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//-----------------------------------------------------------------------------
// MurmurHash2 was written by Austin Appleby, and is placed in the public
// domain. The author hereby disclaims copyright to this source code.
// Note - This code makes a few assumptions about how your machine behaves -
// 1. We can read a 4-byte value from any address without crashing
// 2. sizeof(int) == 4
// And it has a few limitations -
// 1. It will not work incrementally.
// 2. It will not produce the same results on little-endian and big-endian
// machines.
#include "MurmurHash2.h"
//-----------------------------------------------------------------------------
// Platform-specific functions and macros
// Microsoft Visual Studio
#if defined(_MSC_VER)
#define BIG_CONSTANT(x) (x)
// Other compilers
#else // defined(_MSC_VER)
#define BIG_CONSTANT(x) (x##LLU)
#endif // !defined(_MSC_VER)
//-----------------------------------------------------------------------------
uint32_t MurmurHash2 ( const void * key, int len, uint32_t seed )
{
// 'm' and 'r' are mixing constants generated offline.
// They're not really 'magic', they just happen to work well.
const uint32_t m = 0x5bd1e995;
const int r = 24;
// Initialize the hash to a 'random' value
uint32_t h = seed ^ len;
// Mix 4 bytes at a time into the hash
const unsigned char * data = (const unsigned char *)key;
while(len >= 4)
{
uint32_t k = *(uint32_t*)data;
k *= m;
k ^= k >> r;
k *= m;
h *= m;
h ^= k;
data += 4;
len -= 4;
}
// Handle the last few bytes of the input array
switch(len)
{
case 3: h ^= data[2] << 16;
case 2: h ^= data[1] << 8;
case 1: h ^= data[0];
h *= m;
};
// Do a few final mixes of the hash to ensure the last few
// bytes are well-incorporated.
h ^= h >> 13;
h *= m;
h ^= h >> 15;
return h;
}
//-----------------------------------------------------------------------------
// MurmurHash2, 64-bit versions, by Austin Appleby
// The same caveats as 32-bit MurmurHash2 apply here - beware of alignment
// and endian-ness issues if used across multiple platforms.
// 64-bit hash for 64-bit platforms
uint64_t MurmurHash64A ( const void * key, int len, uint64_t seed )
{
const uint64_t m = BIG_CONSTANT(0xc6a4a7935bd1e995);
const int r = 47;
uint64_t h = seed ^ (len * m);
const uint64_t * data = (const uint64_t *)key;
const uint64_t * end = data + (len/8);
while(data != end)
{
uint64_t k = *data++;
k *= m;
k ^= k >> r;
k *= m;
h ^= k;
h *= m;
}
const unsigned char * data2 = (const unsigned char*)data;
switch(len & 7)
{
case 7: h ^= uint64_t(data2[6]) << 48;
case 6: h ^= uint64_t(data2[5]) << 40;
case 5: h ^= uint64_t(data2[4]) << 32;
case 4: h ^= uint64_t(data2[3]) << 24;
case 3: h ^= uint64_t(data2[2]) << 16;
case 2: h ^= uint64_t(data2[1]) << 8;
case 1: h ^= uint64_t(data2[0]);
h *= m;
};
h ^= h >> r;
h *= m;
h ^= h >> r;
return h;
}
// 64-bit hash for 32-bit platforms
uint64_t MurmurHash64B ( const void * key, int len, uint64_t seed )
{
const uint32_t m = 0x5bd1e995;
const int r = 24;
uint32_t h1 = uint32_t(seed) ^ len;
uint32_t h2 = uint32_t(seed >> 32);
const uint32_t * data = (const uint32_t *)key;
while(len >= 8)
{
uint32_t k1 = *data++;
k1 *= m; k1 ^= k1 >> r; k1 *= m;
h1 *= m; h1 ^= k1;
len -= 4;
uint32_t k2 = *data++;
k2 *= m; k2 ^= k2 >> r; k2 *= m;
h2 *= m; h2 ^= k2;
len -= 4;
}
if(len >= 4)
{
uint32_t k1 = *data++;
k1 *= m; k1 ^= k1 >> r; k1 *= m;
h1 *= m; h1 ^= k1;
len -= 4;
}
switch(len)
{
case 3: h2 ^= ((unsigned char*)data)[2] << 16;
case 2: h2 ^= ((unsigned char*)data)[1] << 8;
case 1: h2 ^= ((unsigned char*)data)[0];
h2 *= m;
};
h1 ^= h2 >> 18; h1 *= m;
h2 ^= h1 >> 22; h2 *= m;
h1 ^= h2 >> 17; h1 *= m;
h2 ^= h1 >> 19; h2 *= m;
uint64_t h = h1;
h = (h << 32) | h2;
return h;
}
//-----------------------------------------------------------------------------
// MurmurHash2A, by Austin Appleby
// This is a variant of MurmurHash2 modified to use the Merkle-Damgard
// construction. Bulk speed should be identical to Murmur2, small-key speed
// will be 10%-20% slower due to the added overhead at the end of the hash.
// This variant fixes a minor issue where null keys were more likely to
// collide with each other than expected, and also makes the function
// more amenable to incremental implementations.
