diff --git a/libs/battery/LongArrayMultiStateCounter.cpp b/libs/battery/LongArrayMultiStateCounter.cpp
index 125cfaf..35c40ab 100644
--- a/libs/battery/LongArrayMultiStateCounter.cpp
+++ b/libs/battery/LongArrayMultiStateCounter.cpp
@@ -21,59 +21,135 @@
 namespace android {
 namespace battery {
 
+Uint64ArrayRW::Uint64ArrayRW(const Uint64Array &copy) : Uint64Array(copy.size()) {
+    if (mSize != 0 && copy.data() != nullptr) {
+        mData = new uint64_t[mSize];
+        memcpy(mData, copy.data(), mSize * sizeof(uint64_t));
+    } else {
+        mData = nullptr;
+    }
+}
+
+uint64_t *Uint64ArrayRW::dataRW() {
+    if (mData == nullptr) {
+        mData = new uint64_t[mSize];
+        memset(mData, 0, mSize * sizeof(uint64_t));
+    }
+    return mData;
+}
+
+Uint64ArrayRW &Uint64ArrayRW::operator=(const Uint64Array &t) {
+    if (t.size() != mSize) {
+        delete[] mData;
+        mSize = t.size();
+        mData = nullptr;
+    }
+    if (mSize != 0) {
+        if (t.data() != nullptr) {
+            mData = new uint64_t[mSize];
+            memcpy(mData, t.data(), mSize * sizeof(uint64_t));
+        } else {
+            mData = nullptr;
+        }
+    }
+    return *this;
+}
+
+std::ostream &operator<<(std::ostream &os, const Uint64Array &v) {
+    os << "{";
+    const uint64_t *data = v.data();
+    if (data != nullptr) {
+        bool first = true;
+        for (size_t i = 0; i < v.size(); i++) {
+            if (!first) {
+                os << ", ";
+            }
+            os << data[i];
+            first = false;
+        }
+    }
+    os << "}";
+    return os;
+}
+
+// Convenience constructor for tests
+Uint64ArrayRW::Uint64ArrayRW(std::initializer_list<uint64_t> init) : Uint64Array(init.size()) {
+    mData = new uint64_t[mSize];
+    memcpy(mData, init.begin(), mSize * sizeof(uint64_t));
+}
+
+// Used in tests only.
+bool Uint64Array::operator==(const Uint64Array &other) const {
+    if (size() != other.size()) {
+        return false;
+    }
+    const uint64_t* thisData = data();
+    const uint64_t* thatData = other.data();
+    for (size_t i = 0; i < mSize; i++) {
+        const uint64_t v1 = thisData != nullptr ? thisData[i] : 0;
+        const uint64_t v2 = thatData != nullptr ? thatData[i] : 0;
+        if (v1 != v2) {
+            return false;
+        }
+    }
+    return true;
+}
+
 template <>
-bool LongArrayMultiStateCounter::delta(const std::vector<uint64_t>& previousValue,
-                                       const std::vector<uint64_t>& newValue,
-                                       std::vector<uint64_t>* outValue) const {
+void LongArrayMultiStateCounter::add(Uint64ArrayRW *value1, const Uint64Array &value2,
+                                     const uint64_t numerator, const uint64_t denominator) const {
+    const uint64_t* data2 = value2.data();
+    if (data2 == nullptr) {
+        return;
+    }
+
+    uint64_t* data1 = value1->dataRW();
+    size_t size = value2.size();
+    if (numerator != denominator) {
+        for (size_t i = 0; i < size; i++) {
+            // The caller ensures that denominator != 0
+            data1[i] += data2[i] * numerator / denominator;
+        }
+    } else {
+        for (size_t i = 0; i < size; i++) {
+            data1[i] += data2[i];
+        }
+    }
+}
+
+template<>
+bool LongArrayMultiStateCounter::delta(const Uint64ArrayRW &previousValue,
+                                       const Uint64Array &newValue, Uint64ArrayRW *outValue) const {
     size_t size = previousValue.size();
     if (newValue.size() != size) {
-        ALOGE("Incorrect array size: %d, should be %d", (int)newValue.size(), (int)size);
+        ALOGE("Incorrect array size: %d, should be %d", (int) newValue.size(), (int) size);
+        return false;
+    }
+    if (outValue->size() != size) {
+        ALOGE("Incorrect outValue size: %d, should be %d", (int) outValue->size(), (int) size);
         return false;
     }
 
     bool is_delta_valid = true;
-    for (int i = size - 1; i >= 0; i--) {
-        if (newValue[i] >= previousValue[i]) {
-            (*outValue)[i] = newValue[i] - previousValue[i];
-        } else {
-            (*outValue)[i] = 0;
+    const uint64_t *prevData = previousValue.data();
+    const uint64_t *newData = newValue.data();
+    uint64_t *outData = outValue->dataRW();
+    for (size_t i = 0; i < size; i++) {
+        if (prevData == nullptr) {
+            if (newData == nullptr) {
+                outData[i] = 0;
+            } else {
+                outData[i] = newData[i];
+            }
+        } else if (newData == nullptr || newData[i] < prevData[i]) {
+            outData[i] = 0;
             is_delta_valid = false;
+        } else {
+            outData[i] = newData[i] - prevData[i];
         }
     }
     return is_delta_valid;
 }
 
-template <>
-void LongArrayMultiStateCounter::add(std::vector<uint64_t>* value1,
-                                     const std::vector<uint64_t>& value2, const uint64_t numerator,
-                                     const uint64_t denominator) const {
-    if (numerator != denominator) {
-        for (int i = value2.size() - 1; i >= 0; i--) {
-            // The caller ensures that denominator != 0
-            (*value1)[i] += value2[i] * numerator / denominator;
-        }
-    } else {
-        for (int i = value2.size() - 1; i >= 0; i--) {
-            (*value1)[i] += value2[i];
-        }
-    }
-}
-
-template <>
-std::string LongArrayMultiStateCounter::valueToString(const std::vector<uint64_t>& v) const {
-    std::stringstream s;
-    s << "{";
-    bool first = true;
-    for (uint64_t n : v) {
-        if (!first) {
-            s << ", ";
-        }
-        s << n;
-        first = false;
-    }
-    s << "}";
-    return s.str();
-}
-
 } // namespace battery
 } // namespace android