diff --git a/.gitignore b/.gitignore
index 6bad8bb..33c6e83 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,11 +1,6 @@
-/ext/*.o
-/ext/*.bundle
-/ext/*.so
-/ext/*.dll
-/ext/mkmf.log
+/tmp
 /lib/simple_mmap/*.bundle
 /lib/simple_mmap/*.so
 /lib/simple_mmap/*.dll
-/ext/Makefile
 /pkg
 /doc/*
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..f939f55
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,6 @@
+language: ruby
+rvm:
+  - 2.0.0
+  - 1.9.3
+  - 1.9.2
+  - 1.8.7
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 0000000..8e2ab11
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,4 @@
+source 'https://rubygems.org'
+
+# Specify your gem's dependencies in simple_mmap.gemspec
+gemspec
diff --git a/Rakefile b/Rakefile
index a2ceecc..a81bac4 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,38 +1,15 @@
-# encoding: utf-8
+require "bundler/gem_tasks"
 
-require 'rubygems'
-require 'hoe'
-require './lib/simple_mmap/version.rb'
-require "rake/clean"
-
-Hoe.new('simple_mmap', SimpleMmap::VERSION) do |p|
-  p.rubyforge_name = 'simple-mmap'
-  p.developer('Johan Sørensen', 'johan@johansorensen.com')
-  p.spec_extras = {
-    "extensions" => ["Rakefile"]
-  }
-end
-
-DLEXT = Config::CONFIG['DLEXT']
-
-file 'ext/Makefile' => FileList['ext/{*.c,*.h,*.rb}'] do
-  chdir('ext') { ruby 'extconf.rb' }
+require 'rake/extensiontask'
+Rake::ExtensionTask.new('simple_mmap') do |ext|
+  ext.name = "mapped_file"
+  ext.lib_dir = File.join('lib', 'simple_mmap')
 end
-CLEAN.include 'ext/Makefile', 'ext/mkmf.log'
 
-file "ext/mapped_file.#{DLEXT}" => FileList['ext/Makefile', 'ext/*.{c,h,rb}'] do |f|
-  sh 'cd ext && make'
+require 'rake/testtask'
+Rake::TestTask.new(:test => :compile) do |test|
+  test.libs << 'ext'
+  test.verbose = true
 end
-CLEAN.include 'ext/*.{o,bundle,so,dll}'
-
-file "lib/simple_mmap/mapped_file.#{DLEXT}" => "ext/mapped_file.#{DLEXT}" do |f|
-  cp f.prerequisites, "lib/simple_mmap/", :preserve => true
-end
-#CLEAN.include "lib/simple_mmap/mapped_file.#{DLEXT}"
-
-desc 'Build the mapped_file extension'
-task :build => "lib/simple_mmap/mapped_file.#{DLEXT}"
-
-task :test => [:build]
 
 task :default => :test
diff --git a/VERSION b/VERSION
new file mode 100644
index 0000000..65087b4
--- /dev/null
+++ b/VERSION
@@ -0,0 +1 @@
+1.1.4
diff --git a/ext/extconf.rb b/ext/extconf.rb
deleted file mode 100644
index f4fe914..0000000
--- a/ext/extconf.rb
+++ /dev/null
@@ -1,5 +0,0 @@
-require 'mkmf'
-
-dir_config('mapped_file')
-have_func('mmap')
-create_makefile('mapped_file')
diff --git a/ext/simple_mmap/extconf.rb b/ext/simple_mmap/extconf.rb
new file mode 100644
index 0000000..c41cbc3
--- /dev/null
+++ b/ext/simple_mmap/extconf.rb
@@ -0,0 +1,4 @@
+require 'mkmf'
+
+have_func('mmap')
+create_makefile('simple_mmap/mapped_file')
diff --git a/ext/mapped_file.c b/ext/simple_mmap/mapped_file.c
similarity index 61%
rename from ext/mapped_file.c
rename to ext/simple_mmap/mapped_file.c
index d835ab5..c917c44 100644
--- a/ext/mapped_file.c
+++ b/ext/simple_mmap/mapped_file.c
@@ -28,11 +28,31 @@
 #include <unistd.h>
 #include "ruby.h"
 
