forked from bitcoin/bitcoin
-
Notifications
You must be signed in to change notification settings - Fork 1.2k
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Implement std::unordered_map/set compatible hasher classes for salted…
… hashes Allows convenient salted hashing with unordered maps and sets. Useful when there is a risk of unbalanced hash buckets slowing things down, e.g. when externally supplied hashes are used as keys into a map.
- Loading branch information
Showing
3 changed files
with
89 additions
and
0 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,12 @@ | ||
// Copyright (c) 2019 The Dash Core developers | ||
// Distributed under the MIT software license, see the accompanying | ||
// file COPYING or http://www.opensource.org/licenses/mit-license.php. | ||
|
||
#include "saltedhasher.h" | ||
#include "random.h" | ||
|
||
#include <limits> | ||
|
||
SaltedHasherBase::SaltedHasherBase() : k0(GetRand(std::numeric_limits<uint64_t>::max())), k1(GetRand(std::numeric_limits<uint64_t>::max())) {} | ||
|
||
SaltedHasherBase StaticSaltedHasher::s; |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,75 @@ | ||
// Copyright (c) 2019 The Dash Core developers | ||
// Distributed under the MIT software license, see the accompanying | ||
// file COPYING or http://www.opensource.org/licenses/mit-license.php. | ||
|
||
#ifndef SALTEDHASHER_H | ||
#define SALTEDHASHER_H | ||
|
||
#include "hash.h" | ||
#include "uint256.h" | ||
|
||
/** Helper classes for std::unordered_map and std::unordered_set hashing */ | ||
|
||
template<typename T> struct SaltedHasherImpl; | ||
|
||
template<typename N> | ||
struct SaltedHasherImpl<std::pair<uint256, N>> | ||
{ | ||
static std::size_t CalcHash(const std::pair<uint256, N>& v, uint64_t k0, uint64_t k1) | ||
{ | ||
return SipHashUint256Extra(k0, k1, v.first, (uint32_t) v.second); | ||
} | ||
}; | ||
|
||
template<typename N> | ||
struct SaltedHasherImpl<std::pair<N, uint256>> | ||
{ | ||
static std::size_t CalcHash(const std::pair<N, uint256>& v, uint64_t k0, uint64_t k1) | ||
{ | ||
return SipHashUint256Extra(k0, k1, v.second, (uint32_t) v.first); | ||
} | ||
}; | ||
|
||
template<> | ||
struct SaltedHasherImpl<uint256> | ||
{ | ||
static std::size_t CalcHash(const uint256& v, uint64_t k0, uint64_t k1) | ||
{ | ||
return SipHashUint256(k0, k1, v); | ||
} | ||
}; | ||
|
||
struct SaltedHasherBase | ||
{ | ||
/** Salt */ | ||
const uint64_t k0, k1; | ||
|
||
SaltedHasherBase(); | ||
}; | ||
|
||
/* Allows each instance of unordered maps/sest to have their own salt */ | ||
template<typename T, typename S> | ||
struct SaltedHasher | ||
{ | ||
S s; | ||
std::size_t operator()(const T& v) const | ||
{ | ||
return SaltedHasherImpl<T>::CalcHash(v, s.k0, s.k1); | ||
} | ||
}; | ||
|
||
/* Allows to use a static salt for all instances. The salt is a random value set at startup | ||
* (through static initialization) | ||
*/ | ||
struct StaticSaltedHasher | ||
{ | ||
static SaltedHasherBase s; | ||
|
||
template<typename T> | ||
std::size_t operator()(const T& v) const | ||
{ | ||
return SaltedHasherImpl<T>::CalcHash(v, s.k0, s.k1); | ||
} | ||
}; | ||
|
||
#endif//SALTEDHASHER_H |