Ecosyste.ms: Awesome
An open API service indexing awesome lists of open source software.
https://github.com/pboling/flag_shih_tzu
Bit fields for ActiveRecord
https://github.com/pboling/flag_shih_tzu
Last synced: 27 days ago
JSON representation
Bit fields for ActiveRecord
- Host: GitHub
- URL: https://github.com/pboling/flag_shih_tzu
- Owner: pboling
- License: mit
- Created: 2009-03-11T12:00:28.000Z (over 15 years ago)
- Default Branch: master
- Last Pushed: 2023-09-12T19:49:09.000Z (about 1 year ago)
- Last Synced: 2024-10-04T19:17:15.664Z (about 1 month ago)
- Language: Ruby
- Homepage: http://railsbling.com/flag_shih_tzu
- Size: 426 KB
- Stars: 495
- Watchers: 9
- Forks: 64
- Open Issues: 11
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
Awesome Lists containing this project
README
# FlagShihTzu
Bit fields for ActiveRecord
| Project | FlagShihTzu |
|------------------------ | ----------------- |
| gem name | flag_shih_tzu |
| license | [](https://opensource.org/licenses/MIT) |
| expert support | [](https://www.codementor.io/peterboling?utm_source=github&utm_medium=button&utm_term=peterboling&utm_campaign=github) |
| download rank | [](https://rubygems.org/gems/flag_shih_tzu) [](https://rubygems.org/gems/flag_shih_tzu) |
| version | [](http://badge.fury.io/rb/flag_shih_tzu) |
| dependencies | [](https://depfu.com/github/pboling/flag_shih_tzu?project_id=2685) |
| code quality | [](https://codeclimate.com/github/pboling/flag_shih_tzu) [](https://houndci.com) |
| inline documenation | [](http://inch-ci.org/github/pboling/flag_shih_tzu) |
| continuous integration | [](https://travis-ci.org/pboling/flag_shih_tzu) |
| test coverage | [](https://coveralls.io/r/pboling/flag_shih_tzu) |
| homepage | [https://github.com/pboling/flag_shih_tzu][homepage] |
| documentation | [http://rdoc.info/github/pboling/flag_shih_tzu/frames][documentation] |
| live chat | [](https://gitter.im/pboling/flag_shih_tzu?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge) |
| Spread ~♡ⓛⓞⓥⓔ♡~ | [🌏](https://about.me/peter.boling), [👼](https://angel.co/peter-boling), [:shipit:](http://coderwall.com/pboling), [](http://twitter.com/galtzo), [🌹](https://nationalprogressiveparty.org) |
Table of Contents
=================
* [FlagShihTzu](#flagshihtzu)
* [Summary](#summary)
* [Prerequisites](#prerequisites)
* [Compatibility Matrix](#compatibility-matrix)
* [Installation](#installation)
* [Rails 2.x](#rails-2x)
* [Rails 3](#rails-3)
* [Usage](#usage)
* [Defaults (Important)](#defaults-important)
* [Database Migration](#database-migration)
* [Adding to the Model](#adding-to-the-model)
* [Bit Fields: How it stores the values](#bit-fields-how-it-stores-the-values)
* [Using a custom column name](#using-a-custom-column-name)
* [Generated boolean patterned instance methods](#generated-boolean-patterned-instance-methods)
* [Callbacks and Validations](#callbacks-and-validations)
* [Generated class methods](#generated-class-methods)
* [Generated named scopes](#generated-named-scopes)
* [Examples for using the generated methods](#examples-for-using-the-generated-methods)
* [Support for manually building conditions](#support-for-manually-building-conditions)
* [Choosing a query mode](#choosing-a-query-mode)
* [Updating flag column by raw sql](#updating-flag-column-by-raw-sql)
* [Skipping flag column check](#skipping-flag-column-check)
* [Running the gem tests](#running-the-gem-tests)
* [Authors](#authors)
* [How you can help!](#how-you-can-help)
* [Contributing](#contributing)
* [Versioning](#versioning)
* [2012 Change of Ownership and 0.3.X Release Notes](#2012-change-of-ownership-and-03x-release-notes)
* [Alternatives](#alternatives)
* [License](#license)
## Summary
An extension for [ActiveRecord](https://rubygems.org/gems/activerecord)
to store a collection of boolean attributes in a single integer column
as a [bit field][bit_field].
