ffi-bitfield
Bit field for Ruby-FFI
Installation
gem install ffi-bitfieldUsage
Classes
- class BitStruct < FFI::Struct
- class ManagedBitStruct < FFI::ManagedStruct
Loading
require 'ffi/bit_struct'
require 'ffi/managed_bit_struct'Define your struct
class Struct1 < FFI::BitStruct
layout \
:a, :uint8,
:b, :uint8
bit_fields :a,
:u, 2,
:v, 2,
:w, 1,
:x, 1,
:y, 1,
:z, 1
endReading
s = Struct1.new
s[:a] = 63
p s[:u] # 3
p s[:v] # 3
p s[:w] # 1
p s[:x] # 1
p s[:y] # 0
p s[:z] # 0Writing
s = Struct1.new
s[:u] = 0
s[:v] = 0
s[:w] = 0
s[:x] = 0
s[:y] = 1
p s[:a] # 64Typed Bit Fields
You can use the bit_fields_typed method to define bit fields with type information. This method accepts a hash where keys are field names and values are arrays containing [width, type]. For boolean fields (width of 1 with :bool type), it automatically generates a ? helper method:
class AccessFlags < FFI::BitStruct
layout \
:flags, :uint8
bit_fields_typed :flags,
revoked: [1, :bool], # Creates revoked and revoked? methods
expired: [1, :bool], # Creates expired and expired? methods
some_string: [4, :string], # Creates some_string method (no ? helper)
reserved: [2, :int] # Creates reserved method (no ? helper)
end
flags = AccessFlags.new
flags[:revoked] = 1
flags[:expired] = 0
p flags.revoked? # => true
p flags.expired? # => false
flags[:expired] = 1
p flags.expired? # => trueThe ? methods are only generated for fields that are 1 bit wide and have type :bool. Other field types can be used for documentation purposes and future functionality.
Inspecting Bit Fields
You can use the bit_field_members method to get a hash of bit fields grouped by parent field:
class Flags < FFI::BitStruct
layout \
:value, :uint8
bit_fields :value,
:read, 1,
:write, 1,
:execute, 1,
:unused, 5
end
p Flags.bit_field_members
# => {:value=>[:read, :write, :execute, :unused]}For more detailed information, you can use the bit_field_layout method:
p Flags.bit_field_layout
# => {
# :value => {
# :read => { :start => 0, :width => 1 },
# :write => { :start => 1, :width => 1 },
# :execute => { :start => 2, :width => 1 },
# :unused => { :start => 3, :width => 5 }
# }
# }These methods are useful for custom pretty printing or introspection of your bit struct classes.
Loading
require 'ffi/bit_field'The above is the same as below.
require 'ffi/bit_struct'
require 'ffi/managed_bit_struct'Development
git clone https://github.com/kojix2/ffi-bitfield
cd ffi-bitfield
bundle install
bundle exec rake test
Contributing
Your feedback is important.
ffi-bitfield is a library under development, so even small improvements like typofix are welcome! Please feel free to send us your pull requests. Bug reports and pull requests are welcome on GitHub at https://github.com/kojix2/ffi-bitfield.
Do you need commit rights to my repository?
Do you want to get admin rights and take over the project?
If so, please feel free to contact me @kojix2.
License
The gem is available as open source under the terms of the MIT License.