Awesome
BitSet.js
BitSet.js is an infinite Bit-Array (aka bit vector, bit string, bit set) implementation in JavaScript. Infinite means that if you invert a bit vector, the leading ones get remembered. As far as I can tell, BitSet.js is the only library which has this feature. It is also heavily benchmarked against other implementations and is the most performant implementation to date.
Examples
Basic usage
let bs = new BitSet;
bs.set(128, 1); // Set bit at position 128
console.log(bs.toString(16)); // Print out a hex dump with one bit set
Flipping bits
let bs = new BitSet;
bs
.flip(0, 62)
.flip(29, 35);
let str = bs.toString();
if (str === "111111111111111111111111111000000011111111111111111111111111111") {
console.log("YES!");
}
Range Set
let bs = new BitSet;
bs.setRange(10, 18, 1); // Set a 1 between 10 and 18, inclusive
User permissions
If you want to store user permissions in your database and use BitSet for the bit twiddling, you can start with the following Linux-style snippet:
let P_READ = 2; // Bit pos
let P_WRITE = 1;
let P_EXEC = 0;
let user = new BitSet;
user.set(P_READ); // Give read perms
user.set(P_WRITE); // Give write perms
let group = new BitSet(P_READ);
let world = new BitSet(P_EXEC);
console.log("0" + user.toString(8) + group.toString(8) + world.toString(8));
Installation
npm install bitset
or
bower install bitset.js
Using BitSet.js with the browser
<script src="bitset.js"></script>
<script>
console.log(BitSet("111"));
</script>
Using BitSet.js with require.js
<script src="require.js"></script>
<script>
requirejs(['bitset.js'],
function(BitSet) {
console.log(BitSet("1111"));
});
</script>
Constructor
The default BitSet
constructor accepts a single value of one the following types :
- String
- Binary strings :
new BitSet("010101")
- Binary strings with prefix :
new BitSet("0b010101")
- Hexadecimal strings with prefix
new BitSet("0xaffe")
- Binary strings :
- Array
- The values of the array are the indices to be set to 1 :
new BitSet([1,12,9])
- The values of the array are the indices to be set to 1 :
- Uint8Array
- A binary representation in 8 bit form
- Number
- A binary value
- BitSet
- A BitSet object, which get copied over
Functions
The data type Mixed can be either a BitSet object, a String or an integer representing a native bitset with 31 bits.
BitSet set(ndx[, value=1])
Mutable; Sets value 0 or 1 to index ndx
of the bitset
int get(ndx)
Gets the value at index ndx
BitSet setRange(from, to[, value=1])
Mutable; Helper function for set, to set an entire range to a given value
BitSet clear([from[, to]])
Mutable; Sets a portion of a given bitset to zero
- If no param is given, the whole bitset gets cleared
- If one param is given, the bit at this index gets cleared
- If two params are given, the range is cleared
BitSet slice([from[, to]])
Immutable; Extracts a portion of a given bitset as a new bitset
- If no param is given, the bitset is getting cloned
- If one param is given, the index is used as offset
- If two params are given, the range is returned as new BitSet
BitSet flip([from[, to]])
Mutable; Toggles a portion of a given bitset
- If no param is given, the bitset is inverted
- If one param is given, the bit at the index is toggled
- If two params are given, the bits in the given range are toggled
BitSet not()
Immutable; Calculates the bitwise complement
BitSet and(Mixed x)
Immutable; Calculates the bitwise intersection of two bitsets
BitSet or(Mixed x)
Immutable; Calculates the bitwise union of two bitsets
BitSet xor(Mixed x)
Immutable; Calculates the bitwise xor between two bitsets
BitSet andNot(Mixed x)
Immutable; Calculates the bitwise difference of two bitsets (this is not the nand operation!)
BitSet clone()
Immutable; Clones the actual object
Array toArray()
Returns an array with all indexes set in the bitset
String toString([base=2])
Returns a string representation with respect to the base
int cardinality()
Calculates the number of bits set
int msb()
Calculates the most significant bit (the left most)
int ntz()
Calculates the number of trailing zeros (zeros on the right). If all digits are zero, Infinity
is returned, since BitSet.js is an arbitrary large bit vector implementation.
int lsb()
Calculates the least significant bit (the right most)
bool isEmpty()
Checks if the bitset has all bits set to zero
bool equals()
Checks if two bitsets are the same
BitSet.fromBinaryString(str)
Alternative constructor to pass with a binary string
BitSet.fromHexString(str)
Alternative constructor to pass a hex string
BitSet.Random([n=32])
Create a random BitSet with a maximum length of n bits
Iterator Interface
A BitSet
object is iterable. The iterator gets all bits up to the most significant bit. If no bits are set, the iteration stops immediately.
let bs = BitSet.Random(55);
for (let b of bs) {
console.log(b);
}
Note: If the bitset is inverted so that all leading bits are 1, the iterator must be stopped by the user!
Coding Style
As every library I publish, BitSet.js is also built to be as small as possible after compressing it with Google Closure Compiler in advanced mode. Thus the coding style orientates a little on maxing-out the compression rate. Please make sure you keep this style if you plan to extend the library.
Build the library
Gulp is optional for minifying with Google Closure Compiler. After cloning the Git repository, do:
npm install
gulp
Run a test
Testing the source against the shipped test suite is as easy as
npm test
Copyright and licensing
Copyright (c) 2014-2023, Robert Eisele Dual licensed under the MIT or GPL Version 2 licenses.