[{"_1":2,"_3":-5,"_4":-5},"loaderData",{"_5":6,"_7":8},"actionData","errors","root",{"_11":-5},"routes/user.$name.collections",{"_9":10,"_11":12,"_13":14,"_15":16,"_17":18,"_19":16},"topics",[35],"user",{"_20":21,"_13":14,"_22":23,"_24":25,"_26":27,"_28":29,"_30":31,"_32":31,"_33":34},"loginname","zhongguozhe","page",1,"limit",20,"total","id","27241","avatar_url","https://avatars1.githubusercontent.com/u/24197448?v=4","githubUsername","zhanghengxin","create_at","2017-03-02 07:19:40.723","score",30,"topic_count",3,"reply_count","is_star",false,{"_20":36,"_37":38,"_39":40,"_41":42,"_43":44,"_45":46,"_47":34,"_48":34,"_32":49,"_50":51,"_26":52,"_53":54},"37062","author_id","26625","tab","share","content","在一次代码优化的过程中把\r\n```js\r\n// a,b都为正整数且大于0\r\nwhile (a>=b) {\r\n a-=b;\r\n}\r\n```\r\n优化为\r\n```js\r\n// a,b都为正整数且大于0\r\nwhile (a>=b) {\r\n let tmpB = b;\r\n while (a>=tmpB) {\r\n let tmpShiftB = tmpB<<1;\r\n if (a>=tmpShiftB) {\r\n tmpB = tmpShiftB;\r\n } else {\r\n a-=tmpB;\r\n }\r\n }\r\n}\r\n```\r\n本意是如果a很大，b很小的情况，也能把快速进行减法运算。\r\n但后来发现a一旦很大，就会死循环，这个还是概率出现。\r\n后来debug发现到一定时候tmpShiftB会变成0，导致死循环。\r\n当时就想肯定是位移符的坑，后来发现有下面问题\r\n```\r\ntmpShiftB到达2147483648后左移一位变0\r\n```\r\n我一看乐了，这不是2的32次方嘛，肯定是JS当有符号的int32型算了，然后溢出了，八成是谷歌引擎的的BUG！\r\n但想想别高兴的太早，看看标准怎么说，毕竟制定标准的人也贼坑。让我们看看标准怎么写的。\r\n\r\n[ecma-262的第9版左位移说明](http://www.ecma-international.org/ecma-262/9.0/index.html#sec-left-shift-operator)：\r\n\r\n```\r\n12.9.3The Left Shift Operator ( << )\r\nNOTE\r\nPerforms a bitwise left shift operation on the left operand by the amount specified by the right operand.\r\n\r\n12.9.3.1Runtime Semantics: Evaluation\r\nShiftExpression:ShiftExpression<