How to detect numeric overflow/underflow in JavaScript arithmetic operations?

2024/2/27 7:13:13

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.

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.

Here's the code I had:

function string_add(a, b) {if (arguments.length !== 2)throw new Error('two arguments expected as input');// ensure we have stringsif (typeof a !== 'string' || typeof b !== 'string')throw new Error('bad parameter types');// ensure we do not have empty stringsif (a.length === 0 || b.length === 0)throw new Error('an empty string is an invalid argument');// ensure we have integer argumentsif (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 stringreturn sum;

Thanks in advance.


Edit: JavaScript now has a Number.MAX_SAFE_INTEGER

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

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");

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

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

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

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