HashUtils.h

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// Copyright (c) 2002-present, OpenMS Inc. -- EKU Tuebingen, ETH Zurich, and FU Berlin
// SPDX-License-Identifier: BSD-3-Clause
//
// --------------------------------------------------------------------------
// $Maintainer: OpenMS Team $
// $Authors: OpenMS Team $
// --------------------------------------------------------------------------
 
#pragma once
 
#include <cstddef>
#include <cstdint>
#include <functional>
#include <string>
#include <type_traits>
 
namespace OpenMS
{
  inline std::size_t fnv1a_hash_bytes(const void* data, std::size_t size) noexcept
  {
    const auto* bytes = static_cast<const unsigned char*>(data);
    // FNV-1a 64-bit constants
    std::size_t hash = 14695981039346656037ull; // FNV offset basis
    for (std::size_t i = 0; i < size; ++i)
    {
      hash ^= bytes[i];
      hash *= 1099511628211ull; // FNV prime
    }
    return hash;
  }
 
  inline std::size_t fnv1a_hash_string(const std::string& s) noexcept
  {
    return fnv1a_hash_bytes(s.data(), s.size());
  }
 
  inline void hash_combine(std::size_t& seed, std::size_t value) noexcept
  {
    seed ^= value + 0x9e3779b97f4a7c15 + (seed << 6) + (seed >> 2);
  }
 
  template<typename T>
  inline std::size_t hash_int(T value) noexcept
  {
    static_assert(std::is_integral_v<T>, "hash_int requires an integral type");
    return fnv1a_hash_bytes(&value, sizeof(T));
  }
 
  inline std::size_t hash_char(char c) noexcept
  {
    // Apply FNV-1a algorithm for single character
    std::size_t hash = 14695981039346656037ull;
    hash ^= static_cast<unsigned char>(c);
    hash *= 1099511628211ull;
    return hash;
  }
 
  template<typename T>
  inline std::size_t hash_float(T value) noexcept
  {
    static_assert(std::is_floating_point_v<T>, "hash_float requires a floating point type");
    // Normalize -0.0 to +0.0 (they compare equal but have different bit patterns)
    if (value == T(0)) value = T(0);
    return fnv1a_hash_bytes(&value, sizeof(T));
  }
 
} // namespace OpenMS