Add a basic hashtable data structure, with tests!

The basic hashtable is intended to be used to support a variety
of different datastructures such as map, set, multimap,
multiset, linkedmap, generationcache, etc.

Consequently its interface is fairly primitive.

The basic hashtable supports copy-on-write style functionality
using SharedBuffer.

The change introduces a simple generic function in TypeHelpers for
specifying hash functions.  The idea is to add template
specializations of hash_type<T> next to the relevant data structures
such as String8, String16, sp<T>, etc.

Change-Id: I2c479229e9d4527b4fbfe3b8b04776a2fd32c973

5 files changed, 965 insertions, 1 deletions

diff --git a/libs/utils/Android.mk b/libs/utils/Android.mk
index d168d19..544ab74 100644
--- a/libs/utils/Android.mk
+++ b/libs/utils/Android.mk
@@ -21,6 +21,7 @@ commonSources:= \
 	Asset.cpp \
 	AssetDir.cpp \
 	AssetManager.cpp \
+	BasicHashtable.cpp \
 	BlobCache.cpp \
 	BufferedTextOutput.cpp \
 	CallStack.cpp \
diff --git a/libs/utils/BasicHashtable.cpp b/libs/utils/BasicHashtable.cpp
new file mode 100644
index 0000000..fb8ec9f
--- /dev/null
+++ b/libs/utils/BasicHashtable.cpp
@@ -0,0 +1,338 @@
+/*
+ * Copyright (C) 2011 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.
+ */
+
+#define LOG_TAG "BasicHashtable"
+
+#include <math.h>
+
+#include <utils/Log.h>
+#include <utils/BasicHashtable.h>
+#include <utils/misc.h>
+
+namespace android {
+
+BasicHashtableImpl::BasicHashtableImpl(size_t entrySize, bool hasTrivialDestructor,
+        size_t minimumInitialCapacity, float loadFactor) :
+        mBucketSize(entrySize + sizeof(Bucket)), mHasTrivialDestructor(hasTrivialDestructor),
+        mLoadFactor(loadFactor), mSize(0),
+        mFilledBuckets(0), mBuckets(NULL) {
+    determineCapacity(minimumInitialCapacity, mLoadFactor, &mBucketCount, &mCapacity);
+}
+
+BasicHashtableImpl::BasicHashtableImpl(const BasicHashtableImpl& other) :
+        mBucketSize(other.mBucketSize), mHasTrivialDestructor(other.mHasTrivialDestructor),
+        mCapacity(other.mCapacity), mLoadFactor(other.mLoadFactor),
+        mSize(other.mSize), mFilledBuckets(other.mFilledBuckets),
+        mBucketCount(other.mBucketCount), mBuckets(other.mBuckets) {
+    if (mBuckets) {
+        SharedBuffer::bufferFromData(mBuckets)->acquire();
+    }
+}
+
+void BasicHashtableImpl::dispose() {
+    if (mBuckets) {
+        releaseBuckets(mBuckets, mBucketCount);
+    }
+}
+
+void BasicHashtableImpl::clone() {
+    if (mBuckets) {
+        void* newBuckets = allocateBuckets(mBucketCount);
+        copyBuckets(mBuckets, newBuckets, mBucketCount);
+        releaseBuckets(mBuckets, mBucketCount);
+        mBuckets = newBuckets;
+    }
+}
+
+void BasicHashtableImpl::setTo(const BasicHashtableImpl& other) {
+    if (mBuckets) {
+        releaseBuckets(mBuckets, mBucketCount);
+    }
+
+    mCapacity = other.mCapacity;
+    mLoadFactor = other.mLoadFactor;
+    mSize = other.mSize;
+    mFilledBuckets = other.mFilledBuckets;
+    mBucketCount = other.mBucketCount;
+    mBuckets = other.mBuckets;
+
+    if (mBuckets) {
+        SharedBuffer::bufferFromData(mBuckets)->acquire();
+    }
+}
+
+void BasicHashtableImpl::clear() {
+    if (mBuckets) {
+        if (mFilledBuckets) {
+            SharedBuffer* sb = SharedBuffer::bufferFromData(mBuckets);
+            if (sb->onlyOwner()) {
+                destroyBuckets(mBuckets, mBucketCount);
+                for (size_t i = 0; i < mSize; i++) {
+                    Bucket& bucket = bucketAt(mBuckets, i);
+                    bucket.cookie = 0;
+                }
+            } else {
+                releaseBuckets(mBuckets, mBucketCount);
+                mBuckets = NULL;
+            }
+            mFilledBuckets = 0;
+        }
+        mSize = 0;
+    }
+}
+
+ssize_t BasicHashtableImpl::next(ssize_t index) const {
+    if (mSize) {
+        while (size_t(++index) < mBucketCount) {
+            const Bucket& bucket = bucketAt(mBuckets, index);
