// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef GARNET_BIN_HWSTRESS_UTIL_H_
#define GARNET_BIN_HWSTRESS_UTIL_H_

#include <lib/zx/time.h>

#include <random>
#include <string>
#include <vector>

namespace hwstress {

// Convert double representing a number of seconds to a zx::duration.
zx::duration SecsToDuration(double secs);

// Convert zx::duration to double representing the number of seconds.
double DurationToSecs(zx::duration d);

// Represent a double as a hexadecimal constant.
std::string DoubleAsHex(double v);

// Create a 64-bit pattern by repeating the same 8-bit value 8 times.
inline uint64_t RepeatByte(uint8_t v) { return v * 0x0101'0101'0101'0101ul; }

// Round up the given value |n| so that it is a multiple of |k|.
inline uint64_t RoundUp(uint64_t n, uint64_t k) { return ((n + (k - 1)) / k) * k; }

// Round down the given value |n| so that it is a multiple of |k|.
inline uint64_t RoundDown(uint64_t n, uint64_t k) { return (n / k) * k; }

// Functions to simplify constants.
inline constexpr uint64_t kiB(uint64_t n) { return n * 1024ul; }
inline constexpr uint64_t MiB(uint64_t n) { return n * 1024ul * 1024ul; }
inline constexpr uint64_t GiB(uint64_t n) { return n * 1024ul * 1024ul * 1024ul; }

// Knuth's MMIX LCE parameters. [1]
//
// This random number engine produces 64-bit output, and is roughly
// 4 times faster than std::mt19937_64 (or any other 64-bit generator
// in the C++ standard library), while still maintaining reasonable
// quality output.
//
// [1] D. E. Knuth, The Art of Computer Programming – Seminumerical
//     Algorithms, 3rd Edition, Vol. 2, Pearson Education, 2000.
using knuth_mmix_rng =
    std::linear_congruential_engine<uint64_t, 6364136223846793005, 1442695040888963407, 0>;
using fast_64bit_rng = knuth_mmix_rng;

}  // namespace hwstress

#endif  // GARNET_BIN_HWSTRESS_UTIL_H_