+#ifndef NUM2SIZET
+#  include <limits.h>
+#  include <stdint.h>
+#  if SIZE_MAX > ULONG_MAX
+#    define NUM2SIZET NUM2ULL
+#    define SIZET2NUM ULONG2NUM
+#  elif SIZE_MAX > UINT_MAX
+#    define NUM2SIZET NUM2ULONG
+#    define SIZET2NUM ULONG2NUM
+#  elif SIZE_MAX > USHRT_MAX
+#    define NUM2SIZET NUM2UINT
+#    define SIZET2NUM UINT2NUM
+#  else
+#    define NUM2SIZET NUM2USHORT
+#    define SIZET2NUM USHORT2NUM
+#  endif
+#endif
+
 // a memory mapped file
 typedef struct {  
-	int fd;
+  int fd;
   caddr_t map;
-	size_t len;
+  size_t len;
+  caddr_t read_base;
+  size_t read_len;
 } simple_mmap_map;
 
 static VALUE mod_simple_mmap;
@@ -45,7 +65,7 @@ static VALUE sm_map_data;
  *
  * mmap() the file at +path+
  */
-static VALUE sm_mapped_file_initialize(VALUE vself, VALUE filename)
+static VALUE sm_mapped_file_initialize(int argc, VALUE *argv, VALUE vself)
 {
   int fd = -1;
   size_t length;
@@ -54,6 +74,15 @@ static VALUE sm_mapped_file_initialize(VALUE vself, VALUE filename)
   VALUE vsm_map;
   simple_mmap_map *sm_map;
   
+  VALUE filename, voffset, vlength;
+  off_t offset, offset_mod;
+
+  rb_scan_args(argc, argv, "12", &filename, &voffset, &vlength);
+  if (!NIL_P(voffset) && NUM2LL(voffset) < 0)
+    rb_raise(rb_eRangeError, "offset out of range: %lld", NUM2LL(voffset));
+  if (!NIL_P(vlength) && NUM2LL(vlength) < 0)
+    rb_raise(rb_eRangeError, "length out of range: %lld", NUM2LL(vlength));
+
   fd = open(RSTRING_PTR(filename), O_RDONLY);
   if (fd == -1) {
     rb_raise(rb_eArgError, "Failed to open file %s", RSTRING_PTR(filename));
@@ -65,10 +94,15 @@ static VALUE sm_mapped_file_initialize(VALUE vself, VALUE filename)
     rb_raise(rb_eArgError, "Failed to stat file %s", RSTRING_PTR(filename));
     close(fd);
   }
-  length = st.st_size;
+  offset = NIL_P(voffset) ? 0 : NUM2SIZET(voffset);
+  length = NIL_P(vlength) ? st.st_size : NUM2SIZET(vlength);
+  if (offset + length > st.st_size) length = st.st_size - offset;
+  offset_mod = offset % sysconf(_SC_PAGESIZE);
+  offset = offset - offset_mod;
+  length = length + offset_mod;
   
   // do the mmap
-  base = mmap(NULL, length, PROT_READ, MAP_SHARED, fd, 0);
+  base = mmap(NULL, length, PROT_READ, MAP_SHARED, fd, offset);
   if (base == (caddr_t) -1) {
     rb_raise(rb_eArgError, "Failed to mmap file %s", RSTRING_PTR(filename));
     close(fd);
@@ -80,6 +114,8 @@ static VALUE sm_mapped_file_initialize(VALUE vself, VALUE filename)
   sm_map->fd = fd;
   sm_map->map = base;
   sm_map->len = length;
+  sm_map->read_base = base + offset_mod;
+  sm_map->read_len = length - offset_mod;
   rb_ivar_set(vself, rb_intern("@mmap_data"), vsm_map);
   
   return Qnil;
@@ -109,41 +145,50 @@ static VALUE sm_mapped_file_close(VALUE vself)
 }
 
 /*
- * Document-method: close
+ * Document-method: read_window_data
  * call-seq: obj.read_window_data(offset, length)
  *
  * Read +length+ bytes starting at +offset+
  */
 static VALUE sm_mapped_file_read_window_data(VALUE vself, VALUE voffset, VALUE vlength) 
 {
-  size_t offset = NUM2INT(voffset);
-  size_t length = NUM2INT(vlength);
-  char buff[length];
+  size_t offset, length;
   VALUE vsm_map;
   simple_mmap_map *sm_map;
   
