bitset
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A performance optimized infinite bit vector library
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[](https://npmjs.org/package/bitset "View this project on npm")
[](http://opensource.org/licenses/MIT)
BitSet.js is an infinite [Bit-Array](http://en.wikipedia.org/wiki/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.
```javascript
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
```
```javascript
let bs = new BitSet;
bs
.flip(0, 62)
.flip(29, 35);
let str = bs.toString();
if (str === "111111111111111111111111111000000011111111111111111111111111111") {
console.log("YES!");
}
```
```javascript
let bs = new BitSet;
bs.setRange(10, 18, 1); // Set a 1 between 10 and 18, inclusive
```
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:
```javascript
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));
```
```
npm install bitset
```
```html
<script src="bitset.js"></script>
<script>
console.log(BitSet("111"));
</script>
```
```html
<script src="require.js"></script>
<script>
requirejs(['bitset.js'],
function(BitSet) {
console.log(BitSet("1111"));
});
</script>
```
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")`
- Array
- The values of the array are the indices to be set to 1 : `new BitSet([1,12,9])`
- [Uint8Array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
- A binary representation in 8 bit form
- Number
- A binary value
- BitSet
- A BitSet object, which get copied over
The data type Mixed can be either a BitSet object, a String or an integer representing a native bitset with 31 bits.
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
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
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
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
Immutable; Calculates the bitwise complement
Immutable; Calculates the bitwise intersection of two bitsets
Immutable; Calculates the bitwise union of two bitsets
Immutable; Calculates the bitwise xor between two bitsets
Immutable; Calculates the bitwise difference of two bitsets (this is not the nand operation!)
### BitSet clone()
Immutable; Clones the actual object
Returns an array with all indexes set in the bitset
Returns a string representation with respect to the base
Calculates the number of bits set
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.
```js
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!
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.
After cloning the Git repository run:
```
npm install
npm run build
```
Testing the source against the shipped test suite is as easy as
```
npm run test
```
Copyright (c) 2024, [Robert Eisele](https://raw.org/)
Licensed under the MIT license.