bitset

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)