See https://gist.github.com/odanado/26834f30406b25c47a5b and https://gist.github.com/oupo/eb53ffcd1db2020b3f20

calcInverse.js

function calcPow(a, n, mask) {
    return n === 0 ? 1 :
        Math.imul((n & 1 ? a : 1), calcPow(Math.imul(a, a) & mask, n >>> 1, mask));
}

function calcInverse(mul, mask) {
    return calcPow(mul, mask >>> 1, mask);
}

function u32(x) {
    return x >>> 0;
}

function main() {
    var mul = 0x41c64e6d;
    var incr = 0x6073;
    var mask = 0x7FFFFFFF;

    var inverseMul = calcInverse(mul, mask);
    var inverseIncr = ~Math.imul(inverseMul, incr) + 1;

    console.log("%s, %s", u32(inverseMul).toString(16), u32(inverseIncr).toString(16));
}

main();

• mul = 0x41c64e6d, incr = 0x6073のとき

$ node calcInverse.js
eeb9eb65, a3561a1

• mul = 0x6c078965, incr = 0x1のとき

$ node calcInverse.js
1638806d, e9c77f93