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/*
 * Copyright 2017 The gRPC Authors
 *
 * 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.
 */

package org.apache.ratis.thirdparty.io.grpc;

import java.util.Arrays;

/**
 * A persistent (copy-on-write) hash tree/trie. Collisions are handled
 * linearly. Delete is not supported, but replacement is. The implementation
 * favors simplicity and low memory allocation during insertion. Although the
 * asymptotics are good, it is optimized for small sizes like less than 20;
 * "unbelievably large" would be 100.
 *
 * 

Inspired by popcnt-based compression seen in Ideal Hash Trees, Phil * Bagwell (2000). The rest of the implementation is ignorant of/ignores the * paper. */ final class PersistentHashArrayMappedTrie { private PersistentHashArrayMappedTrie() {} /** * Returns the value with the specified key, or {@code null} if it does not exist. */ static V get(Node root, K key) { if (root == null) { return null; } return root.get(key, key.hashCode(), 0); } /** * Returns a new trie where the key is set to the specified value. */ static Node put(Node root, K key, V value) { if (root == null) { return new Leaf<>(key, value); } return root.put(key, value, key.hashCode(), 0); } // Not actually annotated to avoid depending on guava // @VisibleForTesting static final class Leaf implements Node { private final K key; private final V value; public Leaf(K key, V value) { this.key = key; this.value = value; } @Override public int size() { return 1; } @Override public V get(K key, int hash, int bitsConsumed) { if (this.key == key) { return value; } else { return null; } } @Override public Node put(K key, V value, int hash, int bitsConsumed) { int thisHash = this.key.hashCode(); if (thisHash != hash) { // Insert return CompressedIndex.combine( new Leaf<>(key, value), hash, this, thisHash, bitsConsumed); } else if (this.key == key) { // Replace return new Leaf<>(key, value); } else { // Hash collision return new CollisionLeaf<>(this.key, this.value, key, value); } } @Override public String toString() { return String.format("Leaf(key=%s value=%s)", key, value); } } // Not actually annotated to avoid depending on guava // @VisibleForTesting static final class CollisionLeaf implements Node { // All keys must have same hash, but not have the same reference private final K[] keys; private final V[] values; // Not actually annotated to avoid depending on guava // @VisibleForTesting @SuppressWarnings("unchecked") CollisionLeaf(K key1, V value1, K key2, V value2) { this((K[]) new Object[] {key1, key2}, (V[]) new Object[] {value1, value2}); assert key1 != key2; assert key1.hashCode() == key2.hashCode(); } private CollisionLeaf(K[] keys, V[] values) { this.keys = keys; this.values = values; } @Override public int size() { return values.length; } @Override public V get(K key, int hash, int bitsConsumed) { for (int i = 0; i < keys.length; i++) { if (keys[i] == key) { return values[i]; } } return null; } @Override public Node put(K key, V value, int hash, int bitsConsumed) { int thisHash = keys[0].hashCode(); int keyIndex; if (thisHash != hash) { // Insert return CompressedIndex.combine( new Leaf<>(key, value), hash, this, thisHash, bitsConsumed); } else if ((keyIndex = indexOfKey(key)) != -1) { // Replace K[] newKeys = Arrays.copyOf(keys, keys.length); V[] newValues = Arrays.copyOf(values, keys.length); newKeys[keyIndex] = key; newValues[keyIndex] = value; return new CollisionLeaf<>(newKeys, newValues); } else { // Yet another hash collision K[] newKeys = Arrays.copyOf(keys, keys.length + 1); V[] newValues = Arrays.copyOf(values, keys.length + 1); newKeys[keys.length] = key; newValues[keys.length] = value; return new CollisionLeaf<>(newKeys, newValues); } } // -1 if not found private int indexOfKey(K key) { for (int i = 0; i < keys.length; i++) { if (keys[i] == key) { return i; } } return -1; } @Override public String toString() { StringBuilder valuesSb = new StringBuilder(); valuesSb.append("CollisionLeaf("); for (int i = 0; i < values.length; i++) { valuesSb.append("(key=").append(keys[i]).append(" value=").append(values[i]).append(") "); } return valuesSb.append(")").toString(); } } // Not actually annotated to avoid depending on guava // @VisibleForTesting static final class CompressedIndex implements Node { private static final int BITS = 5; private static final int BITS_MASK = 0x1F; final int bitmap; final Node[] values; private final int size; private CompressedIndex(int bitmap, Node[] values, int size) { this.bitmap = bitmap; this.values = values; this.size = size; } @Override public int size() { return size; } @Override public V get(K key, int hash, int bitsConsumed) { int indexBit = indexBit(hash, bitsConsumed); if ((bitmap & indexBit) == 0) { return null; } int compressedIndex = compressedIndex(indexBit); return values[compressedIndex].get(key, hash, bitsConsumed + BITS); } @Override public Node put(K key, V value, int hash, int bitsConsumed) { int indexBit = indexBit(hash, bitsConsumed); int compressedIndex = compressedIndex(indexBit); if ((bitmap & indexBit) == 0) { // Insert int newBitmap = bitmap | indexBit; @SuppressWarnings("unchecked") Node[] newValues = (Node[]) new Node[values.length + 1]; System.arraycopy(values, 0, newValues, 0, compressedIndex); newValues[compressedIndex] = new Leaf<>(key, value); System.arraycopy( values, compressedIndex, newValues, compressedIndex + 1, values.length - compressedIndex); return new CompressedIndex<>(newBitmap, newValues, size() + 1); } else { // Replace Node[] newValues = Arrays.copyOf(values, values.length); newValues[compressedIndex] = values[compressedIndex].put(key, value, hash, bitsConsumed + BITS); int newSize = size(); newSize += newValues[compressedIndex].size(); newSize -= values[compressedIndex].size(); return new CompressedIndex<>(bitmap, newValues, newSize); } } static Node combine( Node node1, int hash1, Node node2, int hash2, int bitsConsumed) { assert hash1 != hash2; int indexBit1 = indexBit(hash1, bitsConsumed); int indexBit2 = indexBit(hash2, bitsConsumed); if (indexBit1 == indexBit2) { Node node = combine(node1, hash1, node2, hash2, bitsConsumed + BITS); @SuppressWarnings("unchecked") Node[] values = (Node[]) new Node[] {node}; return new CompressedIndex<>(indexBit1, values, node.size()); } else { // Make node1 the smallest if (uncompressedIndex(hash1, bitsConsumed) > uncompressedIndex(hash2, bitsConsumed)) { Node nodeCopy = node1; node1 = node2; node2 = nodeCopy; } @SuppressWarnings("unchecked") Node[] values = (Node[]) new Node[] {node1, node2}; return new CompressedIndex<>(indexBit1 | indexBit2, values, node1.size() + node2.size()); } } @Override public String toString() { StringBuilder valuesSb = new StringBuilder(); valuesSb.append("CompressedIndex(") .append(String.format("bitmap=%s ", Integer.toBinaryString(bitmap))); for (Node value : values) { valuesSb.append(value).append(" "); } return valuesSb.append(")").toString(); } private int compressedIndex(int indexBit) { return Integer.bitCount(bitmap & (indexBit - 1)); } private static int uncompressedIndex(int hash, int bitsConsumed) { return (hash >>> bitsConsumed) & BITS_MASK; } private static int indexBit(int hash, int bitsConsumed) { int uncompressedIndex = uncompressedIndex(hash, bitsConsumed); return 1 << uncompressedIndex; } } interface Node { V get(K key, int hash, int bitsConsumed); Node put(K key, V value, int hash, int bitsConsumed); int size(); } }





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