#define mmix(h,k) { k *= m; k ^= k >> r; k *= m; h *= m; h ^= k; }
uint32_t MurmurHash2A ( const void * key, int len, uint32_t seed )
{
const uint32_t m = 0x5bd1e995;
const int r = 24;
uint32_t l = len;
const unsigned char * data = (const unsigned char *)key;
uint32_t h = seed;
while(len >= 4)
{
uint32_t k = *(uint32_t*)data;
mmix(h,k);
data += 4;
len -= 4;
}
uint32_t t = 0;
switch(len)
{
case 3: t ^= data[2] << 16;
case 2: t ^= data[1] << 8;
case 1: t ^= data[0];
};
mmix(h,t);
mmix(h,l);
h ^= h >> 13;
h *= m;
h ^= h >> 15;
return h;
}
//-----------------------------------------------------------------------------
// CMurmurHash2A, by Austin Appleby
// This is a sample implementation of MurmurHash2A designed to work
// incrementally.
// Usage -
// CMurmurHash2A hasher
// hasher.Begin(seed);
// hasher.Add(data1,size1);
// hasher.Add(data2,size2);
// ...
// hasher.Add(dataN,sizeN);
// uint32_t hash = hasher.End()
class CMurmurHash2A
{
public:
void Begin ( uint32_t seed = 0 )
{
m_hash = seed;
m_tail = 0;
m_count = 0;
m_size = 0;
}
void Add ( const unsigned char * data, int len )
{
m_size += len;
MixTail(data,len);
while(len >= 4)
{
uint32_t k = *(uint32_t*)data;
mmix(m_hash,k);
data += 4;
len -= 4;
}
MixTail(data,len);
}
uint32_t End ( void )
{
mmix(m_hash,m_tail);
mmix(m_hash,m_size);
m_hash ^= m_hash >> 13;
m_hash *= m;
m_hash ^= m_hash >> 15;
return m_hash;
}
private:
static const uint32_t m = 0x5bd1e995;
static const int r = 24;
void MixTail ( const unsigned char * & data, int & len )
{
while( len && ((len<4) || m_count) )
{
m_tail |= (*data++) << (m_count * 8);
m_count++;
len--;
if(m_count == 4)
{
mmix(m_hash,m_tail);
m_tail = 0;
m_count = 0;
}
}
}
uint32_t m_hash;
uint32_t m_tail;
uint32_t m_count;
uint32_t m_size;
};
//-----------------------------------------------------------------------------
// MurmurHashNeutral2, by Austin Appleby
// Same as MurmurHash2, but endian- and alignment-neutral.
// Half the speed though, alas.
uint32_t MurmurHashNeutral2 ( const void * key, int len, uint32_t seed )
{
const uint32_t m = 0x5bd1e995;
const int r = 24;
uint32_t h = seed ^ len;
const unsigned char * data = (const unsigned char *)key;
while(len >= 4)
{
uint32_t k;
k = data[0];
k |= data[1] << 8;
k |= data[2] << 16;
k |= data[3] << 24;
k *= m;
k ^= k >> r;
k *= m;
h *= m;
h ^= k;
data += 4;
len -= 4;
}
switch(len)
{
case 3: h ^= data[2] << 16;
case 2: h ^= data[1] << 8;
case 1: h ^= data[0];
h *= m;
};
h ^= h >> 13;
h *= m;
h ^= h >> 15;
return h;
}
//-----------------------------------------------------------------------------
// MurmurHashAligned2, by Austin Appleby
// Same algorithm as MurmurHash2, but only does aligned reads - should be safer
// on certain platforms.
// Performance will be lower than MurmurHash2
#define MIX(h,k,m) { k *= m; k ^= k >> r; k *= m; h *= m; h ^= k; }
uint32_t MurmurHashAligned2 ( const void * key, int len, uint32_t seed )
{
const uint32_t m = 0x5bd1e995;
const int r = 24;
const unsigned char * data = (const unsigned char *)key;
uint32_t h = seed ^ len;
int align = (uint64_t)data & 3;
if(align && (len >= 4))
{
// Pre-load the temp registers
uint32_t t = 0, d = 0;
switch(align)
{
case 1: t |= data[2] << 16;
case 2: t |= data[1] << 8;
case 3: t |= data[0];
}
t <<= (8 * align);
data += 4-align;
len -= 4-align;
int sl = 8 * (4-align);
int sr = 8 * align;
// Mix
while(len >= 4)
{
d = *(uint32_t *)data;
t = (t >> sr) | (d << sl);
uint32_t k = t;
MIX(h,k,m);
t = d;
data += 4;
len -= 4;
}
// Handle leftover data in temp registers
d = 0;
if(len >= align)
{
switch(align)
{
case 3: d |= data[2] << 16;
case 2: d |= data[1] << 8;
case 1: d |= data[0];
}
uint32_t k = (t >> sr) | (d << sl);
MIX(h,k,m);
data += align;
len -= align;
//----------
// Handle tail bytes
switch(len)
{
case 3: h ^= data[2] << 16;
case 2: h ^= data[1] << 8;
case 1: h ^= data[0];
h *= m;
};
}
else
{
switch(len)
{
case 3: d |= data[2] << 16;
case 2: d |= data[1] << 8;
case 1: d |= data[0];
case 0: h ^= (t >> sr) | (d << sl);
h *= m;
}
}
h ^= h >> 13;
h *= m;
h ^= h >> 15;
return h;
}
else
{
while(len >= 4)
{
uint32_t k = *(uint32_t *)data;
MIX(h,k,m);
data += 4;
len -= 4;
}
//----------
// Handle tail bytes
switch(len)
{
case 3: h ^= data[2] << 16;
case 2: h ^= data[1] << 8;
case 1: h ^= data[0];
h *= m;
};
h ^= h >> 13;
h *= m;
h ^= h >> 15;
return h;
}
}
//-----------------------------------------------------------------------------
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