Use SipHash-2-4 for CCoinsCache index

This is ~1.7x slower than the Lookup3-of-Xor-with-salt construct we were
using before, but it is a primitive designed for exactly this.
This commit is contained in:
Pieter Wuille 2016-05-06 20:47:12 +02:00
parent 0b1295b066
commit 382c871d28
4 changed files with 13 additions and 76 deletions

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@ -56,7 +56,11 @@ void CCoinsViewBacked::SetBackend(CCoinsView &viewIn) { base = &viewIn; }
bool CCoinsViewBacked::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return base->BatchWrite(mapCoins, hashBlock); }
CCoinsViewCursor *CCoinsViewBacked::Cursor() const { return base->Cursor(); }
CCoinsKeyHasher::CCoinsKeyHasher() : salt(GetRandHash()) {}
SaltedTxidHasher::SaltedTxidHasher()
{
GetRandBytes((unsigned char*)&k0, sizeof(k0));
GetRandBytes((unsigned char*)&k1, sizeof(k1));
}
CCoinsViewCache::CCoinsViewCache(CCoinsView *baseIn) : CCoinsViewBacked(baseIn), hasModifier(false), cachedCoinsUsage(0) { }

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@ -8,6 +8,7 @@
#include "compressor.h"
#include "core_memusage.h"
#include "hash.h"
#include "memusage.h"
#include "serialize.h"
#include "uint256.h"
@ -264,21 +265,22 @@ public:
}
};
class CCoinsKeyHasher
class SaltedTxidHasher
{
private:
uint256 salt;
/** Salt */
uint64_t k0, k1;
public:
CCoinsKeyHasher();
SaltedTxidHasher();
/**
* This *must* return size_t. With Boost 1.46 on 32-bit systems the
* unordered_map will behave unpredictably if the custom hasher returns a
* uint64_t, resulting in failures when syncing the chain (#4634).
*/
size_t operator()(const uint256& key) const {
return key.GetHash(salt);
size_t operator()(const uint256& txid) const {
return SipHashUint256(k0, k1, txid);
}
};
@ -295,7 +297,7 @@ struct CCoinsCacheEntry
CCoinsCacheEntry() : coins(), flags(0) {}
};
typedef boost::unordered_map<uint256, CCoinsCacheEntry, CCoinsKeyHasher> CCoinsMap;
typedef boost::unordered_map<uint256, CCoinsCacheEntry, SaltedTxidHasher> CCoinsMap;
/** Cursor for iterating over CoinsView state */
class CCoinsViewCursor

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@ -80,67 +80,3 @@ template std::string base_blob<256>::GetHex() const;
template std::string base_blob<256>::ToString() const;
template void base_blob<256>::SetHex(const char*);
template void base_blob<256>::SetHex(const std::string&);
static void inline HashMix(uint32_t& a, uint32_t& b, uint32_t& c)
{
// Taken from lookup3, by Bob Jenkins.
a -= c;
a ^= ((c << 4) | (c >> 28));
c += b;
b -= a;
b ^= ((a << 6) | (a >> 26));
a += c;
c -= b;
c ^= ((b << 8) | (b >> 24));
b += a;
a -= c;
a ^= ((c << 16) | (c >> 16));
c += b;
b -= a;
b ^= ((a << 19) | (a >> 13));
a += c;
c -= b;
c ^= ((b << 4) | (b >> 28));
b += a;
}
static void inline HashFinal(uint32_t& a, uint32_t& b, uint32_t& c)
{
// Taken from lookup3, by Bob Jenkins.
c ^= b;
c -= ((b << 14) | (b >> 18));
a ^= c;
a -= ((c << 11) | (c >> 21));
b ^= a;
b -= ((a << 25) | (a >> 7));
c ^= b;
c -= ((b << 16) | (b >> 16));
a ^= c;
a -= ((c << 4) | (c >> 28));
b ^= a;
b -= ((a << 14) | (a >> 18));
c ^= b;
c -= ((b << 24) | (b >> 8));
}
uint64_t uint256::GetHash(const uint256& salt) const
{
uint32_t a, b, c;
const uint32_t *pn = (const uint32_t*)data;
const uint32_t *salt_pn = (const uint32_t*)salt.data;
a = b = c = 0xdeadbeef + WIDTH;
a += pn[0] ^ salt_pn[0];
b += pn[1] ^ salt_pn[1];
c += pn[2] ^ salt_pn[2];
HashMix(a, b, c);
a += pn[3] ^ salt_pn[3];
b += pn[4] ^ salt_pn[4];
c += pn[5] ^ salt_pn[5];
HashMix(a, b, c);
a += pn[6] ^ salt_pn[6];
b += pn[7] ^ salt_pn[7];
HashFinal(a, b, c);
return ((((uint64_t)b) << 32) | c);
}

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@ -140,11 +140,6 @@ public:
{
return ReadLE64(data);
}
/** A more secure, salted hash function.
* @note This hash is not stable between little and big endian.
*/
uint64_t GetHash(const uint256& salt) const;
};
/* uint256 from const char *.