Bitset
A fast Bitset implementation for Ruby. Available as the 'bitset' gem.
Installation
Usually you want to do this:
gem install bitset
But if you want the latest patches or want to work on it yourself, you may want to do this:
git clone git://github.com/ericboesch/bitset.git
cd bitset
rake build
gem install pkg/bitset-<version>.gem
Usage
You create a bitset like this:
>> Bitset.new(8)
=> 00000000
Here we created an 8-bit bitset. All bits are initialized to 0.
We can also create a bitset based on a string of ones and zeros.
>> Bitset.from_s('00010001')
=> 00010001
or from an array. Falsey values (false and nil) are converted to zeroes; all other values, including 0 and "", are converted to ones.
>> Bitset.new [false, nil, 3, 0]
=> 0011
To input an array of ones and zeroes:
>> Bitset.new([0,1,1,0].map(&:positive?))
=> 0110
Obviously you can also set and clear bits...
>> bitset = Bitset.new(8)
=> 00000000
>> bitset[3] = true
=> 00010000
>> bitset[3] = false
=> 00000000
>> bitset.set(1, 3, 5, 7)
=> 01010101
>> bitset.clear(1, 5)
=> 00010001
Arrays of Integers can also be passed to #clear and #set (c/o brendon9x).
The point of a bitset is to be, effectively, an array of single bits. It should support basic set and bitwise operations. So, let's look at a few of those.
>> a = Bitset.from_s('00001111')
=> 00001111
>> b = Bitset.from_s('01010101')
=> 01010101
>> a & b
=> 00000101
>> a | b
=> 01011111
>> b - a
=> 01010000
>> a ^ b
=> 01011010
>> ~a
=> 11110000
>> a.hamming(b)
=> 4
>> a.cardinality
=> 4
>> a.reverse
=> 11110000
# Tell whether all of the given bit numbers are set
>> a.set? 6
=> true
# Return a new Bitset composed of bits #1, #3, #5, #4, and #1
# again. Unlike Array#values_at, this function currently only
# accepts an array of Fixnums as its argument.
>> a.values_at [1,3,5,4,1]
=> 00110
# Tell whether all of the given bit numbers are clear
>> a.clear? 1,3,5
=> false
# Tell whether all bits are clear
>> a.empty?
=> false
# Pass all bits to the block
>> b.each { |v| puts v }
=> false
true
false
...
# Pass the positions of all set bits to the block
>> b.each_set { |bit| puts bit }
=> 1
3
5
7
# Return an array of the positions of all set bits
>> b.each_set # AKA b.to_a
=> [1, 3, 5, 7]
# b.each_set(index) == b.each_set[index], but faster.
>> b.each_set(-3) # Negative index wraps around.
=> 3
# b.each_set(index, len) == b.each_set[index, len], but faster.
>> b.each_set(2,2) # Block is also allowed
=> [5,7]
# The following methods modify a Bitset in place very quickly:
>> a.intersect!(b) # like a &= b
>> a.union!(b) # like a |= b
>> a.difference!(b) # like a -= b
>> a.xor!(b) # like a ^= b
>> a.reset! # Zeroes all bits
# Above, "like" does not mean "identical to." a |= b creates a new
# Bitset object. a.union!(b) changes an existing object which
# affects all variables that point to the same object.
# Attempting to apply bitwise binary operators or their in-place
# equivalents between bitsets of different sizes will raise an
# ArgumentError.
>> b.to_binary_array
=> [0, 1, 0, 1, 0, 1, 0, 1]
# b.dup and b.clone are also available.
# Marshal.dump and Marshal.load are also supported. If you want to
# save a few bytes and don't need Marshal.load to work, you can
# use #pack and Bitset.unpack instead.
Contributing
The best way to contribute is to fork the project on GitHub, make your changes, and send a pull request. This is always much appreciated. If you want to mess around with the version numbers, gemspec, or anything like that feel free... But do it in separate commits so I can easily ignore them.
License
See LICENSE.txt.