+            if (bucket.cookie & Bucket::PRESENT) {
+                return index;
+            }
+        }
+    }
+    return -1;
+}
+
+ssize_t BasicHashtableImpl::find(ssize_t index, hash_t hash,
+        const void* __restrict__ key) const {
+    if (!mSize) {
+        return -1;
+    }
+
+    hash = trimHash(hash);
+    if (index < 0) {
+        index = chainStart(hash, mBucketCount);
+
+        const Bucket& bucket = bucketAt(mBuckets, size_t(index));
+        if (bucket.cookie & Bucket::PRESENT) {
+            if (compareBucketKey(bucket, key)) {
+                return index;
+            }
+        } else {
+            if (!(bucket.cookie & Bucket::COLLISION)) {
+                return -1;
+            }
+        }
+    }
+
+    size_t inc = chainIncrement(hash, mBucketCount);
+    for (;;) {
+        index = chainSeek(index, inc, mBucketCount);
+
+        const Bucket& bucket = bucketAt(mBuckets, size_t(index));
+        if (bucket.cookie & Bucket::PRESENT) {
+            if ((bucket.cookie & Bucket::HASH_MASK) == hash
+                    && compareBucketKey(bucket, key)) {
+                return index;
+            }
+        }
+        if (!(bucket.cookie & Bucket::COLLISION)) {
+            return -1;
+        }
+    }
+}
+
+size_t BasicHashtableImpl::add(hash_t hash, const void* entry) {
+    if (!mBuckets) {
+        mBuckets = allocateBuckets(mBucketCount);
+    } else {
+        edit();
+    }
+
+    hash = trimHash(hash);
+    for (;;) {
+        size_t index = chainStart(hash, mBucketCount);
+        Bucket* bucket = &bucketAt(mBuckets, size_t(index));
+        if (bucket->cookie & Bucket::PRESENT) {
+            size_t inc = chainIncrement(hash, mBucketCount);
+            do {
+                bucket->cookie |= Bucket::COLLISION;
+                index = chainSeek(index, inc, mBucketCount);
+                bucket = &bucketAt(mBuckets, size_t(index));
+            } while (bucket->cookie & Bucket::PRESENT);
+        }
+
+        uint32_t collision = bucket->cookie & Bucket::COLLISION;
+        if (!collision) {
+            if (mFilledBuckets >= mCapacity) {
+                rehash(mCapacity * 2, mLoadFactor);
+                continue;
+            }
+            mFilledBuckets += 1;
+        }
+
+        bucket->cookie = collision | Bucket::PRESENT | hash;
+        mSize += 1;
+        initializeBucketEntry(*bucket, entry);
+        return index;
+    }
+}
+
+void BasicHashtableImpl::removeAt(size_t index) {
+    edit();
+
+    Bucket& bucket = bucketAt(mBuckets, index);
+    bucket.cookie &= ~Bucket::PRESENT;
+    if (!(bucket.cookie & Bucket::COLLISION)) {
+        mFilledBuckets -= 1;
+    }
+    mSize -= 1;
+    if (!mHasTrivialDestructor) {
+        destroyBucketEntry(bucket);
+    }
+}
+
+void BasicHashtableImpl::rehash(size_t minimumCapacity, float loadFactor) {
+    if (minimumCapacity < mSize) {
+        minimumCapacity = mSize;
+    }
+    size_t newBucketCount, newCapacity;
+    determineCapacity(minimumCapacity, loadFactor, &newBucketCount, &newCapacity);
+
+    if (newBucketCount != mBucketCount || newCapacity != mCapacity) {
+        if (mBuckets) {
+            void* newBuckets;
+            if (mSize) {
+                newBuckets = allocateBuckets(newBucketCount);
+                for (size_t i = 0; i < mBucketCount; i++) {
+                    const Bucket& fromBucket = bucketAt(mBuckets, i);
+                    if (fromBucket.cookie & Bucket::PRESENT) {
+                        hash_t hash = fromBucket.cookie & Bucket::HASH_MASK;
+                        size_t index = chainStart(hash, newBucketCount);
+                        Bucket* toBucket = &bucketAt(newBuckets, size_t(index));
+                        if (toBucket->cookie & Bucket::PRESENT) {
+                            size_t inc = chainIncrement(hash, newBucketCount);
+                            do {
+                                toBucket->cookie |= Bucket::COLLISION;
