Initial commit

Author: peterc

.gitignore

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+*.gem
+.bundle
+Gemfile.lock
+pkg/*

Gemfile

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+source "http://rubygems.org"
+
+# Specify your gem's dependencies in bitarray.gemspec
+gemspec

README.md

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+# BitArray: A simple bit array/bit field library in pure Ruby
+
+Basic, pure Ruby bit field. Pretty fast (for what it is) and memory efficient. Works well for Bloom filters (the reason I wrote it).
+
+Written in 2007 and not updated since then, just bringing it on to GitHub by user request. It used to be called Bitfield and was hosted at http://snippets.dzone.com/posts/show/4234
+
+## Examples
+
+Create a bit field 1000 bits wide
+    bf = BitField.new(1000)
+
+Setting and reading bits
+    bf[100] = 1
+    bf[100]    .. => 1
+    bf[100] = 0
+
+More
+    bf.to_s = "10101000101010101"  (example)
+    bf.total_set         .. => 10  (example - 10 bits are set to "1")
+
+## License
+
+MIT licensed. Copyright 2007-2012 Peter Cooper, yada yada.

Rakefile

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+require "bundler/gem_tasks"
+require "rake/testtask"
+
+Rake::TestTask.new      # defaults are fine for now
+task :default => :test

bitarray.gemspec

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+# -*- encoding: utf-8 -*-
+$:.push File.expand_path("../lib", __FILE__)
+
+Gem::Specification.new do |s|
+  s.name        = "bitarray"
+  s.version     = "0.0.1"
+  s.authors     = ["Peter Cooper"]
+  s.email       = ["git@peterc.org"]
+  s.homepage    = "https://github.com/peterc/bitarray"
+  s.summary     = %q{A simple, pure Ruby bit array implementation.}
+  s.description = %q{A simple, pure Ruby bit array implementation.}
+
+  s.rubyforge_project = "bitarray"
+
+  s.files         = `git ls-files`.split("\n")
+  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
+  s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
+  s.require_paths = ["lib"]
+end

lib/bitarray.rb

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+class BitArray
+  attr_reader :size
+  include Enumerable
+  
+  ELEMENT_WIDTH = 32
+  
+  def initialize(size)
+    @size = size
+    @field = Array.new(((size - 1) / ELEMENT_WIDTH) + 1, 0)
+  end
+  
+  # Set a bit (1/0)
+  def []=(position, value)
+    if value == 1
+      @field[position / ELEMENT_WIDTH] |= 1 << (position % ELEMENT_WIDTH)
+    elsif (@field[position / ELEMENT_WIDTH]) & (1 << (position % ELEMENT_WIDTH)) != 0
+      @field[position / ELEMENT_WIDTH] ^= 1 << (position % ELEMENT_WIDTH)
+    end
+  end
+  
+  # Read a bit (1/0)
+  def [](position)
+    @field[position / ELEMENT_WIDTH] & 1 << (position % ELEMENT_WIDTH) > 0 ? 1 : 0
+  end
+  
+  # Iterate over each bit
+  def each(&block)
+    @size.times { |position| yield self[position] }
+  end
+  
+  # Returns the field as a string like "0101010100111100," etc.
+  def to_s
+    inject("") { |a, b| a + b.to_s }
+  end
+  
+  # Returns the total number of bits that are set
+  # (The technique used here is about 6 times faster than using each or inject direct on the bitfield)
+  def total_set
+    @field.inject(0) { |a, byte| a += byte & 1 and byte >>= 1 until byte == 0; a }
+  end
+end

test/test_bitarray.rb

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+require "test/unit"
+require "bitarray"
+
+class TestBitArray < Test::Unit::TestCase
+  def setup
+    @public_bf = BitArray.new(1000)
+  end
+  
+  def test_basic
+    assert_equal 0, BitArray.new(100)[0]
+    assert_equal 0, BitArray.new(100)[1]
+  end
+  
+  def test_setting_and_unsetting
+    @public_bf[100] = 1
+    assert_equal 1, @public_bf[100]
+    @public_bf[100] = 0
+    assert_equal 0, @public_bf[100]
+  end
+
+  def test_random_setting_and_unsetting
+    100.times do
+      index = rand(1000)
+      @public_bf[index] = 1
+      assert_equal 1, @public_bf[index]
+      @public_bf[index] = 0
+      assert_equal 0, @public_bf[index]
+    end
+  end
+  
+  def test_multiple_setting
+    1.upto(999) do |pos|
+      2.times { @public_bf[pos] = 1 }
+      assert_equal 1, @public_bf[pos]
+    end
+  end
+
+  def test_multiple_unsetting
+    1.upto(999) do |pos|
+      2.times { @public_bf[pos] = 0 }
+      assert_equal 0, @public_bf[pos]
+    end
+  end
+  
+  def test_size
+    assert_equal 1000, @public_bf.size
+  end
+  
+  def test_to_s
+    bf = BitArray.new(10)
+    bf[1] = 1
+    bf[5] = 1
+    assert_equal "0100010000", bf.to_s
+  end
+  
+  def test_total_set
+    bf = BitArray.new(10)
+    bf[1] = 1
+    bf[5] = 1
+    assert_equal 2, bf.total_set
+  end
+end