require_relative 'assembler'

module Asm
  module Arm
    
  # Relocation constants
  # Note that in this assembler, a relocation simply means any
  # reference to a label that can only be determined at assembly time
  # or later (as in the normal meaning)
  
  R_ARM_PC24 = 0x01
  R_ARM_ABS32 = 0x02
  
  # Unofficial (cant be used for extern relocations)
  R_ARM_PC12 = 0xF0
  
  # TODO actually find the closest somehow
  def self.closest_addrtable(as)
    as.objects.find do |obj|
      obj.is_a?(Asm::ARM::AddrTableObject)
    end || (raise Asm::AssemblyError.new('could not find addrtable to use', nil))
  end

  def self.write_resolved_relocation(io, addr, type)
    case type
    when R_ARM_PC24
      diff = addr - io.tell - 8
      packed = [diff >> 2].pack('l')
      io << packed[0,3]
    when R_ARM_ABS32
      packed = [addr].pack('l')
      io << packed
    when R_ARM_PC12
      diff = addr - io.tell - 8
      if (diff.abs > 2047)
        raise Asm::AssemblyError.new('offset too large for R_ARM_PC12 relocation',
                                    nil)
      end
      
      val = diff.abs
      sign = (diff>0)?1:0
      
      curr = io.read_uint32
      io.seek(-4, IO::SEEK_CUR)
      
      io.write_uint32 (curr & ~0b00000000100000000000111111111111) | 
                      val | (sign << 23)
    else
      raise 'unknown relocation type'
    end
  end

end