+                                index = chainSeek(index, inc, newBucketCount);
+                                toBucket = &bucketAt(newBuckets, size_t(index));
+                            } while (toBucket->cookie & Bucket::PRESENT);
+                        }
+                        toBucket->cookie = Bucket::PRESENT | hash;
+                        initializeBucketEntry(*toBucket, fromBucket.entry);
+                    }
+                }
+            } else {
+                newBuckets = NULL;
+            }
+            releaseBuckets(mBuckets, mBucketCount);
+            mBuckets = newBuckets;
+            mFilledBuckets = mSize;
+        }
+        mBucketCount = newBucketCount;
+        mCapacity = newCapacity;
+    }
+    mLoadFactor = loadFactor;
+}
+
+void* BasicHashtableImpl::allocateBuckets(size_t count) const {
+    size_t bytes = count * mBucketSize;
+    SharedBuffer* sb = SharedBuffer::alloc(bytes);
+    LOG_ALWAYS_FATAL_IF(!sb, "Could not allocate %u bytes for hashtable with %u buckets.",
+            uint32_t(bytes), uint32_t(count));
+    void* buckets = sb->data();
+    for (size_t i = 0; i < count; i++) {
+        Bucket& bucket = bucketAt(buckets, i);
+        bucket.cookie = 0;
+    }
+    return buckets;
+}
+
+void BasicHashtableImpl::releaseBuckets(void* __restrict__ buckets, size_t count) const {
+    SharedBuffer* sb = SharedBuffer::bufferFromData(buckets);
+    if (sb->release(SharedBuffer::eKeepStorage) == 1) {
+        destroyBuckets(buckets, count);
+        SharedBuffer::dealloc(sb);
+    }
+}
+
+void BasicHashtableImpl::destroyBuckets(void* __restrict__ buckets, size_t count) const {
+    if (!mHasTrivialDestructor) {
+        for (size_t i = 0; i < count; i++) {
+            Bucket& bucket = bucketAt(buckets, i);
+            if (bucket.cookie & Bucket::PRESENT) {
+                destroyBucketEntry(bucket);
+            }
+        }
+    }
+}
+
+void BasicHashtableImpl::copyBuckets(const void* __restrict__ fromBuckets,
+        void* __restrict__ toBuckets, size_t count) const {
+    for (size_t i = 0; i < count; i++) {
+        const Bucket& fromBucket = bucketAt(fromBuckets, i);
+        Bucket& toBucket = bucketAt(toBuckets, i);
+        toBucket.cookie = fromBucket.cookie;
+        if (fromBucket.cookie & Bucket::PRESENT) {
+            initializeBucketEntry(toBucket, fromBucket.entry);
+        }
+    }
+}
+
+// Table of 31-bit primes where each prime is no less than twice as large
+// as the previous one.  Generated by "primes.py".
+static size_t PRIMES[] = {
+    5,
+    11,
+    23,
+    47,
+    97,
+    197,
+    397,
+    797,
+    1597,
+    3203,
+    6421,
+    12853,
+    25717,
+    51437,
+    102877,
+    205759,
+    411527,
+    823117,
+    1646237,
+    3292489,
+    6584983,
+    13169977,
+    26339969,
+    52679969,
+    105359939,
+    210719881,
+    421439783,
+    842879579,
+    1685759167,
+    0,
+};
+
+void BasicHashtableImpl::determineCapacity(size_t minimumCapacity, float loadFactor,
+        size_t* __restrict__ outBucketCount, size_t* __restrict__ outCapacity) {
+    LOG_ALWAYS_FATAL_IF(loadFactor <= 0.0f || loadFactor > 1.0f,
+            "Invalid load factor %0.3f.  Must be in the range (0, 1].", loadFactor);
+
+    size_t count = ceilf(minimumCapacity / loadFactor) + 1;
+    size_t i = 0;
+    while (count > PRIMES[i] && i < NELEM(PRIMES)) {
+        i++;
+    }
+    count = PRIMES[i];
+    LOG_ALWAYS_FATAL_IF(!count, "Could not determine required number of buckets for "
+            "hashtable with minimum capacity %u and load factor %0.3f.",
+            uint32_t(minimumCapacity), loadFactor);
+    *outBucketCount = count;
+    *outCapacity = ceilf((count - 1) * loadFactor);
+}
+
+}; // namespace android
diff --git a/libs/utils/primes.py b/libs/utils/primes.py
new file mode 100755
index 0000000..e161dd8
--- /dev/null
+++ b/libs/utils/primes.py
@@ -0,0 +1,47 @@
+#!/usr/bin/env python2.6
+#
+# Copyright (C) 2011 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.
