diff --git a/tests/Android.mk b/tests/Android.mk
index 80eae8f..974aa0e 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -25,6 +25,7 @@
     libverifier \
     libminui \
     libotautil \
+    libupdater \
     libziparchive \
     libutils \
     libz \
@@ -35,6 +36,7 @@
     unit/asn1_decoder_test.cpp \
     unit/dirutil_test.cpp \
     unit/locale_test.cpp \
+    unit/rangeset_test.cpp \
     unit/sysutil_test.cpp \
     unit/zip_test.cpp \
     unit/ziputil_test.cpp
diff --git a/tests/unit/rangeset_test.cpp b/tests/unit/rangeset_test.cpp
new file mode 100644
index 0000000..e66da20
--- /dev/null
+++ b/tests/unit/rangeset_test.cpp
@@ -0,0 +1,84 @@
+/*
+ * 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.
+ */
+
+#include <signal.h>
+#include <sys/types.h>
+
+#include <vector>
+
+#include <gtest/gtest.h>
+
+#include "updater/rangeset.h"
+
+TEST(RangeSetTest, Parse_smoke) {
+  RangeSet rs = RangeSet::Parse("2,1,10");
+  ASSERT_EQ(static_cast<size_t>(1), rs.count);
+  ASSERT_EQ((std::vector<size_t>{ 1, 10 }), rs.pos);
+  ASSERT_EQ(static_cast<size_t>(9), rs.size);
+
+  RangeSet rs2 = RangeSet::Parse("4,15,20,1,10");
+  ASSERT_EQ(static_cast<size_t>(2), rs2.count);
+  ASSERT_EQ((std::vector<size_t>{ 15, 20, 1, 10 }), rs2.pos);
+  ASSERT_EQ(static_cast<size_t>(14), rs2.size);
+
+  // Leading zeros are fine. But android::base::ParseUint() doesn't like trailing zeros like "10 ".
+  ASSERT_EQ(rs, RangeSet::Parse(" 2, 1,   10"));
+  ASSERT_EXIT(RangeSet::Parse("2,1,10 "), ::testing::KilledBySignal(SIGABRT), "");
+}
+
+TEST(RangeSetTest, Parse_InvalidCases) {
+  // Insufficient number of tokens.
+  ASSERT_EXIT(RangeSet::Parse(""), ::testing::KilledBySignal(SIGABRT), "");
+  ASSERT_EXIT(RangeSet::Parse("2,1"), ::testing::KilledBySignal(SIGABRT), "");
+
+  // The first token (i.e. the number of following tokens) is invalid.
+  ASSERT_EXIT(RangeSet::Parse("a,1,1"), ::testing::KilledBySignal(SIGABRT), "");
+  ASSERT_EXIT(RangeSet::Parse("3,1,1"), ::testing::KilledBySignal(SIGABRT), "");
+  ASSERT_EXIT(RangeSet::Parse("-3,1,1"), ::testing::KilledBySignal(SIGABRT), "");
+  ASSERT_EXIT(RangeSet::Parse("2,1,2,3"), ::testing::KilledBySignal(SIGABRT), "");
+
+  // Invalid tokens.
+  ASSERT_EXIT(RangeSet::Parse("2,1,10a"), ::testing::KilledBySignal(SIGABRT), "");
+  ASSERT_EXIT(RangeSet::Parse("2,,10"), ::testing::KilledBySignal(SIGABRT), "");
+
+  // Empty or negative range.
+  ASSERT_EXIT(RangeSet::Parse("2,2,2"), ::testing::KilledBySignal(SIGABRT), "");
+  ASSERT_EXIT(RangeSet::Parse("2,2,1"), ::testing::KilledBySignal(SIGABRT), "");
+}
+
+TEST(RangeSetTest, Overlaps) {
+  RangeSet r1 = RangeSet::Parse("2,1,6");
+  RangeSet r2 = RangeSet::Parse("2,5,10");
+  ASSERT_TRUE(r1.Overlaps(r2));
+  ASSERT_TRUE(r2.Overlaps(r1));
+
+  r2 = RangeSet::Parse("2,6,10");
+  ASSERT_FALSE(r1.Overlaps(r2));
+  ASSERT_FALSE(r2.Overlaps(r1));
+
+  ASSERT_FALSE(RangeSet::Parse("2,3,5").Overlaps(RangeSet::Parse("2,5,7")));
+  ASSERT_FALSE(RangeSet::Parse("2,5,7").Overlaps(RangeSet::Parse("2,3,5")));
+}
+
+TEST(RangeSetTest, GetBlockNumber) {
+  RangeSet rs = RangeSet::Parse("2,1,10");
+  ASSERT_EQ(static_cast<size_t>(1), rs.GetBlockNumber(0));
+  ASSERT_EQ(static_cast<size_t>(6), rs.GetBlockNumber(5));
+  ASSERT_EQ(static_cast<size_t>(9), rs.GetBlockNumber(8));
+
+  // Out of bound.
+  ASSERT_EXIT(rs.GetBlockNumber(9), ::testing::KilledBySignal(SIGABRT), "");
+}
diff --git a/updater/blockimg.cpp b/updater/blockimg.cpp
index a1a5773..fc7a561 100644
--- a/updater/blockimg.cpp
+++ b/updater/blockimg.cpp
@@ -50,9 +50,10 @@
 
