hash32.h

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// === hash32.h ========================================================================================================
//                                               Sen Infrastructure
//                   Released under the Apache License v2.0 (SPDX-License-Identifier Apache-2.0).
//                                    See the LICENSE.txt file for more information.
//                   © Airbus SAS, Airbus Helicopters, and Airbus Defence and Space SAU/GmbH/SAS.
// =====================================================================================================================
 
#ifndef SEN_CORE_BASE_HASH32_H
#define SEN_CORE_BASE_HASH32_H
 
#include "sen/core/base/compiler_macros.h"
#include "sen/core/base/numbers.h"
#include "sen/core/base/result.h"
 
// std
#include <array>
#include <cstdint>
#include <cstring>
#include <filesystem>
#include <memory>
#include <numeric>
#include <string>
#include <string_view>

 
namespace sen
{


constexpr u32 hashSeed = 23835769U;
constexpr u32 propertyHashSeed = 19830715U;
constexpr u32 methodHashSeed = 93580253U;
constexpr u32 eventHashSeed = 12125807U;

constexpr u32 nonPresentTypeHash = 18121997U;

template <typename InputIterator>
[[nodiscard]] u32 crc32(InputIterator first, InputIterator last) noexcept;

[[nodiscard]] inline u32 crc32(std::string_view str) noexcept { return crc32(str.begin(), str.end()); }

template <typename... Types>
[[nodiscard]] u32 hashCombine(u32 seed, const Types&... args) noexcept;

template <typename... Types>
[[nodiscard]] uint_fast32_t platformDependentHashCombine(uint_fast32_t seed, const Types&... args) noexcept;

[[nodiscard]] std::unique_ptr<unsigned char[]> decompressSymbol(const void* compressedData);

[[nodiscard]] std::string decompressSymbolToString(const void* compressedData, unsigned int originalSize);

[[nodiscard]] Result<void, std::string> fileToCompressedArray(const std::filesystem::path& inputFile,
                                                              std::string_view symbolName,
                                                              const std::filesystem::path& outputFile);

// [[nodiscard]] leads: the macro expands to a GNU attribute on gcc and clang, and a standard
// attribute list has to start the declaration.
[[nodiscard]] SEN_DEPRECATED_FOR(0.7.0, fileToCompressedArray) bool fileToCompressedArrayFile(
  const std::filesystem::path& inputFile,
  std::string_view symbolName,
  const std::filesystem::path& outputFile);

 
//----------------------------------------------------------------------------------------------------------------------
// Inline implementation
//----------------------------------------------------------------------------------------------------------------------
 
namespace impl
{
 
// FN-1a implementation of the hash
constexpr u32 fnv1aOffsetBasis = 0x811c9dc5;
constexpr u32 fnv1aPrime = 0x01000193;

template <typename T>
inline constexpr std::enable_if_t<std::is_integral_v<T>, u32> hashIntegral(T value) noexcept
{
  using UT = std::make_unsigned_t<T>;
  auto u = static_cast<UT>(value);
 
  auto hash = fnv1aOffsetBasis;
 
  // process from most-significant byte to least-significant
  for (int i = (sizeof(UT) - 1) * 8; i >= 0; i -= 8)
  {
    hash ^= static_cast<u8>((u >> i) & 0xFF);  // NOLINT
    hash *= fnv1aPrime;
  }
 
  return hash;
}

template <typename T>
inline constexpr std::enable_if_t<std::is_floating_point_v<T>, u32> hashFloat(T value) noexcept
{
  using IntType = std::conditional_t<sizeof(T) == 4, u32, u64>;
 
  IntType bits = 0;
  std::memcpy(&bits, &value, sizeof(T));
  return hashIntegral(bits);
}
 
template <typename T, typename Enable = void>
struct hash;
 
template <typename T>
struct hash<T, typename std::enable_if_t<std::is_integral_v<T>>>
{
  inline u32 operator()(T value) const noexcept { return hashIntegral(value); }
};
 
template <typename T>
struct hash<T, typename std::enable_if_t<std::is_floating_point_v<T>>>
{
  inline u32 operator()(T value) const noexcept { return hashFloat(value); }
};
 
template <>
struct hash<bool>
{
  inline u32 operator()(bool value) const noexcept { return hashIntegral(static_cast<u8>(value)); }
};
 
template <>
struct hash<i8>
{
  inline u32 operator()(i8 value) const noexcept { return hashIntegral(static_cast<u8>(value)); }
};
 
template <>
struct hash<std::basic_string_view<char>>
{
  inline u32 operator()(const std::basic_string_view<char>& value) const noexcept
  {
    auto hash = fnv1aOffsetBasis;
 
    for (unsigned char c: value)
    {
      hash ^= c;
      hash *= fnv1aPrime;
    }
 
    return hash;
  }
};
 
template <>
struct hash<std::basic_string<char>>
{
  inline u32 operator()(const std::basic_string<char>& value) const noexcept
  {
    return hash<std::basic_string_view<char>>()(value);
  }
};
 
template <typename T>
struct hash<T, std::enable_if_t<std::is_enum_v<T>>>
{
  inline u32 operator()(T value) const noexcept { return hashIntegral(static_cast<std::underlying_type_t<T>>(value)); }
};
 
template <typename T>
struct hash<T*>
{
  u32 operator()(T* value) const noexcept
  {
    return hashIntegral(reinterpret_cast<std::uintptr_t>(value));  // NOLINT
  }
};
 
[[nodiscard]] std::array<u32, 256> generateCrc32LookupTable() noexcept;  // NOLINT
 
template <typename T>
inline void hashCombineImpl(u32& seed, const T& val) noexcept
{
  seed ^= hash<T>()(val) + 0x9e3779b9U + (seed << 6) + (seed >> 2);  // NOLINT
}
 
template <typename T>
inline void platformDependentHashCombineImpl(std::uint_fast32_t& seed, const T& val) noexcept
{
  seed ^= std::hash<T>()(val) + 0x9e3779b9U + (seed << 6) + (seed >> 2);  // NOLINT
}
 
}  // namespace impl
 
template <typename InputIterator>
inline u32 crc32(InputIterator first, InputIterator last) noexcept
{
  // generate lookup table only on first use then cache it - this is thread-safe.
  static auto const table = impl::generateCrc32LookupTable();
 
  // calculate the checksum - make sure to clip to 32 bits, for systems that don't
  // have a true (fast) 32-bit type.
  return u32 {0xffffffffUL} &  // NOLINT
         ~std::accumulate(first,
                          last,
                          ~u32 {0} & u32 {0xffffffffUL},  // NOLINT
                          [](u32 checksum, u32 value)
                          { return table[(checksum ^ value) & 0xffU] ^ (checksum >> 8U); });  // NOLINT
}
 
template <typename... Types>
inline u32 hashCombine(u32 seed, const Types&... args) noexcept
{
  (impl::hashCombineImpl(seed, args), ...);
  return seed;
}
 
template <typename... Types>
inline std::uint_fast32_t platformDependentHashCombine(std::uint_fast32_t seed, const Types&... args) noexcept
{
  (impl::platformDependentHashCombineImpl(seed, args), ...);
  return seed;
}
 
}  // namespace sen
 
#endif  // SEN_CORE_BASE_HASH32_H