+#
+
+#
+# Generates a table of prime numbers for use in BasicHashtable.cpp.
+#
+# Each prime is chosen such that it is a little more than twice as large as
+# the previous prime in the table.  This makes it easier to choose a new
+# hashtable size when the underlying array is grown by as nominal factor
+# of two each time.
+#
+
+def is_odd_prime(n):
+  limit = (n - 1) / 2
+  d = 3
+  while d <= limit:
+    if n % d == 0:
+      return False
+    d += 2
+  return True
+
+print "static size_t PRIMES[] = {"
+
+n = 5
+max = 2**31 - 1
+while n < max:
+  print "    %d," % (n)
+  n = n * 2 + 1
+  while not is_odd_prime(n):
+    n += 2
+
+print "    0,"
+print "};"
diff --git a/libs/utils/tests/Android.mk b/libs/utils/tests/Android.mk
index b97f52f..58230f4 100644
--- a/libs/utils/tests/Android.mk
+++ b/libs/utils/tests/Android.mk
@@ -4,9 +4,10 @@ include $(CLEAR_VARS)
 
 # Build the unit tests.
 test_src_files := \
+	BasicHashtable_test.cpp \
 	BlobCache_test.cpp \
-	ObbFile_test.cpp \
 	Looper_test.cpp \
+	ObbFile_test.cpp \
 	String8_test.cpp \
 	Unicode_test.cpp \
 	ZipFileRO_test.cpp \
diff --git a/libs/utils/tests/BasicHashtable_test.cpp b/libs/utils/tests/BasicHashtable_test.cpp
new file mode 100644
index 0000000..764082d
--- /dev/null
+++ b/libs/utils/tests/BasicHashtable_test.cpp
@@ -0,0 +1,577 @@
+/*
+ * Copyright (C) 2011 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.
+ */
+
+#define LOG_TAG "BasicHashtable_test"
+
+#include <utils/BasicHashtable.h>
+#include <cutils/log.h>
+#include <gtest/gtest.h>
+#include <unistd.h>
+
+namespace android {
+
+typedef int SimpleKey;
+typedef int SimpleValue;
+typedef key_value_pair_t<SimpleKey, SimpleValue> SimpleEntry;
+typedef BasicHashtable<SimpleKey, SimpleEntry> SimpleHashtable;
+
+struct ComplexKey {
+    int k;
+
+    explicit ComplexKey(int k) : k(k) {
+        instanceCount += 1;
+    }
+
+    ComplexKey(const ComplexKey& other) : k(other.k) {
+        instanceCount += 1;
+    }
+
+    ~ComplexKey() {
+        instanceCount -= 1;
+    }
+
+    bool operator ==(const ComplexKey& other) const {
+        return k == other.k;
+    }
+
+    bool operator !=(const ComplexKey& other) const {
+        return k != other.k;
+    }
+
+    static ssize_t instanceCount;
+};
+
+ssize_t ComplexKey::instanceCount = 0;
+
+template<> inline hash_t hash_type(const ComplexKey& value) {
+    return hash_type(value.k);
+}
+
+struct ComplexValue {
+    int v;
+
+    explicit ComplexValue(int v) : v(v) {
+        instanceCount += 1;
+    }
+
+    ComplexValue(const ComplexValue& other) : v(other.v) {
+        instanceCount += 1;
+    }
+
+    ~ComplexValue() {
+        instanceCount -= 1;
+    }
+
+    static ssize_t instanceCount;
+};
+
+ssize_t ComplexValue::instanceCount = 0;
+
+typedef key_value_pair_t<ComplexKey, ComplexValue> ComplexEntry;
+typedef BasicHashtable<ComplexKey, ComplexEntry> ComplexHashtable;
+
+class BasicHashtableTest : public testing::Test {
+protected:
+    virtual void SetUp() {
+        ComplexKey::instanceCount = 0;
+        ComplexValue::instanceCount = 0;
+    }
+
+    virtual void TearDown() {
+        ASSERT_NO_FATAL_FAILURE(assertInstanceCount(0, 0));
+    }
+
+    void assertInstanceCount(ssize_t keys, ssize_t values) {
+        if (keys != ComplexKey::instanceCount || values != ComplexValue::instanceCount) {
+            FAIL() << "Expected " << keys << " keys and " << values << " values "
+                    "but there were actually " << ComplexKey::instanceCount << " keys and "
+                    << ComplexValue::instanceCount << " values";
+        }
+    }
+
+public:
+    template <typename TKey, typename TEntry>
+    static void cookieAt(const BasicHashtable<TKey, TEntry>& h, size_t index,
+            bool* collision, bool* present, hash_t* hash) {
