a RangeSet; and it's useful in imgdiff to split the input
+// files when we're handling large zip files. Specifically, we can treat the input file as a
+// continuous RangeSet (i.e. RangeSet("0-99") for a 100 blocks file); and break it down into
+// several smaller chunks based on the zip entries.
+
+// For example, [source: 0-99] can be split into
+// [split_src1: 10-29]; [split_src2: 40-49, 60-69]; [split_src3: 70-89]
+// Here "10-29" simply means block 10th to block 29th with respect to the original input file.
+// Also, note that the split sources should be mutual exclusive, but they don't need to cover
+// every block in the original source.
+class SortedRangeSet : public RangeSet {
+ public:
+  SortedRangeSet() {}
+
+  // Ranges in the the set should be mutually exclusive; and they're sorted by the start block.
+  explicit SortedRangeSet(std::vector<Range>&& pairs) : RangeSet(std::move(pairs)) {
+    std::sort(ranges_.begin(), ranges_.end());
+  }
+
+  void Insert(const Range& to_insert) {
+    SortedRangeSet rs({ to_insert });
+    Insert(rs);
+  }
+
+  // Insert the input SortedRangeSet; keep the ranges sorted and merge the overlap ranges.
+  void Insert(const SortedRangeSet& rs) {
+    if (rs.size() == 0) {
+      return;
+    }
+    // Merge and sort the two RangeSets.
+    std::vector<Range> temp = std::move(ranges_);
+    std::copy(rs.begin(), rs.end(), std::back_inserter(temp));
+    std::sort(temp.begin(), temp.end());
+
+    Clear();
+    // Trim overlaps and insert the result back to ranges_.
+    Range to_insert = temp.front();
+    for (auto it = temp.cbegin() + 1; it != temp.cend(); it++) {
+      if (it->first <= to_insert.second) {
+        to_insert.second = std::max(to_insert.second, it->second);
+      } else {
+        ranges_.push_back(to_insert);
+        blocks_ += (to_insert.second - to_insert.first);
+        to_insert = *it;
+      }
+    }
+    ranges_.push_back(to_insert);
+    blocks_ += (to_insert.second - to_insert.first);
+  }
+
+  void Clear() {
+    blocks_ = 0;
+    ranges_.clear();
+  }
+
+  using RangeSet::Overlaps;
+  bool Overlaps(size_t start, size_t len) const {
+    RangeSet rs({ { start / kBlockSize, (start + len - 1) / kBlockSize + 1 } });
+    return Overlaps(rs);
+  }
+
+  // Compute the block range the file occupies, and insert that range.
+  void Insert(size_t start, size_t len) {
+    Range to_insert{ start / kBlockSize, (start + len - 1) / kBlockSize + 1 };
+    Insert(to_insert);
+  }
+
+  // Given an offset of the file, checks if the corresponding block (by considering the file as
+  // 0-based continuous block ranges) is covered by the SortedRangeSet. If so, returns the offset
+  // within this SortedRangeSet.
+  //
+  // For example, the 4106-th byte of a file is from block 1, assuming a block size of 4096-byte.
+  // The mapped offset within a SortedRangeSet("1-9 15-19") is 10.
+  //
+  // An offset of 65546 falls into the 16-th block in a file. Block 16 is contained as the 10-th
+  // item in SortedRangeSet("1-9 15-19"). So its data can be found at offset 40970 (i.e. 4096 * 10
+  // + 10) in a range represented by this SortedRangeSet.
+  size_t GetOffsetInRangeSet(size_t old_offset) const {
+    size_t old_block_start = old_offset / kBlockSize;
+    size_t new_block_start = 0;
+    for (const auto& range : ranges_) {
+      // Find the index of old_block_start.
+      if (old_block_start >= range.second) {
+        new_block_start += (range.second - range.first);
+      } else if (old_block_start >= range.first) {
+        new_block_start += (old_block_start - range.first);
+        return (new_block_start * kBlockSize + old_offset % kBlockSize);
+      } else {
+        CHECK(false) << "block_start " << old_block_start
+                     << " is missing between two ranges: " << this->ToString();
+        return 0;
+      }
+    }
+    CHECK(false) << "block_start " << old_block_start
+                 << " exceeds the limit of current RangeSet: " << this->ToString();
+    return 0;
+  }
+};
\ No newline at end of file