N random numbers with constant sum

randomSumArray.js

// https://stackoverflow.com/a/26976623/1597964
function randomSumArray(len, sum, d) {
	var _sum = 0;
	var arr = [];
	var n, i;

	if (!d && d !== 0) {
		d = 100;
	}

	for (i = 0; i < len; i++) {
		var from = (100 - d) * 1000,
			to = (100 + d) * 1000,
			n = Math.floor(Math.random() * (to - from + 1) + from); //random integer between from..to

		_sum += n;
		arr.push(n);
	}

	var x = sum / _sum;

	_sum = 0; //count sum (again)
	for (var i = 0; i < len; i++) {
		arr[i] = Math.round(arr[i] * x);
		_sum += arr[i];
	}

	var diff = sum - _sum;

	// Correct the array if its sum does not match required sum (usually by a small bit)
	if (diff) {
		x = diff / Math.abs(diff); //x will be 1 or -1
		var j = 0;
		while (diff && j < 1000) { //limit to a finite number of 'corrections'
			i = Math.floor(Math.random() * (len + 1)); //random index in the array
			if (arr[i] + x >= 0) {
				arr[i] += x;
				diff -= x;
			}
			j++;
		}
	}

	return arr;
}