+        uint32_t cookie = h.cookieAt(index);
+        *collision = cookie & BasicHashtable<TKey, TEntry>::Bucket::COLLISION;
+        *present = cookie & BasicHashtable<TKey, TEntry>::Bucket::PRESENT;
+        *hash = cookie & BasicHashtable<TKey, TEntry>::Bucket::HASH_MASK;
+    }
+
+    template <typename TKey, typename TEntry>
+    static const void* getBuckets(const BasicHashtable<TKey, TEntry>& h) {
+        return h.mBuckets;
+    }
+};
+
+template <typename TKey, typename TValue>
+static size_t add(BasicHashtable<TKey, key_value_pair_t<TKey, TValue> >& h,
+        const TKey& key, const TValue& value) {
+    return h.add(hash_type(key), key_value_pair_t<TKey, TValue>(key, value));
+}
+
+template <typename TKey, typename TValue>
+static ssize_t find(BasicHashtable<TKey, key_value_pair_t<TKey, TValue> >& h,
+        ssize_t index, const TKey& key) {
+    return h.find(index, hash_type(key), key);
+}
+
+template <typename TKey, typename TValue>
+static bool remove(BasicHashtable<TKey, key_value_pair_t<TKey, TValue> >& h,
+        const TKey& key) {
+    ssize_t index = find(h, -1, key);
+    if (index >= 0) {
+        h.removeAt(index);
+        return true;
+    }
+    return false;
+}
+
+template <typename TEntry>
+static void getKeyValue(const TEntry& entry, int* key, int* value);
+
+template <> void getKeyValue(const SimpleEntry& entry, int* key, int* value) {
+    *key = entry.key;
+    *value = entry.value;
+}
+
+template <> void getKeyValue(const ComplexEntry& entry, int* key, int* value) {
+    *key = entry.key.k;
+    *value = entry.value.v;
+}
+
+template <typename TKey, typename TValue>
+static void dump(BasicHashtable<TKey, key_value_pair_t<TKey, TValue> >& h) {
+    LOGD("hashtable %p, size=%u, capacity=%u, bucketCount=%u",
+            &h, h.size(), h.capacity(), h.bucketCount());
+    for (size_t i = 0; i < h.bucketCount(); i++) {
+        bool collision, present;
+        hash_t hash;
+        BasicHashtableTest::cookieAt(h, i, &collision, &present, &hash);
+        if (present) {
+            int key, value;
+            getKeyValue(h.entryAt(i), &key, &value);
+            LOGD("  [%3u] = collision=%d, present=%d, hash=0x%08x, key=%3d, value=%3d, "
+                    "hash_type(key)=0x%08x",
+                    i, collision, present, hash, key, value, hash_type(key));
+        } else {
+            LOGD("  [%3u] = collision=%d, present=%d",
+                    i, collision, present);
+        }
+    }
+}
+
+TEST_F(BasicHashtableTest, DefaultConstructor_WithDefaultProperties) {
+    SimpleHashtable h;
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(3U, h.capacity());
+    EXPECT_EQ(5U, h.bucketCount());
+    EXPECT_EQ(0.75f, h.loadFactor());
+}
+
+TEST_F(BasicHashtableTest, Constructor_WithNonUnityLoadFactor) {
+    SimpleHashtable h(52, 0.8f);
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(77U, h.capacity());
+    EXPECT_EQ(97U, h.bucketCount());
+    EXPECT_EQ(0.8f, h.loadFactor());
+}
+
+TEST_F(BasicHashtableTest, Constructor_WithUnityLoadFactorAndExactCapacity) {
+    SimpleHashtable h(46, 1.0f);
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(46U, h.capacity()); // must be one less than bucketCount because loadFactor == 1.0f
+    EXPECT_EQ(47U, h.bucketCount());
+    EXPECT_EQ(1.0f, h.loadFactor());
+}
+
+TEST_F(BasicHashtableTest, Constructor_WithUnityLoadFactorAndInexactCapacity) {
+    SimpleHashtable h(42, 1.0f);
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(46U, h.capacity()); // must be one less than bucketCount because loadFactor == 1.0f
+    EXPECT_EQ(47U, h.bucketCount());
+    EXPECT_EQ(1.0f, h.loadFactor());
+}
+
+TEST_F(BasicHashtableTest, FindAddFindRemoveFind_OneEntry) {
+    SimpleHashtable h;
+    ssize_t index = find(h, -1, 8);
