Why this simple way to generate random integers work

var r = 12345

func rand() int {
    r = r*1103515245 + 12345
    return r & 0x7fffffff
}

This go function generate random numbers but I do not why it works (I did not evaluate how well it works.. just eyeballing the results). Can someone explain please? Thanks

you could see it here in action: https://go.dev/play/p/ji4-avVV1Mn

I am aware this may not be cryptographically safe.