特殊的简单随机数发生器

How to create a function, which on every call generates a random integer number? This number must be most random as possible (according to uniform distribution). It is only allowed to use one static variable and at most 3 elementary steps, where each step consists of only one basic arithmetic operation of arity 1 or 2.

示例:

int myrandom(void){
  static int x;
  x = some_step1;
  x = some_step2;
  x = some_step3;
  return x;
}

基本算术运算有+、-、%、and、not、xor、or、左移、右移、乘除.当然，不允许使用 rand()、random() 或类似的东西.

int seed = 123456789;

int rand()
{
  seed = (a * seed + c) % m;
  return seed;
}