This gem lets you use a single integer column in an ActiveRecord model
to store a collection of boolean attributes (flags). Each flag can be used
almost in the same way you would use any boolean attribute on an
ActiveRecord object.
The benefits:
* No migrations needed for new boolean attributes. This helps a lot
if you have very large db-tables, on which you want to avoid `ALTER TABLE`
whenever possible.
* Only the one integer column needs to be indexed.
* [Bitwise Operations][bitwise_operation] are fast!
Using FlagShihTzu, you can add new boolean attributes whenever you want,
without needing any migration. Just add a new flag to the `has_flags` call.
What is a ["Shih Tzu"](http://en.wikipedia.org/wiki/Shih_Tzu)?
## Prerequisites
The gem is actively being tested against:
* MySQL, PostgreSQL and SQLite3 databases (Both Ruby and JRuby adapters)
* ActiveRecord versions 2.3.x, 3.0.x, 3.1.x, 3.2.x, 4.0.x, 4.1.x, 4.2.x, 5.0.x, 5.1.x, 5.2.x
* Ruby 1.9.3, 2.0.0, 2.1.10, 2.2.10, 2.3.7, 2.4.4, 2.5.1, jruby-1.7.x, jruby-9.1.x
* Travis tests the supported builds. See [.travis.yml](https://github.com/pboling/flag_shih_tzu/blob/master/.travis.yml) for the matrix.
* All of the supported builds can also be run locally using the `wwtd` gem.
* Forthcoming flag_shih_tzu v1.0 will only support Ruby 2.2+, JRuby-9.1+ and Rails 4.2+
### Compatibility Matrix
| Ruby / Active Record | 2.3.x | 3.0.x | 3.1.x | 3.2.x | 4.0.x | 4.1.x | 4.2.x | 5.0.x | 5.1.x | 5.2.x |
|:---------------------:|:-----:|:-----:|:-----:|:-----:|:-----:|:-----:|:-----:|:-----:|:-----:|:-----:|
| 1.9.3 | ✓ | ✓ | ✓ | ✓ | | | | | | |
| 2.0.0 | | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | | | |
| 2.1.x | | | | ✓ | ✓ | ✓ | ✓ | | | |
| 2.2.0-2.2.1 | | | | ✓ | ✓ | ✓ | ✓ | | | |
| 2.2.2+ | | | | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| 2.3.x | | | | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| 2.4.x | | | | | | | ✓ | ✓ | ✓ | ✓ |
| 2.5.x | | | | | | | ✓ | ✓ | ✓ | ✓ |
| jruby-1.7.x | ? | ? | ✓ | ✓ | ✓ | ✓ | ✓ | | | |
| jruby-9.1 | | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| jruby-9.2 | | | | | | | ✓ | ✓ | ✓ | ✓ |
* Notes
- JRuby 1.7.x aims for MRI 1.9.3 compatibility
- `?` indicates incompatible due to 2 failures in the test suite.
- JRuby 9.1 aims for MRI 2.2 compatibility
- JRuby 9.2 aims for MRI 2.5 compatibility
- Forthcoming flag_shih_tzu v1.0 will only support Ruby 2.2+, JRuby-9.1+ and Rails 4.2+
**Legacy**
* Ruby 1.8.7 compatibility is in the [0.2.X branch](https://github.com/pboling/flag_shih_tzu/tree/0.2.X) and no further releases are expected. If you need a patch submit a pull request.
* Ruby 1.9.3, 2.0.0, 2.1.x, and 2.2.x compatibility is still current on master, and the 0.3.x series releases, but those EOL'd Rubies, and any others that become EOL'd in the meantime, will not be supported in the next major release, version 1.0.
