t8-mod/deps/xxhash/xxhash64.h
2024-02-15 15:46:47 -05:00

203 lines
6.2 KiB
C++

// //////////////////////////////////////////////////////////
// xxhash64.h
// Copyright (c) 2016 Stephan Brumme. All rights reserved.
// see http://create.stephan-brumme.com/disclaimer.html
//
#pragma once
#include <stdint.h> // for uint32_t and uint64_t
/// XXHash (64 bit), based on Yann Collet's descriptions, see http://cyan4973.github.io/xxHash/
/** How to use:
uint64_t myseed = 0;
XXHash64 myhash(myseed);
myhash.add(pointerToSomeBytes, numberOfBytes);
myhash.add(pointerToSomeMoreBytes, numberOfMoreBytes); // call add() as often as you like to ...
// and compute hash:
uint64_t result = myhash.hash();
// or all of the above in one single line:
uint64_t result2 = XXHash64::hash(mypointer, numBytes, myseed);
Note: my code is NOT endian-aware !
**/
class XXHash64
{
public:
/// create new XXHash (64 bit)
/** @param seed your seed value, even zero is a valid seed **/
explicit XXHash64(uint64_t seed)
{
state[0] = seed + Prime1 + Prime2;
state[1] = seed + Prime2;
state[2] = seed;
state[3] = seed - Prime1;
bufferSize = 0;
totalLength = 0;
}
/// add a chunk of bytes
/** @param input pointer to a continuous block of data
@param length number of bytes
@return false if parameters are invalid / zero **/
bool add(const void* input, uint64_t length)
{
// no data ?
if (!input || length == 0)
return false;
totalLength += length;
// byte-wise access
const unsigned char* data = (const unsigned char*)input;
// unprocessed old data plus new data still fit in temporary buffer ?
if (bufferSize + length < MaxBufferSize)
{
// just add new data
while (length-- > 0)
buffer[bufferSize++] = *data++;
return true;
}
// point beyond last byte
const unsigned char* stop = data + length;
const unsigned char* stopBlock = stop - MaxBufferSize;
// some data left from previous update ?
if (bufferSize > 0)
{
// make sure temporary buffer is full (16 bytes)
while (bufferSize < MaxBufferSize)
buffer[bufferSize++] = *data++;
// process these 32 bytes (4x8)
process(buffer, state[0], state[1], state[2], state[3]);
}
// copying state to local variables helps optimizer A LOT
uint64_t s0 = state[0], s1 = state[1], s2 = state[2], s3 = state[3];
// 32 bytes at once
while (data <= stopBlock)
{
// local variables s0..s3 instead of state[0]..state[3] are much faster
process(data, s0, s1, s2, s3);
data += 32;
}
// copy back
state[0] = s0; state[1] = s1; state[2] = s2; state[3] = s3;
// copy remainder to temporary buffer
bufferSize = stop - data;
for (uint64_t i = 0; i < bufferSize; i++)
buffer[i] = data[i];
// done
return true;
}
/// get current hash
/** @return 64 bit XXHash **/
uint64_t hash() const
{
// fold 256 bit state into one single 64 bit value
uint64_t result;
if (totalLength >= MaxBufferSize)
{
result = rotateLeft(state[0], 1) +
rotateLeft(state[1], 7) +
rotateLeft(state[2], 12) +
rotateLeft(state[3], 18);
result = (result ^ processSingle(0, state[0])) * Prime1 + Prime4;
result = (result ^ processSingle(0, state[1])) * Prime1 + Prime4;
result = (result ^ processSingle(0, state[2])) * Prime1 + Prime4;
result = (result ^ processSingle(0, state[3])) * Prime1 + Prime4;
}
else
{
// internal state wasn't set in add(), therefore original seed is still stored in state2
result = state[2] + Prime5;
}
result += totalLength;
// process remaining bytes in temporary buffer
const unsigned char* data = buffer;
// point beyond last byte
const unsigned char* stop = data + bufferSize;
// at least 8 bytes left ? => eat 8 bytes per step
for (; data + 8 <= stop; data += 8)
result = rotateLeft(result ^ processSingle(0, *(uint64_t*)data), 27) * Prime1 + Prime4;
// 4 bytes left ? => eat those
if (data + 4 <= stop)
{
result = rotateLeft(result ^ (*(uint32_t*)data) * Prime1, 23) * Prime2 + Prime3;
data += 4;
}
// take care of remaining 0..3 bytes, eat 1 byte per step
while (data != stop)
result = rotateLeft(result ^ (*data++) * Prime5, 11) * Prime1;
// mix bits
result ^= result >> 33;
result *= Prime2;
result ^= result >> 29;
result *= Prime3;
result ^= result >> 32;
return result;
}
/// combine constructor, add() and hash() in one static function (C style)
/** @param input pointer to a continuous block of data
@param length number of bytes
@param seed your seed value, e.g. zero is a valid seed
@return 64 bit XXHash **/
static uint64_t hash(const void* input, uint64_t length, uint64_t seed)
{
XXHash64 hasher(seed);
hasher.add(input, length);
return hasher.hash();
}
private:
/// magic constants :-)
static const uint64_t Prime1 = 11400714785074694791ULL;
static const uint64_t Prime2 = 14029467366897019727ULL;
static const uint64_t Prime3 = 1609587929392839161ULL;
static const uint64_t Prime4 = 9650029242287828579ULL;
static const uint64_t Prime5 = 2870177450012600261ULL;
/// temporarily store up to 31 bytes between multiple add() calls
static const uint64_t MaxBufferSize = 31+1;
uint64_t state[4];
unsigned char buffer[MaxBufferSize];
uint64_t bufferSize;
uint64_t totalLength;
/// rotate bits, should compile to a single CPU instruction (ROL)
static inline uint64_t rotateLeft(uint64_t x, unsigned char bits)
{
return (x << bits) | (x >> (64 - bits));
}
/// process a single 64 bit value
static inline uint64_t processSingle(uint64_t previous, uint64_t input)
{
return rotateLeft(previous + input * Prime2, 31) * Prime1;
}
/// process a block of 4x4 bytes, this is the main part of the XXHash32 algorithm
static inline void process(const void* data, uint64_t& state0, uint64_t& state1, uint64_t& state2, uint64_t& state3)
{
const uint64_t* block = (const uint64_t*) data;
state0 = processSingle(state0, block[0]);
state1 = processSingle(state1, block[1]);
state2 = processSingle(state2, block[2]);
state3 = processSingle(state3, block[3]);
}
};