Press n or j to go to the next uncovered block, b, p or k for the previous block.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 | /**
* DataBlock
* @param {number} localDepth
* @param {number} dataBlockSize
* @constructor
*/
function DataBlock(localDepth, dataBlockSize) {
this.localDepth = localDepth;
this.elements = new Array(dataBlockSize);
}
/**
* The hash function.
* @param key
* @param globalDepth
* @returns {number}
*/
function hash(key, globalDepth) {
// BitMask consists of <globalDepth> 1s.
const bitMask = (2 ** globalDepth) - 1; // Sum of 2^x series: 1 + 2 + 4 ...
// only retain the rightmost <globalDepth> bits
// eslint-disable-next-line no-bitwise
return key & bitMask;
}
export default class ExtendibleHashing {
/**
* ?
* @type {number}
*/
globalDepth;
/**
* The Hash Table consists of a list of DataBlocks that hold the values.
* @type {DataBlock[]}
*/
dataBlocks;
/**
* Number of elements within a DataBlock
* @type {number}
*/
dataBlockSize;
/**
* Initialize an empty hash table.
* @param {number} globalDepth
* @param {number} dataBlockSize
*/
init(globalDepth = 1, dataBlockSize = 4) {
this.globalDepth = globalDepth;
this.dataBlockSize = dataBlockSize;
this.dataBlocks = [];
// Initially, every index shall reference its own personal DataBlock, thus
// localDepth = globalDepth for all DataBlocks.
for (let address = 0; address < 2 ** this.globalDepth; address += 1) {
this.dataBlocks[address] = new DataBlock(this.globalDepth, this.dataBlockSize);
}
}
/**
* Insert a value into the hash table.
* @param value
*/
insert(value) {
let inserted = false;
while (!inserted) {
const address = hash(value, this.globalDepth);
// 1) Add value
let freeElementIndex;
for (let i = 0; i < this.dataBlockSize; i += 1) {
if (this.dataBlocks[address].elements[i] === value) {
// Value exists
inserted = true;
break;
}
if (freeElementIndex === undefined && this.dataBlocks[address].elements[i] === undefined) {
// Remember the first free slot
freeElementIndex = i;
}
// Insert value in a free slot
if (i === (this.dataBlockSize - 1) && freeElementIndex !== undefined) {
this.dataBlocks[address].elements[freeElementIndex] = value;
inserted = true;
break;
}
}
// temporary until split is moved out:
if (inserted) {
break;
}
// not inserted, overflow, split!
if (this.dataBlocks[address].localDepth < this.globalDepth) {
// if localDepth < globalDepth: split the DataBlock
// Save old DataBlock elements
const oldElements = this.dataBlocks[address].elements;
// create a new DataBlock with increased localDepth at the current address
this.dataBlocks[address] = new DataBlock(
this.dataBlocks[address].localDepth + 1,
this.dataBlockSize,
);
// Move oldElements to new DataBlock if necessary (???)
let freePosNew = 0;
// loop over old elements
for (let i = 0; i < this.dataBlockSize; i += 1) {
const newAddress = hash(oldElements[i], this.dataBlocks[address].localDepth);
if (newAddress === address) {
this.dataBlocks[address].elements[freePosNew] = oldElements[i];
freePosNew += 1;
oldElements[i] = undefined;
}
}
// expanded, try to insert in next iteration
}
if (this.dataBlocks[address].localDepth === this.globalDepth) {
// if localDepth == globalDepth: Expand Index
// Double the size of the DataBlock array and point the new fields to the
// old ones sequentially from 0 to the last field of the "old" array
const dataBlockArrayLengthOld = this.dataBlocks.length;
for (let i = dataBlockArrayLengthOld; i < 2 * dataBlockArrayLengthOld; i += 1) {
this.dataBlocks[i] = this.dataBlocks[i - dataBlockArrayLengthOld];
}
this.globalDepth += 1;
// expanded, try to insert in next iteration
}
}
if (inserted) {
// inserted
} else {
// not inserted
}
}
/**
* Search the given value in the hash table.
* @param value
*/
search(value) {
const address = hash(value, this.globalDepth);
let found = false;
for (let i = 0; i < this.dataBlocks[address].elements.length; i += 1) {
if (this.dataBlocks[address].elements[i] === value) {
found = true;
break;
}
}
if (found) {
// found
} else {
// not found
}
}
/**
* Remove the given value from the hash table.
* @param value
*/
remove(value) {
const address = hash(value, this.globalDepth);
let removed = false;
for (let i = 0; i < this.dataBlocks[address].elements.length; i += 1) {
if (this.dataBlocks[address].elements[i] === value) {
this.dataBlocks[address].elements[i] = undefined;
removed = true;
break;
}
}
if (removed) {
// removed
} else {
// not found, not removed
}
}
}
|