Merge pull request #1 from mceachen/master

TLC

Author: Peter Cooper

Gemfile

@@ -1,4 +1,2 @@
 source "http://rubygems.org"
-
-# Specify your gem's dependencies in bitarray.gemspec
 gemspec

Gemfile.lock

@@ -0,0 +1,20 @@
+PATH
+  remote: .
+  specs:
+    bitarray (0.0.5)
+
+GEM
+  remote: http://rubygems.org/
+  specs:
+    rake (0.9.2.2)
+    test-unit (2.4.5)
+    yard (0.7.4)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  bitarray!
+  rake
+  test-unit
+  yard

README.md

@@ -2,32 +2,57 @@
 
 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 .. I will review the code and bring the docs up to date in due course.
+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 .. I will review the code and bring the docs up to date in due course.
 
 ## Installation
 
-    gem install bitarray
+```ruby
+gem install bitarray
+```
 
 ## Examples
 
 To use:
 
-    require 'bitarray'
+```ruby
+require 'bitarray'
+```
 
-Create a bit field 1000 bits wide:
+Create a bit array 1000 bits wide:
 
-    ba = BitArray.new(1000)
+```ruby
+ba = BitArray.new(1000)
+```
 
 Setting and reading bits:
 
-    ba[100] = 1
-    ba[100]    .. => 1
-    ba[100] = 0
+```ruby
+ba[100] = 1
+ba[100]
+#=> 1
+
+ba[100] = 0
+ba[100]
+#=> 0
+```
 
 More:
 
-    ba.to_s = "10101000101010101"  (example)
-    ba.total_set         .. => 10  (example - 10 bits are set to "1")
+```ruby
+ba = BitArray.new(20)
+[1,3,5,9,11,13,15].each { |i| ba[i] = 1 }
+ba.to_s
+#=> "01010100010101010000"
+ba.total_set
+#=> 7
+```
+
+## History
+- v5 (added support for flags being on by default, instead of off)
+- v4 (fixed bug where setting 0 bits to 0 caused a set to 1)
+- v3 (supports dynamic bitwidths for array elements.. now doing 32 bit widths default)
+- v2 (now uses 1 << y, rather than 2 ** y .. it's 21.8 times faster!)
+- v1 (first release)
 
 ## License
 

bitarray.gemspec

@@ -1,9 +1,11 @@
 # -*- encoding: utf-8 -*-
 $:.push File.expand_path("../lib", __FILE__)
 
+require 'bitarray'
+
 Gem::Specification.new do |s|
   s.name        = "bitarray"
-  s.version     = "0.0.1"
+  s.version     = BitArray::VERSION
   s.authors     = ["Peter Cooper"]
   s.email       = ["git@peterc.org"]
   s.homepage    = "https://github.com/peterc/bitarray"
@@ -16,4 +18,8 @@ Gem::Specification.new do |s|
   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"]
+  
+  s.add_development_dependency "rake"
+  s.add_development_dependency "yard"
+  s.add_development_dependency "test-unit"
 end

lib/bitarray.rb

@@ -1,14 +1,15 @@
 class BitArray
   attr_reader :size
   include Enumerable
-  
+  VERSION = "0.0.5"
   ELEMENT_WIDTH = 32
-  
-  def initialize(size)
+
+  def initialize(size, default_value = 0)
     @size = size
     @field = Array.new(((size - 1) / ELEMENT_WIDTH) + 1, 0)
+    @field.map!{|i| ~i} if (default_value == 1)
   end
-  
+
   # Set a bit (1/0)
   def []=(position, value)
     if value == 1
@@ -17,22 +18,22 @@ def []=(position, value)
       @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 }
+    @field.collect{|ea| ("%032b" % ea).reverse}.join[0..@size-1]
   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

test/test_bitarray.rb

@@ -2,61 +2,78 @@
 require "bitarray"
 
 class TestBitArray < Test::Unit::TestCase
+
   def setup
-    @public_bf = BitArray.new(1000)
+    @public_ba = 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]
+    @public_ba[100] = 1
+    assert_equal 1, @public_ba[100]
+    @public_ba[100] = 0
+    assert_equal 0, @public_ba[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]
+      @public_ba[index] = 1
+      assert_equal 1, @public_ba[index]
+      @public_ba[index] = 0
+      assert_equal 0, @public_ba[index]
     end
   end
-  
+
+  def test_random_side_effects
+    ba2 = BitArray.new(@public_ba.size, 1)
+
+    on = (@public_ba.size / 2).times.collect do
+      index = rand(@public_ba.size)
+      @public_ba[index] = 1
+      ba2[index] = 0
+      index
+    end
+    assert_equal(@public_ba.to_s, @public_ba.to_s_fast)
+
+    @public_ba.size.times do |i|
+      assert_equal(@public_ba[i], on.include?(i) ? 1 : 0)
+      assert_equal(ba2[i], on.include?(i) ? 0 : 1)
+    end
+  end
+
   def test_multiple_setting
     1.upto(999) do |pos|
-      2.times { @public_bf[pos] = 1 }
-      assert_equal 1, @public_bf[pos]
+      2.times { @public_ba[pos] = 1 }
+      assert_equal 1, @public_ba[pos]
     end
   end
 
   def test_multiple_unsetting
     1.upto(999) do |pos|
-      2.times { @public_bf[pos] = 0 }
-      assert_equal 0, @public_bf[pos]
+      2.times { @public_ba[pos] = 0 }
+      assert_equal 0, @public_ba[pos]
     end
   end
-  
+
   def test_size
-    assert_equal 1000, @public_bf.size
+    assert_equal 1000, @public_ba.size
   end
-  
+
   def test_to_s
-    bf = BitArray.new(10)
-    bf[1] = 1
-    bf[5] = 1
-    assert_equal "0100010000", bf.to_s
+    ba = BitArray.new(35)
+    [1, 5, 6, 7, 10, 16, 33].each{|i|ba[i] = 1}
+    assert_equal "01000111001000001000000000000000010", ba.to_s
   end
-  
+
   def test_total_set
-    bf = BitArray.new(10)
-    bf[1] = 1
-    bf[5] = 1
-    assert_equal 2, bf.total_set
+    ba = BitArray.new(10)
+    ba[1] = 1
+    ba[5] = 1
+    assert_equal 2, ba.total_set
   end
-end
+end