aten/src/ATen/native/utils/ParamsHash.h

#pragma once

#include <memory>
#include <mutex>

namespace at { namespace native {

// Hashing machinery for Params
// Fowler–Noll–Vo hash function
// see https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
template <typename Params>
struct ParamsHash {
  // Params must be a POD because we read out its memory
  // contenst as char* when hashing
  static_assert(std::is_pod<Params>::value, "Params is not POD");

  size_t operator()(const Params& params) const {
    auto ptr = reinterpret_cast<const uint8_t*>(&params);
    uint32_t value = 0x811C9DC5;
    for (const auto i : c10::irange((int)sizeof(Params))) {
      value ^= ptr[i];
      value *= 0x01000193;
    }
    return (size_t)value;
  }
};

template <typename Params>
struct ParamsEqual {
  // Params must be a POD because we read out its memory
  // contenst as char* when comparing
  static_assert(std::is_pod<Params>::value, "Params is not POD");

  bool operator()(const Params& a, const Params& b) const {
    auto ptr1 = reinterpret_cast<const uint8_t*>(&a);
    auto ptr2 = reinterpret_cast<const uint8_t*>(&b);
    return memcmp(ptr1, ptr2, sizeof(Params)) == 0;
  }
};


}}  // at::native