YAKL_random.h

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#pragma once
// Included by YAKL.h
 
__YAKL_NAMESPACE_WRAPPER_BEGIN__
namespace yakl {
 
  // Simple, low-overhead random numbers
  // https://burtleburtle.net/bob/rand/smallprng.html
 
  class Random {
  protected:
    typedef unsigned long long u8;
    u8 static constexpr rot(u8 x, u8 k) { return (((x)<<(k))|((x)>>(64-(k)))); }
    struct State { u8 a, b, c, d; };
    State state;
 
  public:
 
    YAKL_INLINE Random()                            { set_seed(1368976481L); } // I made up this number
    YAKL_INLINE Random(u8 seed)                     { set_seed(seed); }
    YAKL_INLINE Random(Random const            &in) { this->state = in.state; }
    YAKL_INLINE Random(Random                 &&in) { this->state = in.state; }
    YAKL_INLINE Random &operator=(Random const &in) { this->state = in.state; return *this; }
    YAKL_INLINE Random &operator=(Random      &&in) { this->state = in.state; return *this; }
 
    YAKL_INLINE void set_seed(u8 seed) {
      state.a = 0xf1ea5eed;  state.b = seed;  state.c = seed;  state.d = seed;
      for (int i=0; i<20; ++i) { gen(); }
    }
 
    YAKL_INLINE u8 gen() {
      u8 e    = state.a - rot(state.b, 7);
      state.a = state.b ^ rot(state.c,13);
      state.b = state.c + rot(state.d,37);
      state.c = state.d + e;
      state.d = e       + state.a;
      return state.d;
    }
 
    template <class T> YAKL_INLINE T genFP() {
      return static_cast<T>(gen()) / static_cast<T>(std::numeric_limits<u8>::max());
    }
 
    template <class T> YAKL_INLINE T genFP(T lb, T ub) {
      return genFP<T>() * (ub-lb) + lb;
    }
 
  };
 
}
__YAKL_NAMESPACE_WRAPPER_END__