def mandelbrot(c_r, c_i)
  limit=95
  iterations=0
  cr = (c_r * 100).to_i
  ci = (c_i * 100).to_i
  zr = zi = 0
  # Avoid sqrt by squaring the threshold: sqrt(x) < 1000 => x < 1000000
  while iterations<limit
    zr2 = zr*zr
    zi2 = zi*zi
    break if zr2+zi2 >= 1000000
    zr, zi = (zr2-zi2)/100+cr, (zr*zi*2)/100+ci
    iterations+=1
  end
  return iterations
end

def mandel_calc(min_r, min_i, max_r, max_i, res)
  cur_i = min_i
  while cur_i > max_i
    putc "|"
    cur_r = min_r
    while cur_r < max_r
      ch = 127 - mandelbrot(cur_r, cur_i)
      putc ch  # Use putc with integer - no string allocation!
      cur_r += res
    end
    putc "|"
    putc "\n"
    cur_i -= res
  end
end

mandel_calc(-2, 1, 1, -1, 0.04)