大量错误地在Javascript中舍入 [英] Large numbers erroneously rounded in Javascript
问题描述
请参阅以下代码：
< html>
< head>
< script src =http://www.json.org/json2.jstype =text / javascript>< / script>
< script type =text / javascript>
var jsonString ='{id：714341252076979033，type：FUZZY}';
var jsonParsed = JSON.parse（jsonString）;
console.log（jsonString，jsonParsed）;
< / script>
< / head>
< body>
< / body>
< / html>
当我在Firefox 3.5中看到我的控制台时，jsonParsed的值为：
Object id = 714341252076979100 type = FUZZY
即数字是四舍五入的。尝试不同的价值观，相同的结果（数字四舍五入）。
我也没有得到它的舍入规则。 714341252076979136四舍五入到714341252076979200，而714341252076979135四舍五入到714341252076979100。编辑：看到下面的第一条评论。显然这不是关于JSON，而是关于Javascript数字处理。但是问题仍然存在：
为什么会发生这种情况？
你在这里看到的实际上是两个圆角的影响。 ECMAScript中的数字在内部表示为双精度浮点数。当 id 设置为 714341252076979033 （ 0x9e9d9958274c359 ，它实际上被分配了最接近的可表示的双精度值，即 714341252076979072 （ 0x9e9d9958274c380 ）。当你打印出这个值时，它被四舍五入为十五位十进制数字，它给出 14341252076979100 。
See this code:
<html>
<head>
<script src="http://www.json.org/json2.js" type="text/javascript"></script>
<script type="text/javascript">
var jsonString = '{"id":714341252076979033,"type":"FUZZY"}';
var jsonParsed = JSON.parse(jsonString);
console.log(jsonString, jsonParsed);
</script>
</head>
<body>
</body>
</html>
When I see my console in Firefox 3.5, the value of jsonParsed is:
Object id=714341252076979100 type=FUZZY
I.e the number is rounded. Tried different values, the same outcome (number rounded).
I also don't get its rounding rules. 714341252076979136 is rounded to 714341252076979200, whereas 714341252076979135 is rounded to 714341252076979100.
EDIT: see first comment below. Apparently this is not about JSON, but something about Javascript number handling. But the question remains:
Why is this happening?
What you're seeing here is actually the effect of two roundings. Numbers in ECMAScript are internally represented double-precision floating-point. When id is set to 714341252076979033 (0x9e9d9958274c359 in hex), it actually is assigned the nearest representable double-precision value, which is 714341252076979072 (0x9e9d9958274c380). When you print out the value, it is being rounded to 15 significant decimal digits, which gives 14341252076979100.
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