## Installation
### Rails 2.x
In environment.rb:
```ruby
config.gem 'flag_shih_tzu'
```
Then:
$ rake gems:install # use sudo if necessary
### Rails 3
In Gemfile:
```ruby
gem 'flag_shih_tzu'
```
Then:
$ bundle install
## Usage
FlagShihTzu assumes that your ActiveRecord model already has an [integer field][bit_field]
to store the flags, which should be defined to not allow `NULL` values and
should have a default value of `0`.
### Defaults (Important)
* Due to the default of `0`, *all flags* are initially set to "false").
* For a default of true it will probably be easier in the long run to negate the flag's meaning / name.
** Such as `switched_on` => `switched_off`
* If you **really** want a different, non-zero, default value for a flag column, proceed *adroitly* with a different sql default for the flag column.
### Database Migration
I like to document the intent of the `flags` column in the migration when I can...
```ruby
change_table :spaceships do |t|
t.integer :flags, :null => false, :default => 0 # flag_shih_tzu-managed bit field
# Effective booleans which will be stored on the flags column:
# t.boolean :warpdrive
# t.boolean :shields
# t.boolean :electrolytes
end
```
### Adding to the Model
```ruby
class Spaceship < ActiveRecord::Base
include FlagShihTzu
has_flags 1 => :warpdrive,
2 => :shields,
3 => :electrolytes
end
```
`has_flags` takes a hash. The keys must be positive integers and represent
the position of the bit being used to enable or disable the flag.
**The keys must not be changed once in use, or you will get incorrect results.**
That is why the plugin forces you to set them explicitly.
The values are symbols for the flags being created.
### Bit Fields: How it stores the values
As said, FlagShihTzu uses a single integer column to store the values for all
the defined flags as a [bit field][bitfield].
The bit position of a flag corresponds to the given key.
This way, we can use [bitwise operators][bit_operation] on the stored integer value to set, unset
and check individual flags.
`---+---+---+ +---+---+---`
| | | | | | | |
Bit position | 3 | 2 | 1 | | 3 | 2 | 1 |
(flag key) | | | | | | | |
`---+---+---+ +---+---+---`
| | | | | | | |
Bit value | 4 | 2 | 1 | | 4 | 2 | 1 |
| | | | | | | |
`---+---+---+ +---+---+---`
| e | s | w | | e | s | w |
| l | h | a | | l | h | a |
| e | i | r | | e | i | r |
| c | e | p | | c | e | p |
| t | l | d | | t | l | d |
| r | d | r | | r | d | r |
| o | s | i | | o | s | i |
| l | | v | | l | | v |
| y | | e | | y | | e |
| t | | | | t | | |
| e | | | | e | | |
| s | | | | s | | |
`---+---+---+ +---+---+---`
| 1 | 1 | 0 | = 4 ` 2 = 6 | 1 | 0 | 1 | = 4 ` 1 = 5
`---+---+---+ +---+---+---`
Read more about [bit fields][bit_field] here: http://en.wikipedia.org/wiki/Bit_field
### Using a custom column name
The default column name to store the flags is `flags`, but you can provide a
custom column name using the `:column` option. This allows you to use
different columns for separate flags:
```ruby
has_flags 1 => :warpdrive,
2 => :shields,
3 => :electrolytes,
:column => 'features'
has_flags 1 => :spock,
2 => :scott,
3 => :kirk,
:column => 'crew'
```
### Generated boolean patterned instance methods
Calling `has_flags`, as shown above on the 'features' column, creates the following instance methods
on Spaceship:
Spaceship#all_features # [:warpdrive, :shields, :electrolytes]
Spaceship#selected_features
Spaceship#select_all_features
Spaceship#unselect_all_features
Spaceship#selected_features=
Spaceship#warpdrive
Spaceship#warpdrive?
Spaceship#warpdrive=
Spaceship#not_warpdrive
Spaceship#not_warpdrive?
Spaceship#not_warpdrive=
Spaceship#warpdrive_changed?
Spaceship#has_warpdrive?