+    ASSERT_EQ(-1, index);
+
+    index = add(h, 8, 1);
+    ASSERT_EQ(1U, h.size());
+
+    ASSERT_EQ(index, find(h, -1, 8));
+    ASSERT_EQ(8, h.entryAt(index).key);
+    ASSERT_EQ(1, h.entryAt(index).value);
+
+    index = find(h, index, 8);
+    ASSERT_EQ(-1, index);
+
+    ASSERT_TRUE(remove(h, 8));
+    ASSERT_EQ(0U, h.size());
+
+    index = find(h, -1, 8);
+    ASSERT_EQ(-1, index);
+}
+
+TEST_F(BasicHashtableTest, FindAddFindRemoveFind_MultipleEntryWithUniqueKey) {
+    const size_t N = 11;
+
+    SimpleHashtable h;
+    for (size_t i = 0; i < N; i++) {
+        ssize_t index = find(h, -1, int(i));
+        ASSERT_EQ(-1, index);
+
+        index = add(h, int(i), int(i * 10));
+        ASSERT_EQ(i + 1, h.size());
+
+        ASSERT_EQ(index, find(h, -1, int(i)));
+        ASSERT_EQ(int(i), h.entryAt(index).key);
+        ASSERT_EQ(int(i * 10), h.entryAt(index).value);
+
+        index = find(h, index, int(i));
+        ASSERT_EQ(-1, index);
+    }
+
+    for (size_t i = N; --i > 0; ) {
+        ASSERT_TRUE(remove(h, int(i))) << "i = " << i;
+        ASSERT_EQ(i, h.size());
+
+        ssize_t index = find(h, -1, int(i));
+        ASSERT_EQ(-1, index);
+    }
+}
+
+TEST_F(BasicHashtableTest, FindAddFindRemoveFind_MultipleEntryWithDuplicateKey) {
+    const size_t N = 11;
+    const int K = 1;
+
+    SimpleHashtable h;
+    for (size_t i = 0; i < N; i++) {
+        ssize_t index = find(h, -1, K);
+        if (i == 0) {
+            ASSERT_EQ(-1, index);
+        } else {
+            ASSERT_NE(-1, index);
+        }
+
+        add(h, K, int(i));
+        ASSERT_EQ(i + 1, h.size());
+
+        index = -1;
+        int values = 0;
+        for (size_t j = 0; j <= i; j++) {
+            index = find(h, index, K);
+            ASSERT_GE(index, 0);
+            ASSERT_EQ(K, h.entryAt(index).key);
+            values |= 1 << h.entryAt(index).value;
+        }
+        ASSERT_EQ(values, (1 << (i + 1)) - 1);
+
+        index = find(h, index, K);
+        ASSERT_EQ(-1, index);
+    }
+
+    for (size_t i = N; --i > 0; ) {
+        ASSERT_TRUE(remove(h, K)) << "i = " << i;
+        ASSERT_EQ(i, h.size());
+
+        ssize_t index = -1;
+        for (size_t j = 0; j < i; j++) {
+            index = find(h, index, K);
+            ASSERT_GE(index, 0);
+            ASSERT_EQ(K, h.entryAt(index).key);
+        }
+
+        index = find(h, index, K);
+        ASSERT_EQ(-1, index);
+    }
+}
+
+TEST_F(BasicHashtableTest, Clear_WhenAlreadyEmpty_DoesNothing) {
+    SimpleHashtable h;
+    h.clear();
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(3U, h.capacity());
+    EXPECT_EQ(5U, h.bucketCount());
+    EXPECT_EQ(0.75f, h.loadFactor());
+}
+
+TEST_F(BasicHashtableTest, Clear_AfterElementsAdded_RemovesThem) {
+    SimpleHashtable h;
+    add(h, 0, 0);
+    add(h, 1, 0);
+    h.clear();
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(3U, h.capacity());
+    EXPECT_EQ(5U, h.bucketCount());
+    EXPECT_EQ(0.75f, h.loadFactor());
+}
+
+TEST_F(BasicHashtableTest, Clear_AfterElementsAdded_DestroysThem) {
+    ComplexHashtable h;
+    add(h, ComplexKey(0), ComplexValue(0));
+    add(h, ComplexKey(1), ComplexValue(0));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+
+    h.clear();
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(0, 0));
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(3U, h.capacity());
+    EXPECT_EQ(5U, h.bucketCount());
+    EXPECT_EQ(0.75f, h.loadFactor());
+}
+
+TEST_F(BasicHashtableTest, Remove_AfterElementsAdded_DestroysThem) {
+    ComplexHashtable h;
+    add(h, ComplexKey(0), ComplexValue(0));
+    add(h, ComplexKey(1), ComplexValue(0));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+
+    ASSERT_TRUE(remove(h, ComplexKey(0)));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(1, 1));
