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ircd: Allow configurable prime on the bernstein hasher.

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This commit is contained in:
Jason Volk 2017-11-06 12:20:30 -08:00
parent 688ff545d6
commit f7ee7ea211
1 changed files with 19 additions and 13 deletions
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32
include/ircd/hash.h
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@ -28,15 +28,16 @@
namespace ircd
{
// constexpr bernstein string hasher suite; these functions will hash the
// string at compile time leaving an integer residue at runtime.
constexpr size_t hash(const char *const &str, const size_t i = 0);
constexpr size_t hash(const char16_t *const &str, const size_t i = 0);
constexpr size_t hash(const std::string_view &str, const size_t i = 0);
// string at compile time leaving an integer residue at runtime. Decent
// primes are at least 7681 and 5381.
template<size_t PRIME = 7681> constexpr size_t hash(const char *const &str, const size_t i = 0);
template<size_t PRIME = 7681> constexpr size_t hash(const char16_t *const &str, const size_t i = 0);
template<size_t PRIME = 7681> constexpr size_t hash(const std::string_view &str, const size_t i = 0);
// Note that at runtime this hash uses multiplication on every character
// which can consume many cycles...
size_t hash(const std::string &str, const size_t i = 0);
size_t hash(const std::u16string &str, const size_t i = 0);
template<size_t PRIME = 7681> size_t hash(const std::string &str, const size_t i = 0);
template<size_t PRIME = 7681> size_t hash(const std::u16string &str, const size_t i = 0);
/// ircd:: reserves the $ character over a string as an alias for hash()
template<class string>
@ -150,41 +151,46 @@ const
}
/// Runtime hashing of a std::u16string (for js). Non-cryptographic.
inline size_t
template<size_t PRIME>
size_t
ircd::hash(const std::u16string &str,
const size_t i)
{
return i >= str.size()? 7681ULL : (hash(str, i+1) * 33ULL) ^ str.at(i);
return i >= str.size()? PRIME : (hash(str, i+1) * 33ULL) ^ str.at(i);
}
/// Runtime hashing of a std::string. Non-cryptographic.
inline size_t
template<size_t PRIME>
size_t
ircd::hash(const std::string &str,
const size_t i)
{
return i >= str.size()? 7681ULL : (hash(str, i+1) * 33ULL) ^ str.at(i);
return i >= str.size()? PRIME : (hash(str, i+1) * 33ULL) ^ str.at(i);
}
/// Runtime hashing of a string_view. Non-cryptographic.
template<size_t PRIME>
constexpr size_t
ircd::hash(const std::string_view &str,
const size_t i)
{
return i >= str.size()? 7681ULL : (hash(str, i+1) * 33ULL) ^ str.at(i);
return i >= str.size()? PRIME : (hash(str, i+1) * 33ULL) ^ str.at(i);
}
/// Compile-time hashing of a wider string literal (for js). Non-cryptographic.
template<size_t PRIME>
constexpr size_t
ircd::hash(const char16_t *const &str,
const size_t i)
{
return !str[i]? 7681ULL : (hash(str, i+1) * 33ULL) ^ str[i];
return !str[i]? PRIME : (hash(str, i+1) * 33ULL) ^ str[i];
}
/// Compile-time hashing of a string literal. Non-cryptographic.
template<size_t PRIME>
constexpr size_t
ircd::hash(const char *const &str,
const size_t i)
{
return !str[i]? 7681ULL : (hash(str, i+1) * 33ULL) ^ str[i];
return !str[i]? PRIME : (hash(str, i+1) * 33ULL) ^ str[i];
}