Spaceship#shields
Spaceship#shields?
Spaceship#shields=
Spaceship#not_shields
Spaceship#not_shields?
Spaceship#not_shields=
Spaceship#shields_changed?
Spaceship#has_shield?
Spaceship#electrolytes
Spaceship#electrolytes?
Spaceship#electrolytes=
Spaceship#not_electrolytes
Spaceship#not_electrolytes?
Spaceship#not_electrolytes=
Spaceship#electrolytes_changed?
Spaceship#has_electrolyte?
### Callbacks and Validations
Optionally, you can set the `:bang_methods` option to true to also define the bang methods:
Spaceship#electrolytes! # will save the bitwise equivalent of electrolytes = true on the record
Spaceship#not_electrolytes! # will save the bitwise equivalent of electrolytes = false on the record
which respectively enables or disables the electrolytes flag.
The `:bang_methods` does not save the records to the database, meaning it *cannot* engage validations and callbacks.
Alternatively, if you do want to *save a flag* to the database, while still avoiding validations and callbacks, use `update_flag!` which:
* sets a flag on a database record without triggering callbacks or validations
* optionally syncs the ruby instance with new flag value, by default it does not.
Example:
```ruby
update_flag!(flag_name, flag_value, update_instance = false)
```
### Generated class methods
Calling `has_flags` as shown above creates the following class methods
on Spaceship:
```ruby
Spaceship.flag_columns # [:features, :crew]
```
### Generated named scopes
The following named scopes become available:
```ruby
Spaceship.warpdrive # :conditions => "(spaceships.flags in (1,3,5,7))"
Spaceship.not_warpdrive # :conditions => "(spaceships.flags not in (1,3,5,7))"
Spaceship.shields # :conditions => "(spaceships.flags in (2,3,6,7))"
Spaceship.not_shields # :conditions => "(spaceships.flags not in (2,3,6,7))"
Spaceship.electrolytes # :conditions => "(spaceships.flags in (4,5,6,7))"
Spaceship.not_electrolytes # :conditions => "(spaceships.flags not in (4,5,6,7))"
```
If you do not want the named scopes to be defined, set the
`:named_scopes` option to false when calling `has_flags`:
```ruby
has_flags 1 => :warpdrive, 2 => :shields, 3 => :electrolytes, :named_scopes => false
```
In a Rails 3+ application, FlagShihTzu will use `scope` internally to generate
the scopes. The option on `has_flags` is still named `:named_scopes` however.
### Examples for using the generated methods
```ruby
enterprise = Spaceship.new
enterprise.warpdrive = true
enterprise.shields = true
enterprise.electrolytes = false
enterprise.save
if enterprise.shields?
# ...
end
Spaceship.warpdrive.find(:all)
Spaceship.not_electrolytes.count
```
### Support for manually building conditions
The following class methods may support you when manually building
ActiveRecord conditions:
```ruby
Spaceship.warpdrive_condition # "(spaceships.flags in (1,3,5,7))"
Spaceship.not_warpdrive_condition # "(spaceships.flags not in (1,3,5,7))"
Spaceship.shields_condition # "(spaceships.flags in (2,3,6,7))"
Spaceship.not_shields_condition # "(spaceships.flags not in (2,3,6,7))"
Spaceship.electrolytes_condition # "(spaceships.flags in (4,5,6,7))"
Spaceship.not_electrolytes_condition # "(spaceships.flags not in (4,5,6,7))"
```
These methods also accept a `:table_alias` option that can be used when
generating SQL that references the same table more than once:
```ruby
Spaceship.shields_condition(:table_alias => 'evil_spaceships') # "(evil_spaceships.flags in (2,3,6,7))"
```
### Choosing a query mode
While the default way of building the SQL conditions uses an `IN()` list
(as shown above), this approach will not work well for a high number of flags,
as the value list for `IN()` grows.
For MySQL, depending on your MySQL settings, this can even hit the
`max_allowed_packet` limit with the generated query, or the similar query length maximum for PostgreSQL.