+
+    ASSERT_TRUE(remove(h, ComplexKey(1)));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(0, 0));
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(3U, h.capacity());
+    EXPECT_EQ(5U, h.bucketCount());
+    EXPECT_EQ(0.75f, h.loadFactor());
+}
+
+TEST_F(BasicHashtableTest, Destructor_AfterElementsAdded_DestroysThem) {
+    {
+        ComplexHashtable h;
+        add(h, ComplexKey(0), ComplexValue(0));
+        add(h, ComplexKey(1), ComplexValue(0));
+        ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+    } // h is destroyed here
+
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(0, 0));
+}
+
+TEST_F(BasicHashtableTest, Next_WhenEmpty_ReturnsMinusOne) {
+    SimpleHashtable h;
+
+    ASSERT_EQ(-1, h.next(-1));
+}
+
+TEST_F(BasicHashtableTest, Next_WhenNonEmpty_IteratesOverAllEntries) {
+    const int N = 88;
+
+    SimpleHashtable h;
+    for (int i = 0; i < N; i++) {
+        add(h, i, i * 10);
+    }
+
+    bool set[N];
+    memset(set, 0, sizeof(bool) * N);
+    int count = 0;
+    for (ssize_t index = -1; (index = h.next(index)) != -1; ) {
+        ASSERT_GE(index, 0);
+        ASSERT_LT(size_t(index), h.bucketCount());
+
+        const SimpleEntry& entry = h.entryAt(index);
+        ASSERT_GE(entry.key, 0);
+        ASSERT_LT(entry.key, N);
+        ASSERT_EQ(false, set[entry.key]);
+        ASSERT_EQ(entry.key * 10, entry.value);
+
+        set[entry.key] = true;
+        count += 1;
+    }
+    ASSERT_EQ(N, count);
+}
+
+TEST_F(BasicHashtableTest, Add_RehashesOnDemand) {
+    SimpleHashtable h;
+    size_t initialCapacity = h.capacity();
+    size_t initialBucketCount = h.bucketCount();
+
+    for (size_t i = 0; i < initialCapacity; i++) {
+        add(h, int(i), 0);
+    }
+
+    EXPECT_EQ(initialCapacity, h.size());
+    EXPECT_EQ(initialCapacity, h.capacity());
+    EXPECT_EQ(initialBucketCount, h.bucketCount());
+
+    add(h, -1, -1);
+
+    EXPECT_EQ(initialCapacity + 1, h.size());
+    EXPECT_GT(h.capacity(), initialCapacity);
+    EXPECT_GT(h.bucketCount(), initialBucketCount);
+    EXPECT_GT(h.bucketCount(), h.capacity());
+}
+
+TEST_F(BasicHashtableTest, Rehash_WhenCapacityAndBucketCountUnchanged_DoesNothing) {
+    ComplexHashtable h;
+    add(h, ComplexKey(0), ComplexValue(0));
+    const void* oldBuckets = getBuckets(h);
+    ASSERT_NE((void*)NULL, oldBuckets);
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(1, 1));
+
+    h.rehash(h.capacity(), h.loadFactor());
+
+    ASSERT_EQ(oldBuckets, getBuckets(h));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(1, 1));
+}
+
+TEST_F(BasicHashtableTest, Rehash_WhenEmptyAndHasNoBuckets_ButDoesNotAllocateBuckets) {
+    ComplexHashtable h;
+    ASSERT_EQ((void*)NULL, getBuckets(h));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(0, 0));
+
+    h.rehash(9, 1.0f);
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(10U, h.capacity());
+    EXPECT_EQ(11U, h.bucketCount());
+    EXPECT_EQ(1.0f, h.loadFactor());
+    EXPECT_EQ((void*)NULL, getBuckets(h));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(0, 0));
+}
+
+TEST_F(BasicHashtableTest, Rehash_WhenEmptyAndHasBuckets_ReleasesBucketsAndSetsCapacity) {
+    ComplexHashtable h(10);
+    add(h, ComplexKey(0), ComplexValue(0));
+    ASSERT_TRUE(remove(h, ComplexKey(0)));
+    ASSERT_NE((void*)NULL, getBuckets(h));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(0, 0));
+
+    h.rehash(0, 0.75f);
+
+    EXPECT_EQ(0U, h.size());
+    EXPECT_EQ(3U, h.capacity());
+    EXPECT_EQ(5U, h.bucketCount());
+    EXPECT_EQ(0.75f, h.loadFactor());
+    EXPECT_EQ((void*)NULL, getBuckets(h));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(0, 0));
+}
+
+TEST_F(BasicHashtableTest, Rehash_WhenLessThanCurrentCapacity_ShrinksBuckets) {
