ip算法 位移

function ip(str) {
  var length = str.length;
  var ans = 0;
  var stack = [];
  var step = 0;
  var lastStep = 0;
  var lastchar = ''

  // 处理每一次位移
  function handle() {
    if (stack.length === 0) {
      if (lastchar === 'b') {
        ans = ans | (1 << (32 - step - 1));
      } 
      step++;
    } else {
      var nStep = 0;
      stack.forEach(function(item, index) {
        nStep += item * Math.pow(10, (stack.length - 1 - index))
      });
      
      if (lastchar === 'b') {
        ans = ans | ((Math.pow(2, nStep) - 1) <<  (32 - step - nStep))
      }
      step += nStep;
    }
  }

  for (var i = 0; i < length; i++) {
    // 每次处理一次变更
    if (str[i] === 'a' || str[i] === 'b') {
      lastchar = str[i];
      handle();
      stack = [];
    } else {
      stack.push(Number(str[i]));
    }
  }
  var a = ans >> 24;
  var b = (ans >> 16) & (Math.pow(2, 8) - 1);
  var c = (ans >> 8) & (Math.pow(2, 8) - 1);
  var d = ans & (Math.pow(2, 8) - 1);
  if (a === -1) {
    a = 255;
  }
  return a + '.' + b + '.' + c + '.' + d;
}

var ans = ip('7ab7ab7a2b6ab');
console.log(ans);
console.log(ans === '1.1.1.129');

var ans = ip('32a');
console.log(ans);

var ans = ip('32b');
console.log(ans);

var ans = ip('8b8a8b8a');
console.log(ans);

var ans = ip('a7b8a8a7ab');
console.log(ans);
var ans = ip('aa6baa6baa6b8a');
console.log(ans);