Class: Koota::VM

Inherits:
Object
  • Object
show all
Defined in:
lib/koota/vm.rb

Overview

Implements a Koota virtual machine.

Defined Under Namespace

Modules: Opcodes

Constant Summary collapse

CALL_STACK_MAX = 
256

Instance Method Summary collapse

Constructor Details

#initialize(random: Random.new) ⇒ VM

Returns a new instance of VM.



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# File 'lib/koota/vm.rb', line 20

def initialize(random: Random.new)
  @random = random
end

Instance Method Details

#call(memory) ⇒ Object 



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# File 'lib/koota/vm.rb', line 24

def call(memory)
  output = ''.dup
  call_stack = []
  offset = 0

  while offset < memory.length
    op = memory[offset]
    offset += 1

    case op
    when Opcodes::HALT then break
    when Opcodes::JUMP
      offset = Decode.short(memory, offset)

    when Opcodes::PUT
      decoded, advance = Decode.utf8(memory, offset)
      output << decoded
      offset += advance

    when Opcodes::PICK
      list_pointer = Decode.short(memory, offset)
      list_length  = Decode.short(memory, list_pointer)

      # Jump to the chosen offset.
      # Multiply the rand by two because each offset has two bytes, and the
      # list length represents the length of each two-byte block.
      # Also, the offset starts at 1 to skip the list length.
      offset = Decode.short(memory, list_pointer + 2 * @random.rand(1..list_length))

    when Opcodes::CALL
      break if call_stack.length >= CALL_STACK_MAX

      routine_pointer = Decode.short(memory, offset)
      call_stack.push(offset + 2) # opcode after the routine pointer
      offset = routine_pointer

    when Opcodes::RET
      offset = call_stack.pop
      break if offset.nil?

    when Opcodes::JRND
      offset = @random.rand(2) == 1 ? Decode.short(memory, offset) : offset + 2

    else break
    end
  end

  output
end