//===- subzero/src/IceRNG.h - Random number generator -----------*- C++ -*-===//
//
//                        The Subzero Code Generator
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file declares a random number generator.
//
//===----------------------------------------------------------------------===//

#ifndef SUBZERO_SRC_ICERNG_H
#define SUBZERO_SRC_ICERNG_H

#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Compiler.h"
#include <cstdint>

namespace Ice {

class RandomNumberGenerator {
  RandomNumberGenerator() = delete;
  RandomNumberGenerator(const RandomNumberGenerator &) = delete;
  RandomNumberGenerator &operator=(const RandomNumberGenerator &) = delete;

public:
  explicit RandomNumberGenerator(uint64_t Seed, llvm::StringRef Salt = "");
  uint64_t next(uint64_t Max);

private:
  uint64_t State;
};

// This class adds additional random number generator utilities. The
// reason for the wrapper class is that we want to keep the
// RandomNumberGenerator interface identical to LLVM's.
class RandomNumberGeneratorWrapper {
  RandomNumberGeneratorWrapper() = delete;
  RandomNumberGeneratorWrapper(const RandomNumberGeneratorWrapper &) = delete;
  RandomNumberGeneratorWrapper &
  operator=(const RandomNumberGeneratorWrapper &) = delete;

public:
  uint64_t operator()(uint64_t Max) { return RNG.next(Max); }
  bool getTrueWithProbability(float Probability);
  explicit RandomNumberGeneratorWrapper(RandomNumberGenerator &RNG)
      : RNG(RNG) {}

private:
  RandomNumberGenerator &RNG;
};

// RandomShuffle is an implementation of std::random_shuffle() that
// doesn't change across stdlib implementations.  Adapted from a
// sample implementation at cppreference.com.
template <class RandomIt, class RandomFunc>
void RandomShuffle(RandomIt First, RandomIt Last, RandomFunc &&RNG) {
  for (auto i = Last - First - 1; i > 0; --i)
    std::swap(First[i], First[RNG(i + 1)]);
}

} // end of namespace Ice

#endif // SUBZERO_SRC_ICERNG_H