Class: BitStruct::SignedField

Inherits:
Field
  • Object
show all
Defined in:
lib/bit-struct/signed-field.rb

Overview

Class for signed integers in network order, 1-16 bits, or 8n bits. Declared with BitStruct.signed.

Instance Attribute Summary

Attributes inherited from Field

#default, #display_name, #format, #length, #name, #offset, #options

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Field

#class_name, default, #describe, #initialize, #inspect_in_object, #inspectable?

Constructor Details

This class inherits a constructor from BitStruct::Field

Class Method Details

.class_name ⇒ Object

Used in describe.



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# File 'lib/bit-struct/signed-field.rb', line 6

def self.class_name
  @class_name ||= "signed"
end

Instance Method Details

#add_accessors_to(cl, attr = name) ⇒ Object

:nodoc:



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# File 'lib/bit-struct/signed-field.rb', line 10

def add_accessors_to(cl, attr = name) # :nodoc:
  offset_byte = offset / 8
  offset_bit = offset % 8
  
  length_bit = offset_bit + length
  length_byte = (length_bit/8.0).ceil
  last_byte = offset_byte + length_byte - 1
  max = 2**length-1
  mid = 2**(length-1)
  max_unsigned = 2**length
  to_signed = proc {|n| (n>=mid) ? n - max_unsigned : n}
#      to_signed = proc {|n| (n>=mid) ? -((n ^ max) + 1) : n}
  
  divisor = options[:fixed] || options["fixed"]
  divisor_f = divisor && divisor.to_f
#      if divisor and not divisor.is_a? Fixnum
#        raise ArgumentError, "fixed-point divisor must be a fixnum"
#      end

  endian = (options[:endian] || options["endian"]).to_s
  case endian
  when "native"
    ctl = length_byte <= 2 ? "s" : "l"
    if length == 16 or length == 32
      to_signed = proc {|n| n}
      # with pack support, to_signed can be replaced with no-op
    end
  when "little"
    ctl = length_byte <= 2 ? "v" : "V"
  when "network", "big", ""
    ctl = length_byte <= 2 ? "n" : "N"
  else
    raise ArgumentError,
      "Unrecognized endian option: #{endian.inspect}"
  end
  
  data_is_big_endian =
    ([1234].pack(ctl) == [1234].pack(length_byte <= 2 ? "n" : "N"))
  
  if length_byte == 1
    rest = 8 - length_bit
    mask  = ["0"*offset_bit + "1"*length + "0"*rest].pack("B8")[0].ord
    mask2 = ["1"*offset_bit + "0"*length + "1"*rest].pack("B8")[0].ord
    
    cl.class_eval do
      if divisor
        define_method attr do ||
          to_signed[(self[offset_byte] & mask) >> rest] / divisor_f
        end

        define_method "#{attr}=" do |val|
          val = (val * divisor).round
          self[offset_byte] =
            (self[offset_byte] & mask2) | ((val<<rest) & mask)
        end

      else
        define_method attr do ||
          to_signed[(self[offset_byte] & mask) >> rest]
        end

        define_method "#{attr}=" do |val|
          self[offset_byte] =
            (self[offset_byte] & mask2) | ((val<<rest) & mask)
        end
      end
    end
  
  elsif offset_bit == 0 and length % 8 == 0
    field_length = length
    byte_range = offset_byte..last_byte
    
    cl.class_eval do
      case field_length
      when 8
        if divisor
          define_method attr do ||
            to_signed[self[offset_byte]] / divisor_f
          end

          define_method "#{attr}=" do |val|
            val = (val * divisor).round
            self[offset_byte] = val
          end
      
        else
          define_method attr do ||
            to_signed[self[offset_byte]]
          end

          define_method "#{attr}=" do |val|
            self[offset_byte] = val
          end
        end
    
      when 16, 32
        if divisor
          define_method attr do ||
            to_signed[self[byte_range].unpack(ctl).first] / divisor_f
          end