+    ComplexHashtable h(10);
+    add(h, ComplexKey(0), ComplexValue(0));
+    add(h, ComplexKey(1), ComplexValue(1));
+    const void* oldBuckets = getBuckets(h);
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+
+    h.rehash(0, 0.75f);
+
+    EXPECT_EQ(2U, h.size());
+    EXPECT_EQ(3U, h.capacity());
+    EXPECT_EQ(5U, h.bucketCount());
+    EXPECT_EQ(0.75f, h.loadFactor());
+    EXPECT_NE(oldBuckets, getBuckets(h));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+}
+
+TEST_F(BasicHashtableTest, CopyOnWrite) {
+    ComplexHashtable h1;
+    add(h1, ComplexKey(0), ComplexValue(0));
+    add(h1, ComplexKey(1), ComplexValue(1));
+    const void* originalBuckets = getBuckets(h1);
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+    ssize_t index0 = find(h1, -1, ComplexKey(0));
+    EXPECT_GE(index0, 0);
+
+    // copy constructor acquires shared reference
+    ComplexHashtable h2(h1);
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+    ASSERT_EQ(originalBuckets, getBuckets(h2));
+    EXPECT_EQ(h1.size(), h2.size());
+    EXPECT_EQ(h1.capacity(), h2.capacity());
+    EXPECT_EQ(h1.bucketCount(), h2.bucketCount());
+    EXPECT_EQ(h1.loadFactor(), h2.loadFactor());
+    EXPECT_EQ(index0, find(h2, -1, ComplexKey(0)));
+
+    // operator= acquires shared reference
+    ComplexHashtable h3;
+    h3 = h2;
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+    ASSERT_EQ(originalBuckets, getBuckets(h3));
+    EXPECT_EQ(h1.size(), h3.size());
+    EXPECT_EQ(h1.capacity(), h3.capacity());
+    EXPECT_EQ(h1.bucketCount(), h3.bucketCount());
+    EXPECT_EQ(h1.loadFactor(), h3.loadFactor());
+    EXPECT_EQ(index0, find(h3, -1, ComplexKey(0)));
+
+    // editEntryAt copies shared contents
+    h1.editEntryAt(index0).value.v = 42;
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(4, 4));
+    ASSERT_NE(originalBuckets, getBuckets(h1));
+    EXPECT_EQ(42, h1.entryAt(index0).value.v);
+    EXPECT_EQ(0, h2.entryAt(index0).value.v);
+    EXPECT_EQ(0, h3.entryAt(index0).value.v);
+
+    // clear releases reference to shared contents
+    h2.clear();
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(4, 4));
+    EXPECT_EQ(0U, h2.size());
+    ASSERT_NE(originalBuckets, getBuckets(h2));
+
+    // operator= acquires shared reference, destroys unshared contents
+    h1 = h3;
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+    ASSERT_EQ(originalBuckets, getBuckets(h1));
+    EXPECT_EQ(h3.size(), h1.size());
+    EXPECT_EQ(h3.capacity(), h1.capacity());
+    EXPECT_EQ(h3.bucketCount(), h1.bucketCount());
+    EXPECT_EQ(h3.loadFactor(), h1.loadFactor());
+    EXPECT_EQ(index0, find(h1, -1, ComplexKey(0)));
+
+    // add copies shared contents
+    add(h1, ComplexKey(2), ComplexValue(2));
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(5, 5));
+    ASSERT_NE(originalBuckets, getBuckets(h1));
+    EXPECT_EQ(3U, h1.size());
+    EXPECT_EQ(0U, h2.size());
+    EXPECT_EQ(2U, h3.size());
+
+    // remove copies shared contents
+    h1 = h3;
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+    ASSERT_EQ(originalBuckets, getBuckets(h1));
+    h1.removeAt(index0);
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(3, 3));
+    ASSERT_NE(originalBuckets, getBuckets(h1));
+    EXPECT_EQ(1U, h1.size());
+    EXPECT_EQ(0U, h2.size());
+    EXPECT_EQ(2U, h3.size());
+
+    // rehash copies shared contents
+    h1 = h3;
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(2, 2));
+    ASSERT_EQ(originalBuckets, getBuckets(h1));
+    h1.rehash(10, 1.0f);
+    ASSERT_NO_FATAL_FAILURE(assertInstanceCount(4, 4));
+    ASSERT_NE(originalBuckets, getBuckets(h1));
+    EXPECT_EQ(2U, h1.size());
+    EXPECT_EQ(0U, h2.size());
+    EXPECT_EQ(2U, h3.size());
+}
+
+} // namespace android