如何在JavaScript算术运算中检测数字上溢/下溢？ [英] How to detect numeric overflow/underflow in JavaScript arithmetic operations?

问题描述

我今天正在进行编码测试，目标是在JavaScript中添加2个字符串整数表示时捕获所有边缘情况。我无法得到的一个案例是如何检测存储在IEEE 754数字中的总和的上溢/下溢。

I was doing a coding test today, the goal was to catch all edge cases when adding 2 integer representations of strings in JavaScript. One case I could not get was how to detect overflow/underflow for the sum stored in the IEEE 754 numeric.

通常，在C中，我会查看数字的二进制表示，但在JavaScript中，我只能查看32位的整数值。

Normally, in C, I'd look at the binary representation of the numeric, but in JavaScript, I can only look at 32 bits worth of the integer value.

这是我的代码：

function string_add(a, b) {
    if (arguments.length !== 2)
        throw new Error('two arguments expected as input');

    // ensure we have strings
    if (typeof a !== 'string' || typeof b !== 'string')
        throw new Error('bad parameter types');

    // ensure we do not have empty strings
    if (a.length === 0 || b.length === 0)
        throw new Error('an empty string is an invalid argument');

    // ensure we have integer arguments
    if (0 !== (+a % 1) || 0 !== (+b % 1))
        throw new Error('expected numeric integer strings for arguments');

    var sum = +a + +b;      // create numeric sum of a and b.
    sum+='';                // convert numeric sum to string
    return sum;
}

提前致谢。

推荐答案

实际上，由于浮点数学运算的方式，Javascript中的整数是53位信息。

Actually, integers in Javascript are 53 bits of information due to the way floating point math works.

最后一次我需要做类似的事情......

The last time I needed to do something similar I did...

var MAX_INT = Math.pow(2, 53);
var MIN_INT = -MAX_INT;

var value = MAX_INT * 5;
if (value >= MAX_INT) {
  alert("Overflow");
}

// Note. you have to use MAX_INT itself as the overflow mark because of this:
value = MAX_INT+1;
if (value > MAX_INT) {
  alert("Overflow test failed");
}

编辑在考虑之后，它会是更容易说：

EDIT After thinking about it, it would be easier to say:

var MAX_INT = Math.pow(2, 53) -1;
var MIN_INT = -MAX_INT;

因为那是你知道的最大的INT没有溢出。

since that is the largest INT that you know hasn't overflowed.

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