 #include "edify/expr.h"
 #include "error_code.h"
-#include "updater/install.h"
 #include "ota_io.h"
 #include "print_sha1.h"
+#include "updater/install.h"
+#include "updater/rangeset.h"
 #include "updater/updater.h"
 
 // Set this to 0 to interpret 'erase' transfers to mean do a
@@ -65,100 +66,10 @@
 static constexpr mode_t STASH_DIRECTORY_MODE = 0700;
 static constexpr mode_t STASH_FILE_MODE = 0600;
 
-struct RangeSet {
-  size_t count;  // Limit is INT_MAX.
-  size_t size;
-  std::vector<size_t> pos;  // Actual limit is INT_MAX.
-
-  // Get the block number for the ith(starting from 0) block in the range set.
-  int get_block(size_t idx) const {
-    if (idx >= size) {
-      LOG(ERROR) << "index: " << idx << " is greater than range set size: " << size;
-      return -1;
-    }
-    for (size_t i = 0; i < pos.size(); i += 2) {
-      if (idx < pos[i + 1] - pos[i]) {
-        return pos[i] + idx;
-      }
-      idx -= (pos[i + 1] - pos[i]);
-    }
-    return -1;
-  }
-};
-
 static CauseCode failure_type = kNoCause;
 static bool is_retry = false;
 static std::unordered_map<std::string, RangeSet> stash_map;
 
-static RangeSet parse_range(const std::string& range_text) {
-  RangeSet rs;
-
-  std::vector<std::string> pieces = android::base::Split(range_text, ",");
-  if (pieces.size() < 3) {
-    goto err;
-  }
-
-  size_t num;
-  if (!android::base::ParseUint(pieces[0], &num, static_cast<size_t>(INT_MAX))) {
-    goto err;
-  }
-
-  if (num == 0 || num % 2) {
-    goto err;  // must be even
-  } else if (num != pieces.size() - 1) {
-    goto err;
-  }
-
-  rs.pos.resize(num);
-  rs.count = num / 2;
-  rs.size = 0;
-
-  for (size_t i = 0; i < num; i += 2) {
-    if (!android::base::ParseUint(pieces[i + 1], &rs.pos[i], static_cast<size_t>(INT_MAX))) {
-      goto err;
-    }
-
-    if (!android::base::ParseUint(pieces[i + 2], &rs.pos[i + 1], static_cast<size_t>(INT_MAX))) {
-      goto err;
-    }
-
-    if (rs.pos[i] >= rs.pos[i + 1]) {
-      goto err;  // empty or negative range
-    }
-
-    size_t sz = rs.pos[i + 1] - rs.pos[i];
-    if (rs.size > SIZE_MAX - sz) {
-      goto err;  // overflow
-    }
-
-    rs.size += sz;
-  }
-
-  return rs;
-
-err:
-  LOG(ERROR) << "failed to parse range '" << range_text << "'";
-  exit(EXIT_FAILURE);
-}
-
-static bool range_overlaps(const RangeSet& r1, const RangeSet& r2) {
-  for (size_t i = 0; i < r1.count; ++i) {
-    size_t r1_0 = r1.pos[i * 2];
-    size_t r1_1 = r1.pos[i * 2 + 1];
-
-    for (size_t j = 0; j < r2.count; ++j) {
-      size_t r2_0 = r2.pos[j * 2];
-      size_t r2_1 = r2.pos[j * 2 + 1];
-
-      if (!(r2_0 >= r1_1 || r1_0 >= r2_1)) {
-        return true;
-      }
-    }
-  }
-
-  return false;
-}
-
 static int read_all(int fd, uint8_t* data, size_t size) {
     size_t so_far = 0;
     while (so_far < size) {
@@ -469,7 +380,7 @@
     return;
   }
 
