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Clean a hash function definition

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* spot/misc/hashfunc.hh: make the definition of FNV hash magic constants
  more generic
This commit is contained in:
Maximilien Colange 2018-03-07 17:21:50 +01:00
parent 85bc05e737
commit 304f5623d8
1 changed files with 15 additions and 10 deletions
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25
spot/misc/hashfunc.hh
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@ -23,7 +23,7 @@
#pragma once #pragma once
#include <cstddef> #include <cstddef>
#include <cstdint> #include <type_traits>
namespace spot namespace spot
{ {
@ -64,25 +64,30 @@ namespace spot
return (key >> 3) * 2654435761U; return (key >> 3) * 2654435761U;
} }
/// Struct for Fowler-Noll-Vo parameters /// Struct for Fowler-Noll-Vo parameters
template<class T> template<class T, class Enable = void>
struct fnv struct fnv
{}; {};
/// Fowler-Noll-Vo hash parameters for 32 bits /// Fowler-Noll-Vo hash parameters for 32 bits
template<> template<class T>
struct fnv<uint32_t> struct fnv<T, typename std::enable_if<sizeof(T) == 4>::type>
{ {
static constexpr uint32_t init = 2166136261UL; static_assert(std::is_integral<T>::value && std::is_unsigned<T>::value,
static constexpr uint32_t prime = 16777619UL; "Fowler-Noll-Vo hash requires an unsigned integral type");
static constexpr T init = 2166136261UL;
static constexpr T prime = 16777619UL;
}; };
/// Fowler-Noll-Vo hash parameters for 64 bits /// Fowler-Noll-Vo hash parameters for 64 bits
template<> template<class T>
struct fnv<uint64_t> struct fnv<T, typename std::enable_if<sizeof(T) == 8>::type>
{ {
static constexpr uint64_t init = 14695981039346656037UL; static_assert(std::is_integral<T>::value && std::is_unsigned<T>::value,
static constexpr uint64_t prime = 1099511628211UL; "Fowler-Noll-Vo hash requires an unsigned integral type");
static constexpr T init = 14695981039346656037ULL;
static constexpr T prime = 1099511628211ULL;
}; };
/// \brief Fowler-Noll-Vo hash function /// \brief Fowler-Noll-Vo hash function