// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#ifndef RUNTIME_VM_RANDOM_H_
#define RUNTIME_VM_RANDOM_H_

#include <atomic>

#include "vm/allocation.h"
#include "vm/flags.h"
#include "vm/globals.h"

namespace dart {

DECLARE_FLAG(uint64_t, random_seed);

class Random {
 public:
  Random();
  // Seed must be non-zero.
  explicit Random(uint64_t seed);
  ~Random();

  uint32_t NextUInt32();
  uint64_t NextUInt64() {
    return (static_cast<uint64_t>(NextUInt32()) << 32) |
           static_cast<uint64_t>(NextUInt32());
  }

  // Returns a random number that's a valid JS integer.
  //
  // All IDs that can be returned over the service protocol should be
  // representable as JS integers and should be generated using this method.
  //
  // See https://github.com/dart-lang/sdk/issues/53081.
  uint64_t NextJSInt() {
    // Number.MAX_SAFE_INTEGER (2 ^ 53 - 1)
    const uint64_t kMaxJsInt = 0x1FFFFFFFFFFFFF;
    return NextUInt64() & kMaxJsInt;
  }

  static uint64_t GlobalNextUInt64();
  static void Init();
  static void Cleanup();

  // Generates a uniform random variable in the range [0,1].
  double NextDouble();

 private:
  uint64_t NextState();
  void Initialize(uint64_t seed);

  std::atomic<uint64_t> _state;

  DISALLOW_COPY_AND_ASSIGN(Random);
};

}  // namespace dart

#endif  // RUNTIME_VM_RANDOM_H_