common/include/common_defs.hpp

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

#ifndef _COMMON_DEFS_HPP_
#define _COMMON_DEFS_HPP_

#include <cstdint>
#include <string>
#include <memory>
#include <iostream>
#include <random>
#include <chrono>
#include <thread>

/// DataSketches namespace
namespace datasketches {

static const uint64_t DEFAULT_SEED = 9001;

enum resize_factor { X1 = 0, X2, X4, X8 };

template<typename A> using string = std::basic_string<char, std::char_traits<char>, typename std::allocator_traits<A>::template rebind_alloc<char>>;

// common random declarations
namespace random_utils {
  static std::random_device rd; // possibly unsafe in MinGW with GCC < 9.2
  static thread_local std::mt19937_64 rand(rd());
  static thread_local std::uniform_real_distribution<> next_double(0.0, 1.0);
  static thread_local std::uniform_int_distribution<uint64_t> next_uint64(0, UINT64_MAX);

  // thread-safe random bit
  static thread_local std::independent_bits_engine<std::mt19937, 1, uint32_t>
    random_bit(static_cast<uint32_t>(std::chrono::system_clock::now().time_since_epoch().count()
      + std::hash<std::thread::id>{}(std::this_thread::get_id())));

  inline void override_seed(uint64_t s) {
    rand.seed(s);
  }
}

// utility function to hide unused compiler warning
// usually has no additional cost
template<typename T> void unused(T&&...) {}

// common helping functions
// TODO: find a better place for them

constexpr uint8_t log2(uint32_t n) {
  return (n > 1) ? 1 + log2(n >> 1) : 0;
}

constexpr uint8_t lg_size_from_count(uint32_t n, double load_factor) {
  return log2(n) + ((n > static_cast<uint32_t>((1 << (log2(n) + 1)) * load_factor)) ? 2 : 1);
}

// stream helpers to hide casts
template<typename T>
static inline T read(std::istream& is) {
  T value;
  is.read(reinterpret_cast<char*>(&value), sizeof(T));
  return value;
}

template<typename T>
static inline void read(std::istream& is, T* ptr, size_t size_bytes) {
  is.read(reinterpret_cast<char*>(ptr), size_bytes);
}

template<typename T>
static inline void write(std::ostream& os, T value) {
  os.write(reinterpret_cast<const char*>(&value), sizeof(T));
}

template<typename T>
static inline void write(std::ostream& os, const T* ptr, size_t size_bytes) {
  os.write(reinterpret_cast<const char*>(ptr), size_bytes);
}

template<typename T>
T byteswap(T value) {
  char* ptr = static_cast<char*>(static_cast<void*>(&value));
  const int len = sizeof(T);
  for (size_t i = 0; i < len / 2; ++i) {
    std::swap(ptr[i], ptr[len - i - 1]);
  }
  return value;
}

template<typename T>
static inline T read_big_endian(std::istream& is) {
  T value;
  is.read(reinterpret_cast<char*>(&value), sizeof(T));
  return byteswap(value);
}

// wrapper for iterators to implement operator-> returning temporary value
template<typename T>
class return_value_holder {
public:
  return_value_holder(T value): value_(value) {}
  const T* operator->() const { return std::addressof(value_); }
private:
  T value_;
};

} // namespace

#endif // _COMMON_DEFS_HPP_