bf.rb

def make_jump_table(prog)
  pc = 0
  jump_table = {}
  stack = []
  while pc < prog.size
    case prog[pc]
    when ?[
      stack.push pc
    when ?]
      raise '対応する[がない' if stack.empty?
      start = stack.pop
      jump_table[start] = pc
    end
    pc+=1
  end

  raise '対応するい]がない' unless stack.empty?

  jump_table
end


buf=Array.new(100, 0)
ptr=0
prog=File.read(ARGV.first)
pc=0
jump_table = make_jump_table(prog)
stack = []
while pc < prog.size
  ch = prog[pc]
  case ch
  when ?>
    ptr+=1
    pc+=1
  when ?<
    ptr-=1
    pc+=1
  when ?+
    buf[ptr] += 1
    pc+=1
  when ?-
    buf[ptr] -= 1
    pc+=1
  when ?.
    print [buf[ptr]].pack('c')
    pc+=1
  when ?,
    # fall through
    pc+=1
  when ?[
    if buf[ptr]==0
      pc = jump_table[pc] + 1
    else
      stack.push pc
      pc+=1
    end
  when ?]
    pc = stack.pop
  when ?\n,' '
      pc+=1
  else
    raise "Invalid char: #{ch}."
  end
end