diff --git a/extent_ranges.cc b/extent_ranges.cc
new file mode 100755
index 0000000..a8836c9
--- /dev/null
+++ b/extent_ranges.cc
@@ -0,0 +1,219 @@
+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "update_engine/extent_ranges.h"
+
+#include <set>
+#include <utility>
+#include <vector>
+
+#include <base/logging.h>
+
+using std::max;
+using std::min;
+using std::set;
+using std::vector;
+
+namespace chromeos_update_engine {
+
+bool ExtentRanges::ExtentsOverlapOrTouch(const Extent& a, const Extent& b) {
+  if (a.start_block() == b.start_block())
+    return true;
+  if (a.start_block() < b.start_block()) {
+    return a.start_block() + a.num_blocks() >= b.start_block();
+  } else {
+    return b.start_block() + b.num_blocks() >= a.start_block();
+  }
+}
+
+bool ExtentRanges::ExtentsOverlap(const Extent& a, const Extent& b) {
+  if (a.start_block() == b.start_block())
+    return true;
+  if (a.start_block() < b.start_block()) {
+    return a.start_block() + a.num_blocks() > b.start_block();
+  } else {
+    return b.start_block() + b.num_blocks() > a.start_block();
+  }
+}
+
+void ExtentRanges::AddBlock(uint64_t block) {
+  AddExtent(ExtentForRange(block, 1));
+}
+
+void ExtentRanges::SubtractBlock(uint64_t block) {
+  SubtractExtent(ExtentForRange(block, 1));
+}
+
+namespace {
+
+Extent UnionOverlappingExtents(const Extent& first, const Extent& second) {
+  uint64_t start = min(first.start_block(), second.start_block());
+  uint64_t end = max(first.start_block() + first.num_blocks(),
+                     second.start_block() + second.num_blocks());
+  return ExtentForRange(start, end - start);
+}
+  
+}  // namespace {}
+
+void ExtentRanges::AddExtent(Extent extent) {
+  if (extent.num_blocks() == 0)
+    return;
+
+  ExtentSet::iterator begin_del = extent_set_.end();
+  ExtentSet::iterator end_del = extent_set_.end();
+  uint64_t del_blocks = 0;
+  for (ExtentSet::iterator it = extent_set_.begin(), e = extent_set_.end();
+       it != e; ++it) {
+    if (ExtentsOverlapOrTouch(*it, extent)) {
+      end_del = it;
+      ++end_del;
+      del_blocks += it->num_blocks();
+      if (begin_del == extent_set_.end())
+        begin_del = it;
+
+      extent = UnionOverlappingExtents(extent, *it);
+    }
+  }
+  extent_set_.erase(begin_del, end_del);
+  extent_set_.insert(extent);
+  blocks_ -= del_blocks;
+  blocks_ += extent.num_blocks();
+}
+
+namespace {
+// Returns base - subtractee (set subtraction).
