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|
require 'thread'
require 'bindata/base_primitive'
module BinData
# Defines a number of classes that contain a bit based integer.
# The integer is defined by endian and number of bits.
module BitField #:nodoc: all
@@mutex = Mutex.new
class << self
def define_class(name, nbits, endian, signed = :unsigned)
@@mutex.synchronize do
unless BinData.const_defined?(name)
new_class = Class.new(BinData::BasePrimitive)
BitField.define_methods(new_class, nbits, endian.to_sym, signed.to_sym)
RegisteredClasses.register(name, new_class)
BinData.const_set(name, new_class)
end
end
BinData.const_get(name)
end
def define_methods(bit_class, nbits, endian, signed)
bit_class.module_eval <<-END
#{create_params_code(nbits)}
def assign(val)
#{create_nbits_code(nbits)}
#{create_clamp_code(nbits, signed)}
super(val)
end
def do_write(io)
#{create_nbits_code(nbits)}
val = _value
#{create_int2uint_code(nbits, signed)}
io.writebits(val, #{nbits}, :#{endian})
end
def do_num_bytes
#{create_nbits_code(nbits)}
#{create_do_num_bytes_code(nbits)}
end
def bit_aligned?
true
end
#---------------
private
def read_and_return_value(io)
#{create_nbits_code(nbits)}
val = io.readbits(#{nbits}, :#{endian})
#{create_uint2int_code(nbits, signed)}
val
end
def sensible_default
0
end
END
end
def create_params_code(nbits)
if nbits == :nbits
"mandatory_parameter :nbits"
else
""
end
end
def create_nbits_code(nbits)
if nbits == :nbits
"nbits = eval_parameter(:nbits)"
else
""
end
end
def create_do_num_bytes_code(nbits)
if nbits == :nbits
"nbits / 8.0"
else
nbits / 8.0
end
end
def create_clamp_code(nbits, signed)
if nbits == :nbits
create_dynamic_clamp_code(signed)
else
create_fixed_clamp_code(nbits, signed)
end
end
def create_dynamic_clamp_code(signed)
if signed == :signed
max = "(1 << (nbits - 1)) - 1"
min = "-((#{max}) + 1)"
else
max = "(1 << nbits) - 1"
min = "0"
end
"val = val.clamp(#{min}, #{max})"
end
def create_fixed_clamp_code(nbits, signed)
if nbits == 1 && signed == :signed
raise "signed bitfield must have more than one bit"
end
if signed == :signed
max = "(1 << (#{nbits} - 1)) - 1"
min = "-((#{max}) + 1)"
else
min = "0"
max = "(1 << #{nbits}) - 1"
end
clamp = "(val = val.clamp(#{min}, #{max}))"
if nbits == 1
# allow single bits to be used as booleans
clamp = "(val == true) ? 1 : (not val) ? 0 : #{clamp}"
end
"val = #{clamp}"
end
def create_int2uint_code(nbits, signed)
if signed != :signed
""
elsif nbits == :nbits
"val &= (1 << nbits) - 1"
else
"val &= #{(1 << nbits) - 1}"
end
end
def create_uint2int_code(nbits, signed)
if signed != :signed
""
elsif nbits == :nbits
"val -= (1 << nbits) if (val >= (1 << (nbits - 1)))"
else
"val -= #{1 << nbits} if (val >= #{1 << (nbits - 1)})"
end
end
end
end
# Create classes for dynamic bitfields
{
"Bit" => :big,
"BitLe" => :little,
"Sbit" => [:big, :signed],
"SbitLe" => [:little, :signed],
}.each_pair { |name, args| BitField.define_class(name, :nbits, *args) }
# Create classes on demand
module BitFieldFactory
def const_missing(name)
mappings = {
/^Bit(\d+)$/ => :big,
/^Bit(\d+)le$/ => :little,
/^Sbit(\d+)$/ => [:big, :signed],
/^Sbit(\d+)le$/ => [:little, :signed]
}
mappings.each_pair do |regex, args|
if regex =~ name.to_s
nbits = $1.to_i
return BitField.define_class(name, nbits, *args)
end
end
super(name)
end
end
BinData.extend BitFieldFactory
end
|
