BitSet

This module implements an array of bits, that grows as needed. It can be used from both JavaScript:

var bs = new BitSet();

for(var n = 0; n < 12; n++) {
  bs.set(n);
}

console.dir(bs);

as well as CoffeeScript:

bs = new BitSet

bs.set 1
bs.clear 1

console.log bs.toString()

Usage

BitSets are very useful for realtime metrics. If you want to count the number of active users (CoffeeScript):

# Somewhere in application code
todaysUserCount = new Bitset
    
# The User class
class User
  @login: (userName, password) ->
    todaysUserCount.set @userId
    
# In reporting code
todaysUserCount.cardinality()

Documentation

• BitSet#set(pos) - sets the bit on position pos to true
• BitSet#get(pos) - returns whether the bit on position pos is set
• BitSet#clear(pos) - clears the bit on position pos
• BitSet#length - returns the logical length of the bitset
• BitSet#wordLength - returns the word-length of the bitset
• BitSet#cardinality - returns how many bits are set to true in the bitset
• BitSet#toString - returns a string representation of the bitset
• BitSet#toBinaryString - returns a binary string representation of the bitset
• BitSet#or(bitset) - OR's this bitset with the argument bitset
• BitSet#and(bitset) - AND's this bitset with the argument bitset
• BitSet#andNot(bitset) - ANDNOT's this bitset with the argument bitset
• BitSet#xor(bitset) - XOR's this bitset with the argument bitset

For details see src/bitset.coffee

Installation

npm install bitset

Performance

It performs pretty well, you can try the performance.js in the support folder. This is the output with 100.000.000 bits:

set 100000000 bits: 3173ms
cardinality 100000000
cardinality: 949ms

Tests

Testing is done via the excellent mocha (cake test)

License

bitset is licensed under MIT license.

Copyright (C) 2012-2014 Tom de Grunt <[email protected]>

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.