-  sm_map = ALLOC(simple_mmap_map);
+  if (NUM2LL(voffset) < 0) return Qnil;
+  if (NUM2LL(vlength) < 0) rb_raise(rb_eRangeError, "length out of range: %lld", NUM2LL(vlength));
+  offset = NUM2SIZET(voffset);
+  length = NUM2SIZET(vlength);
+
   vsm_map = rb_ivar_get(vself, rb_intern("@mmap_data"));
   Data_Get_Struct(vsm_map, simple_mmap_map, sm_map);
   
-  if (offset > sm_map->len) {
-    return Qnil;
-  }
-  
-  size_t curr;
-  curr = offset;
-  size_t i;
-  for(i = 0; i < length; ++i) {
-    //printf("i=%i offset=%i length=%i curr=%i map->len=%i\n", i, offset, length, curr, sm_map->len);
-    if ((curr + i) > sm_map->len)
-      break;
-    buff[i] = sm_map->map[curr++];
+  if (offset > sm_map->read_len) return Qnil;
+
+  // If the range overflows, return part that overlaps
+  if ((offset + length) > sm_map->read_len) {
+    length = sm_map->read_len - offset;
   }
-  
-  if ((offset + length) > sm_map->len)
-    return rb_str_new(buff, ((offset+length) - sm_map->len)-1);
-      
-  return rb_str_new(buff, length);
+
+  return rb_str_new(sm_map->read_base + offset, length);
+}
+
+/*
+ * Document-method: size
+ * call-seq: obj.size
+ *
+ * Return size of mapped file
+ */
+
+static VALUE sm_mapped_file_size(VALUE vself)
+{
+  VALUE vsm_map;
+  simple_mmap_map *sm_map;
+
+  vsm_map = rb_ivar_get(vself, rb_intern("@mmap_data"));
+  Data_Get_Struct(vsm_map, simple_mmap_map, sm_map);
+  return SIZET2NUM(sm_map->read_len);
 }
 
 void Init_mapped_file()
@@ -151,9 +196,10 @@ void Init_mapped_file()
   mod_simple_mmap = rb_define_module("SimpleMmap");
   
   sm_mapped_file = rb_define_class_under(mod_simple_mmap, "MappedFile", rb_cObject);
-  rb_define_private_method(sm_mapped_file, "initialize", sm_mapped_file_initialize, 1);
+  rb_define_private_method(sm_mapped_file, "initialize", sm_mapped_file_initialize, -1);
   rb_define_method(sm_mapped_file, "close", sm_mapped_file_close, 0);
   rb_define_method(sm_mapped_file, "read_window_data", sm_mapped_file_read_window_data, 2);
+  rb_define_method(sm_mapped_file, "size", sm_mapped_file_size, 0);
   
   sm_map_data = rb_define_class_under(sm_mapped_file, "MmapData", rb_cObject);
 }
diff --git a/lib/simple_mmap.rb b/lib/simple_mmap.rb
index 972ea91..cfbde3e 100644
--- a/lib/simple_mmap.rb
+++ b/lib/simple_mmap.rb
@@ -1,4 +1,4 @@
-# Copyright (c) 2009 Johan Sørensen
+# Copyright (c) 2009-2016 Johan Sørensen
 # 
 # Permission is hereby granted, free of charge, to any person obtaining
 # a copy of this software and associated documentation files (the
diff --git a/lib/simple_mmap/file_window.rb b/lib/simple_mmap/file_window.rb
index b6050f1..b6caa4b 100644
--- a/lib/simple_mmap/file_window.rb
+++ b/lib/simple_mmap/file_window.rb
@@ -25,10 +25,10 @@ module SimpleMmap
   class FileWindow
     # Create a mmap'ed window for file at +path+
     # You are responsible for closing it when you're done using #close
-    def initialize(path)
+    def initialize(path, offset = nil, length = nil)
       @path = path
       @offset = 0
-      @mmap = SimpleMmap::MappedFile.new(@path)
+      @mmap = SimpleMmap::MappedFile.new(@path, offset, length)
     end
     attr_reader :path, :offset
     