-  RangeSet src = parse_range(params.tokens[pos++]);
+  RangeSet src = RangeSet::Parse(params.tokens[pos++]);
 
   RangeSet locs;
   // If there's no stashed blocks, content in the buffer is consecutive and has the same
@@ -483,17 +394,15 @@
     // Example: for the tokens <4,63946,63947,63948,63979> <4,6,7,8,39> <stashed_blocks>;
     // We want to print SHA-1 for the data in buffer[6], buffer[8], buffer[9] ... buffer[38];
     // this corresponds to the 32 src blocks #63946, #63948, #63949 ... #63978.
-    locs = parse_range(params.tokens[pos++]);
+    locs = RangeSet::Parse(params.tokens[pos++]);
     CHECK_EQ(src.size, locs.size);
     CHECK_EQ(locs.pos.size() % 2, static_cast<size_t>(0));
   }
 
   LOG(INFO) << "printing hash in hex for " << src.size << " source blocks";
   for (size_t i = 0; i < src.size; i++) {
-    int block_num = src.get_block(i);
-    CHECK_NE(block_num, -1);
-    int buffer_index = locs.get_block(i);
-    CHECK_NE(buffer_index, -1);
+    size_t block_num = src.GetBlockNumber(i);
+    size_t buffer_index = locs.GetBlockNumber(i);
     CHECK_LE((buffer_index + 1) * BLOCKSIZE, buffer.size());
 
     uint8_t digest[SHA_DIGEST_LENGTH];
@@ -512,8 +421,7 @@
   CHECK_EQ(src.size * BLOCKSIZE, buffer.size());
 
   for (size_t i = 0; i < src.size; i++) {
-    int block_num = src.get_block(i);
-    CHECK_NE(block_num, -1);
+    size_t block_num = src.GetBlockNumber(i);
 
     uint8_t digest[SHA_DIGEST_LENGTH];
     SHA1(buffer.data() + i * BLOCKSIZE, BLOCKSIZE, digest);
@@ -925,8 +833,8 @@
     // no source ranges, only stashes
     params.cpos++;
   } else {
-    RangeSet src = parse_range(params.tokens[params.cpos++]);
-    *overlap = range_overlaps(src, tgt);
+    RangeSet src = RangeSet::Parse(params.tokens[params.cpos++]);
+    *overlap = src.Overlaps(tgt);
 
     if (ReadBlocks(src, params.buffer, params.fd) == -1) {
       return -1;
@@ -937,7 +845,7 @@
       return 0;
     }
 
-    RangeSet locs = parse_range(params.tokens[params.cpos++]);
+    RangeSet locs = RangeSet::Parse(params.tokens[params.cpos++]);
     MoveRange(params.buffer, locs, params.buffer);
   }
 
@@ -959,7 +867,7 @@
       continue;
     }
 
-    RangeSet locs = parse_range(tokens[1]);
+    RangeSet locs = RangeSet::Parse(tokens[1]);
     MoveRange(params.buffer, locs, stash);
   }
 
@@ -1023,7 +931,7 @@
   }
 
   // <tgt_range>
-  tgt = parse_range(params.tokens[params.cpos++]);
+  tgt = RangeSet::Parse(params.tokens[params.cpos++]);
 
   std::vector<uint8_t> tgtbuffer(tgt.size * BLOCKSIZE);
   if (ReadBlocks(tgt, tgtbuffer, params.fd) == -1) {
@@ -1135,7 +1043,7 @@
     return 0;
   }
 