In this case, consider changing the flag query mode to `:bit_operator`
instead of `:in_list`, like so:
```ruby
has_flags 1 => :warpdrive,
2 => :shields,
:flag_query_mode => :bit_operator
```
This will modify the generated condition and named_scope methods to use bit
operators in the SQL instead of an `IN()` list:
```ruby
Spaceship.warpdrive_condition # "(spaceships.flags & 1 = 1)",
Spaceship.not_warpdrive_condition # "(spaceships.flags & 1 = 0)",
Spaceship.shields_condition # "(spaceships.flags & 2 = 2)",
Spaceship.not_shields_condition # "(spaceships.flags & 2 = 0)",
Spaceship.warpdrive # :conditions => "(spaceships.flags & 1 = 1)"
Spaceship.not_warpdrive # :conditions => "(spaceships.flags & 1 = 0)"
Spaceship.shields # :conditions => "(spaceships.flags & 2 = 2)"
Spaceship.not_shields # :conditions => "(spaceships.flags & 2 = 0)"
```
The drawback is that due to the [bitwise operation][bitwise_operation] being done on the SQL side,
this query can not use an index on the flags column.
### Updating flag column by raw sql
If you need to do mass updates without initializing object for each row, you can
use `#set_flag_sql` method on your class. Example:
```ruby
Spaceship.set_flag_sql(:warpdrive, true) # "flags = flags | 1"
Spaceship.set_flag_sql(:shields, false) # "flags = flags & ~2"
```
And then use it in:
```ruby
Spaceship.update_all Spaceship.set_flag_sql(:shields, false)
```
Beware that using multiple flag manipulation sql statements in the same query
probably will not have the desired effect (at least on sqlite3, not tested
on other databases), so you *should not* do this:
```ruby
Spaceship.update_all "#{Spaceship.set_flag_sql(:shields, false)},#{
Spaceship.set_flag_sql(:warpdrive, true)}"
```
General rule of thumb: issue only one flag update per update statement.
### Skipping flag column check
By default when you call has_flags in your code it will automatically check
your database to see if you have correct column defined.
Sometimes this may not be a wanted behaviour (e.g. when loading model without
database connection established) so you can set `:check_for_column` option to
false to avoid it.
```ruby
has_flags 1 => :warpdrive,
2 => :shields,
:check_for_column => false
```
## Running the gem tests
WARNING: You may want to read [bin/test.bash](https://github.com/pboling/flag_shih_tzu/blob/master/bin/test.bash) first.
Running the test script will switch rubies, create gemsets, install gems, and get a lil' crazy with the hips.
Just:
$ rake test:all
This will internally use rvm and bundler to load specific Rubies and ActiveRecord versions
before executing the tests (see `gemfiles/`), e.g.:
$ NOCOVER=true BUNDLE_GEMFILE='gemfiles/Gemfile.activerecord-4.1.x' bundle exec rake test
All tests will use an in-memory sqlite database by default.
If you want to use a different database, see `test/database.yml`,
install the required adapter gem and use the DB environment variable to
specify which config from `test/database.yml` to use, e.g.:
$ NOCOVER=true DB=mysql bundle exec rake
You will also need to create, and configure access to, the test databases for any adapters you want to test, e.g. mysql:
mysql> CREATE USER 'foss'@'localhost';
Query OK, 0 rows affected (0.00 sec)
mysql> GRANT ALL PRIVILEGES ON *.* TO 'foss'@'localhost';
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE DATABASE flag_shih_tzu_test;
Query OK, 1 row affected (0.00 sec)
## Authors
[Peter Boling](http://github.com/pboling),
[Patryk Peszko](http://github.com/ppeszko),
[Sebastian Roebke](http://github.com/boosty),
[David Anderson](http://github.com/alpinegizmo),
[Tim Payton](http://github.com/dizzy42)
and a helpful group of
[contributors](https://github.com/pboling/flag_shih_tzu/contributors).
Thanks!
Find out more about Peter Boling's work
[RailsBling.com](http://railsbling.com/).