@@ -70,11 +70,11 @@ def [](*index)
         offset = index
         length = 0
       when Range
-        offset = index.begin
-        length = index.end - index.begin
-        unless index.exclude_end?
-          length += 1
-        end
+        offset = index.begin < 0 ? index.begin + @mmap.size : index.begin
+        return nil if offset < 0 or offset > @mmap.size
+        length = (index.end < 0 ? index.end + @mmap.size : index.end) - offset
+        length += 1 unless index.exclude_end?
+        return '' if length <= 0
       end
       
       @offset = offset + length
@@ -92,5 +92,10 @@ def read(length)
       @offset += length
       data
     end
+
+    # Return size of mapped file
+    def size
+      @mmap.size
+    end
   end
 end
diff --git a/lib/simple_mmap/version.rb b/lib/simple_mmap/version.rb
index 539e453..ec55846 100644
--- a/lib/simple_mmap/version.rb
+++ b/lib/simple_mmap/version.rb
@@ -1,24 +1,3 @@
-# Copyright (c) 2009 Johan Sørensen
-# 
-# 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.
-
 module SimpleMmap
-  VERSION = '1.0.0'
+  VERSION = "1.2"
 end
diff --git a/simple-mmap.gemspec b/simple-mmap.gemspec
new file mode 100644
index 0000000..9d067ea
--- /dev/null
+++ b/simple-mmap.gemspec
@@ -0,0 +1,26 @@
+# coding: utf-8
+lib = File.expand_path('../lib', __FILE__)
+$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
+require 'simple_mmap/version'
+
+Gem::Specification.new do |spec|
+  spec.name          = "simple-mmap"
+  spec.version       = SimpleMmap::VERSION
+  spec.authors       = ["Johan Sørensen", "Pieter Noordhuis", "TAKADA Daisuke"]
+  spec.email         = ["pcnoordhuis@gmail.com", "shoulderpower@gmail.com"]
+#  spec.description   = %q{TODO: Write a gem description}
+  spec.description   = %q{A simplistic interface for reading memory mapped files}
+  spec.summary       = %q{A simplistic interface for reading memory mapped files}
+  spec.homepage      = "http://github.com/pietern/simple-mmap"
+  spec.license       = "MIT"
+
+  spec.files         = `git ls-files`.split($/)
+  spec.executables   = spec.files.grep(%r{^bin/}) { |f| File.basename(f) }
+  spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
+  spec.require_paths = ["ext", "lib"]
+  spec.extensions << 'ext/simple_mmap/extconf.rb'
+
+  spec.add_development_dependency "bundler", "~> 1.3"
+  spec.add_development_dependency "rake"
+  spec.add_development_dependency 'rake-compiler', '>= 0.7.0'
+end
diff --git a/test/test_file_window.rb b/test/test_file_window.rb
index 77d18a4..0ae42e5 100644
--- a/test/test_file_window.rb
+++ b/test/test_file_window.rb
@@ -5,7 +5,7 @@
 class TestFileWindow < Test::Unit::TestCase
   def setup
     @file = Tempfile.new("TestFileWindow.data")
-    File.open(@file.path, "w"){|f| f.puts(('a'..'z').to_a.join) }
+    File.open(@file.path, "w"){|f| f.write(('a'..'z').to_a.join) }
     @fw = SimpleMmap::FileWindow.new(@file.path)
   end
   
@@ -39,6 +39,19 @@ def test_get_single_byte_at_current_offset_with_index
     assert_equal 1, @fw.offset
   end
   
+  def test_get_bytes_past_length
+    assert_equal "z", @fw[25, 10]
+  end
+
+  def test_get_all_bytes
+    assert_equal ('a'..'z').to_a.join, @fw[0, 26]
+  end
+
+  def test_nil_on_negative_index
+    assert_equal nil, @fw[-1]
+    assert_equal nil, @fw[-1, 2]
+  end
+
   def test_get_from_x_to_y_with_index_comma_notation
     assert_equal "cde", @fw[2, 3]
     assert_equal 5, @fw.pos
@@ -59,4 +72,8 @@ def test_read
     assert_equal "abc", @fw.read(3)
     assert_equal 3, @fw.offset
   end
+
+  def test_size
+    assert_equal 26, @fw.size
+  end
 end