-  RangeSet src = parse_range(params.tokens[params.cpos++]);
+  RangeSet src = RangeSet::Parse(params.tokens[params.cpos++]);
 
   allocate(src.size * BLOCKSIZE, params.buffer);
   if (ReadBlocks(src, params.buffer, params.fd) == -1) {
@@ -1186,7 +1094,7 @@
         return -1;
     }
 
-    RangeSet tgt = parse_range(params.tokens[params.cpos++]);
+    RangeSet tgt = RangeSet::Parse(params.tokens[params.cpos++]);
 
     LOG(INFO) << "  zeroing " << tgt.size << " blocks";
 
@@ -1228,7 +1136,7 @@
     return -1;
   }
 
-  RangeSet tgt = parse_range(params.tokens[params.cpos++]);
+  RangeSet tgt = RangeSet::Parse(params.tokens[params.cpos++]);
 
   if (params.canwrite) {
     LOG(INFO) << " writing " << tgt.size << " blocks of new data";
@@ -1351,7 +1259,7 @@
         return -1;
     }
 
-    RangeSet tgt = parse_range(params.tokens[params.cpos++]);
+    RangeSet tgt = RangeSet::Parse(params.tokens[params.cpos++]);
 
     if (params.canwrite) {
         LOG(INFO) << " erasing " << tgt.size << " blocks";
@@ -1733,7 +1641,7 @@
         return StringValue("");
     }
 
-    RangeSet rs = parse_range(ranges->data);
+    RangeSet rs = RangeSet::Parse(ranges->data);
 
     SHA_CTX ctx;
     SHA1_Init(&ctx);
@@ -1871,7 +1779,7 @@
         return StringValue("");
     }
 
-    RangeSet rs = parse_range(ranges->data);
+    RangeSet rs = RangeSet::Parse(ranges->data);
 
     uint8_t buffer[BLOCKSIZE];
 
diff --git a/updater/include/updater/rangeset.h b/updater/include/updater/rangeset.h
new file mode 100644
index 0000000..afaa82d
--- /dev/null
+++ b/updater/include/updater/rangeset.h
@@ -0,0 +1,95 @@
+/*
+ * 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 <vector>
+
+#include <android-base/logging.h>
+#include <android-base/parseint.h>
+#include <android-base/strings.h>
+
+struct RangeSet {
+  size_t count;             // Limit is INT_MAX.
+  size_t size;              // The number of blocks in the RangeSet.
+  std::vector<size_t> pos;  // Actual limit is INT_MAX.
+
+  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<size_t> pairs(num);
+    size_t size = 0;
+    for (size_t i = 0; i < num; i += 2) {
+      CHECK(android::base::ParseUint(pieces[i + 1], &pairs[i], static_cast<size_t>(INT_MAX)));
+      CHECK(android::base::ParseUint(pieces[i + 2], &pairs[i + 1], static_cast<size_t>(INT_MAX)));
+      CHECK_LT(pairs[i], pairs[i + 1])
+          << "Empty or negative range: " << pairs[i] << ", " << pairs[i + 1];
+
+      size_t sz = pairs[i + 1] - pairs[i];
+      CHECK_LE(size, SIZE_MAX - sz) << "RangeSet size overflow";
+      size += sz;
+    }
+
+    return RangeSet{ num / 2, size, std::move(pairs) };
+  }
+
+  // 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, size) << "Index " << idx << " is greater than RangeSet size " << size;
+    for (size_t i = 0; i < pos.size(); i += 2) {
+      if (idx < pos[i + 1] - pos[i]) {
+        return pos[i] + idx;
+      }
+      idx -= (pos[i + 1] - pos[i]);
+    }
+    CHECK(false);
+    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 (size_t i = 0; i < count; ++i) {
+      size_t start = pos[i * 2];
+      size_t end = pos[i * 2 + 1];
+      for (size_t j = 0; j < other.count; ++j) {
+        size_t other_start = other.pos[j * 2];
+        size_t other_end = other.pos[j * 2 + 1];
+        // [start, end) vs [other_start, other_end)
+        if (!(other_start >= end || start >= other_end)) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  bool operator==(const RangeSet& other) const {
+    return (count == other.count && size == other.size && pos == other.pos);
+  }
+};