IP とサブネットマスクから範囲を計算（IPv4 のみ）

calc_ip.js

var PATTERN = /^(\d|[01]?\d\d|2[0-4]\d|25[0-5])\.(\d|[01]?\d\d|2[0-4]\d|25[0-5])\.(\d|[01]?\d\d|2[0-4]\d|25[0-5])\.(\d|[01]?\d\d|2[0-4]\d|25[0-5])\/(\d|[012]?\d|3[0-2])?$/;
var BIT_STR = "11111111111111111111111111111111";
var MIN_BIT = 8;
var MAX_BIT = 30;

function calcIp(ip)
{
    var result = [];
    var ip = ip.match(PATTERN);

    if (ip) {
        ip[5] = ip[5] < MIN_BIT ? MIN_BIT
              : MAX_BIT < ip[5] ? MAX_BIT : ip[5];

        var total = ip[1] << 24 | ip[2] << 16 | ip[3] << 8 | ip[4];
        var bit   = BIT_STR.length - ip[5];
        var mask  = [
            parseInt(BIT_STR.substring(bit  ), 2) << bit,
            parseInt(BIT_STR.substring(ip[5]), 2)
        ];
        var rst  = [
            total & mask[0],
            total | mask[1]
        ];

        var min = [
            255 & rst[0] >> 24,
            255 & rst[0] >> 16,
            255 & rst[0] >>  8,
            255 & rst[0],
        ];

        var max = [
            255 & rst[1] >> 24,
            255 & rst[1] >> 16,
            255 & rst[1] >>  8,
            255 & rst[1],
        ];

        result = [ min, max,
            [ min[0], min[1], min[2], min[3] + 1 ],
            [ max[0], max[1], max[2], max[3] - 1 ]
        ];
    }
    return result;
}