text: var mapping = {
    0: {
      0: 0
    , 90: -90
    , 180: -180
    , 270: 90
    }
  , 90: {
      0: 90
    , 90: 0
    , 180: -90
    , 270: 180
    }
  , 180: {
      0: 180
    , 90: 90
    , 180: 0
    , 270: -90
    }
  , 270: {
      0: -90
    , 90: -180
    , 180: 90
    , 270: 0
    }
  }
  
  module.exports = function rotator(oldRotation, newRotation) {
    var r1 = oldRotation < 0 ? 360 + oldRotation % 360 : oldRotation % 360
      , r2 = newRotation < 0 ? 360 + newRotation % 360 : newRotation % 360
  
    return mapping[r1][r2]
  }
  