Find out more about XING
[Devblog](http://devblog.xing.com/).
## How you can help!
Take a look at the `reek` list, which is the file called `REEK`, and stat fixing things. Once you complete a change, run the tests. See "Running the gem tests".
If the tests pass refresh the `reek` list:
bundle exec rake reek > REEK
Follow the instructions for "Contributing" below.
## Contributing
1. Fork it
2. Create your feature branch (`git checkout -b my-new-feature`)
3. Commit your changes (`git commit -am 'Added some feature'`)
4. Push to the branch (`git push origin my-new-feature`)
5. Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
6. Create new Pull Request
## Versioning
This library aims to adhere to [Semantic Versioning 2.0.0](http://semver.org/).
Violations of this scheme should be reported as bugs. Specifically,
if a minor or patch version is released that breaks backward
compatibility, a new version should be immediately released that
restores compatibility. Breaking changes to the public API will
only be introduced with new major versions.
As a result of this policy, you can (and should) specify a
dependency on this gem using the [Pessimistic Version Constraint](http://docs.rubygems.org/read/chapter/16#page74) with two digits of precision.
For example:
```ruby
spec.add_dependency 'flag_shih_tzu', '~> 0.0'
```
## 2012 Change of Ownership and 0.3.X Release Notes
FlagShihTzu was originally a [XING AG](http://www.xing.com/) project. [Peter Boling](http://peterboling.com) was a long time contributor and watcher of the project.
In September 2012 XING transferred ownership of the project to Peter Boling. Peter Boling had been maintaining a
fork with extended capabilities. These additional features become a part of the 0.3 line. The 0.2 line of the gem will
remain true to XING's original. The 0.3 line aims to maintain complete parity and compatibility with XING's original as
well. I will continue to monitor other forks for original ideas and improvements. Pull requests are welcome, but please
rebase your work onto the current master to make integration easier.
More information on the changes for 0.3.X: [pboling/flag_shih_tzu/wiki/Changes-for-0.3.x](https://github.com/pboling/flag_shih_tzu/wiki/Changes-for-0.3.x)
## Alternatives
I discovered in October 2015 that Michael Grosser had created a competing tool, `bitfields`, way back in 2010, exactly a year after this tool was created. It was a very surreal moment, as I had thought this was the only game in town and it was when I began using and hacking on it. Once I got over that moment I became excited, because competition makes things better, right? So, now I am looking forward to a shootout some lazy Saturday. Until then there's this: http://www.railsbling.com/posts/why-use-flag_shih_tzu/
There is little that `bitfields` does better. The code is [less efficient](https://github.com/grosser/bitfields/blob/master/lib/bitfields.rb#L186 "recalculating and throwing away much of the result in many places"), albeit more readable, not as well tested, has almost zero inline documentation, and simply can't do many of the things I've built into `flag_shih_tzu`. If you are still on legacy Ruby or legacy Rails, or using jRuby, then use `flag_shih_tzu`. If you need multiple flag columns on a single model, use `flag_shih_tzu`.
Will there ever be a merb/rails-like love fest between the projects? It would be interesting. I like his name better. I like my features better. I like some of his code better, and some of my code better. I've been wanting to do a full re-write of `flag_shih_tzu` ever since I inherited the project from [XING](https://github.com/xing), but I haven't had time. So I don't know.
## License
MIT License
Copyright (c) 2011 [XING AG](http://www.xing.com/)
Copyright (c) 2012 - 2018 [Peter Boling][peterboling] of [RailsBling.com][railsbling]
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.
[semver]: http://semver.org/
[pvc]: http://docs.rubygems.org/read/chapter/16#page74
[railsbling]: http://www.railsbling.com
[peterboling]: http://www.peterboling.com
[documentation]: http://rdoc.info/github/pboling/flag_shih_tzu/frames
[homepage]: https://github.com/pboling/flag_shih_tzu
[bit_field]: http://en.wikipedia.org/wiki/Bit_field
[bitwise_operation]: http://en.wikipedia.org/wiki/Bitwise_operation