+ExtentRanges::ExtentSet SubtractOverlappingExtents(const Extent& base,
+                                                   const Extent& subtractee) {
+  ExtentRanges::ExtentSet ret;
+  if (subtractee.start_block() > base.start_block()) {
+    ret.insert(ExtentForRange(base.start_block(),
+                              subtractee.start_block() - base.start_block()));
+  }
+  uint64_t base_end = base.start_block() + base.num_blocks();
+  uint64_t subtractee_end = subtractee.start_block() + subtractee.num_blocks();
+  if (base_end > subtractee_end) {
+    ret.insert(ExtentForRange(subtractee_end, base_end - subtractee_end));
+  }
+  return ret;
+}
+}  // namespace {}
+
+void ExtentRanges::SubtractExtent(const Extent& extent) {
+  if (extent.num_blocks() == 0)
+    return;
+
+  ExtentSet::iterator begin_del = extent_set_.end();
+  ExtentSet::iterator end_del = extent_set_.end();
+  uint64_t del_blocks = 0;
+  ExtentSet new_extents;
+  for (ExtentSet::iterator it = extent_set_.begin(), e = extent_set_.end();
+       it != e; ++it) {
+    if (!ExtentsOverlap(*it, extent))
+      continue;
+    
+    if (begin_del == extent_set_.end())
+      begin_del = it;
+    end_del = it;
+    ++end_del;
+    
+    del_blocks += it->num_blocks();
+
+    ExtentSet subtraction = SubtractOverlappingExtents(*it, extent);
+    for (ExtentSet::iterator jt = subtraction.begin(), je = subtraction.end();
+         jt != je; ++jt) {
+      new_extents.insert(*jt);
+      del_blocks -= jt->num_blocks();
+    }
+  }
+  extent_set_.erase(begin_del, end_del);
+  extent_set_.insert(new_extents.begin(), new_extents.end());
+  blocks_ -= del_blocks;
+}
+
+void ExtentRanges::AddRanges(const ExtentRanges& ranges) {
+  for (ExtentSet::const_iterator it = ranges.extent_set_.begin(),
+           e = ranges.extent_set_.end(); it != e; ++it) {
+    AddExtent(*it);
+  }
+}
+
+void ExtentRanges::SubtractRanges(const ExtentRanges& ranges) {
+  for (ExtentSet::const_iterator it = ranges.extent_set_.begin(),
+           e = ranges.extent_set_.end(); it != e; ++it) {
+    SubtractExtent(*it);
+  }
+}
+
+void ExtentRanges::AddExtents(const vector<Extent>& extents) {
+  for (vector<Extent>::const_iterator it = extents.begin(), e = extents.end();
+       it != e; ++it) {
+    AddExtent(*it);
+  }
+}
+
+void ExtentRanges::SubtractExtents(const vector<Extent>& extents) {
+  for (vector<Extent>::const_iterator it = extents.begin(), e = extents.end();
+       it != e; ++it) {
+    SubtractExtent(*it);
+  }
+}
+
+void ExtentRanges::AddRepeatedExtents(
+    const ::google::protobuf::RepeatedPtrField<Extent> &exts) {
+  for (int i = 0, e = exts.size(); i != e; ++i) {
+    AddExtent(exts.Get(i));
+  }
+}
+
+void ExtentRanges::SubtractRepeatedExtents(
+    const ::google::protobuf::RepeatedPtrField<Extent> &exts) {
+  for (int i = 0, e = exts.size(); i != e; ++i) {
+    SubtractExtent(exts.Get(i));
+  }
+}
+
+void ExtentRanges::Dump() const {
+  LOG(INFO) << "ExtentRanges Dump. blocks: " << blocks_;
+  for (ExtentSet::const_iterator it = extent_set_.begin(),
+           e = extent_set_.end();
+       it != e; ++it) {
+    LOG(INFO) << "{" << it->start_block() << ", " << it->num_blocks() << "}";
+  }
+}
+
+Extent ExtentForRange(uint64_t start_block, uint64_t num_blocks) {
+  Extent ret;
+  ret.set_start_block(start_block);
+  ret.set_num_blocks(num_blocks);
+  return ret;
+}
+
+std::vector<Extent> ExtentRanges::GetExtentsForBlockCount(
+    uint64_t count) const {
+  vector<Extent> out;
+  if (count == 0)
+    return out;
+  uint64_t out_blocks = 0;
+  CHECK(count <= blocks_);
+  for (ExtentSet::const_iterator it = extent_set_.begin(),
+           e = extent_set_.end();
+       it != e; ++it) {
+    const uint64_t blocks_needed = count - out_blocks;
+    const Extent& extent = *it;
+    out.push_back(extent);
+    out_blocks += extent.num_blocks();
+    if (extent.num_blocks() < blocks_needed)
+      continue;
+    if (extent.num_blocks() == blocks_needed)
+      break;
+    // If we get here, we just added the last extent needed, but it's too big
+    out_blocks -= extent.num_blocks();
+    out_blocks += blocks_needed;
+    out.back().set_num_blocks(blocks_needed);
+    break;
+  }
+  return out;
+}
+
+}  // namespace chromeos_update_engine