if loc2.screen_pos then
    return Text.previous_screen_lineA(State, loc2)
  else
    return Text.previous_screen_lineB(State, loc2)
  end
end
function Text.previous_screen_lineA(State, loc2)

function Text.previous_screen_lineB(State, loc2)
  if loc2.screen_lineB > 1 then
    return {line=loc2.line, screen_lineB=loc2.screen_line-1, screen_posB=1}
  else
    -- switch to A side
    return {line=loc2.line, screen_line=#State.line_cache[loc2.line].screen_line_starting_pos, screen_pos=1}
  end
end