          define_method "#{attr}=" do |val|
            val = (val * divisor).round
            self[byte_range] = [val].pack(ctl)
          end
        
        else
          define_method attr do ||
            to_signed[self[byte_range].unpack(ctl).first]
          end

          define_method "#{attr}=" do |val|
            self[byte_range] = [val].pack(ctl)
          end
        end
      
      else
        reader_helper = proc do |substr|
          bytes = substr.unpack("C*")
          bytes.reverse! unless data_is_big_endian
          bytes.inject do |sum, byte|
            (sum << 8) + byte
          end
        end
        
        writer_helper = proc do |val|
          bytes = []
          val += max_unsigned if val < 0
          while val > 0
            bytes.push val % 256
            val = val >> 8
          end
          if bytes.length < length_byte
            bytes.concat [0] * (length_byte - bytes.length)
          end

          bytes.reverse! if data_is_big_endian
          bytes.pack("C*")
        end
        
        if divisor
          define_method attr do ||
            to_signed[reader_helper[self[byte_range]] / divisor_f]
          end
          
          define_method "#{attr}=" do |val|
            self[byte_range] = writer_helper[(val * divisor).round]
          end
        
        else
          define_method attr do ||
            to_signed[reader_helper[self[byte_range]]]
          end
          
          define_method "#{attr}=" do |val|
            self[byte_range] = writer_helper[val]
          end
        end
      end
    end

  elsif length_byte == 2 # unaligned field that fits within two whole bytes
    byte_range = offset_byte..last_byte
    rest = 16 - length_bit
    
    mask  = ["0"*offset_bit + "1"*length + "0"*rest]
    mask = mask.pack("B16").unpack(ctl).first
    
    mask2 = ["1"*offset_bit + "0"*length + "1"*rest]
    mask2 = mask2.pack("B16").unpack(ctl).first

    cl.class_eval do
      if divisor
        define_method attr do ||
          to_signed[(self[byte_range].unpack(ctl).first & mask) >> rest] /
             divisor_f
        end

        define_method "#{attr}=" do |val|
          val = (val * divisor).round
          x = (self[byte_range].unpack(ctl).first & mask2) |
            ((val<<rest) & mask)
          self[byte_range] = [x].pack(ctl)
        end

      else
        define_method attr do ||
          to_signed[(self[byte_range].unpack(ctl).first & mask) >> rest]
        end

        define_method "#{attr}=" do |val|
          x = (self[byte_range].unpack(ctl).first & mask2) |
            ((val<<rest) & mask)
          self[byte_range] = [x].pack(ctl)
        end
      end
    end
  
  elsif length_byte == 3 # unaligned field that fits within 3 whole bytes
    byte_range = offset_byte..last_byte
    rest = 32 - length_bit
    
    mask  = ["0"*offset_bit + "1"*length + "0"*rest]
    mask = mask.pack("B32").unpack(ctl).first
    
    mask2 = ["1"*offset_bit + "0"*length + "1"*rest]
    mask2 = mask2.pack("B32").unpack(ctl).first

    cl.class_eval do
      if divisor
        define_method attr do ||
          bytes = self[byte_range]
          bytes << 0
          to_signed[((bytes.unpack(ctl).first & mask) >> rest)] /
             divisor_f
        end

        define_method "#{attr}=" do |val|
          val = (val * divisor).round
          bytes = self[byte_range]
          bytes << 0
          x = (bytes.unpack(ctl).first & mask2) |
            ((val<<rest) & mask)
          self[byte_range] = [x].pack(ctl)[0..2]
        end

      else
        define_method attr do ||
          bytes = self[byte_range]
          bytes << 0
          to_signed[(bytes.unpack(ctl).first & mask) >> rest]
        end

        define_method "#{attr}=" do |val|
          bytes = self[byte_range]
          bytes << 0
          x = (bytes.unpack(ctl).first & mask2) |
            ((val<<rest) & mask)
          self[byte_range] = [x].pack(ctl)[0..2]
        end
      end
    end
  
  else
    raise "unsupported: #{inspect}"
  end
end