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
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