Add Wang hash functions

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kaetemi 2015-03-29 03:14:06 +02:00
parent 10aded4c42
commit 71cc7c3197

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// Public domain hash functions
#ifndef NLMISC_WANG_HASH_H
#define NLMISC_WANG_HASH_H
#include "types_nl.h"
namespace NLMISC {
// http://burtleburtle.net/bob/hash/integer.html
inline uint32 wangHash(uint32 a)
{
a = (a ^ 61) ^ (a >> 16);
a = a + (a << 3);
a = a ^ (a >> 4);
a = a * 0x27d4eb2d;
a = a ^ (a >> 15);
return a;
}
// http://naml.us/blog/2012/03
inline uint64 wangHash64(uint64 key)
{
key = (~key) + (key << 21); // key = (key << 21) - key - 1;
key = key ^ (key >> 24);
key = (key + (key << 3)) + (key << 8); // key * 265
key = key ^ (key >> 14);
key = (key + (key << 2)) + (key << 4); // key * 21
key = key ^ (key >> 28);
key = key + (key << 31);
return key;
}
// http://naml.us/blog/2012/03 Inverse 64-bit wang hash
inline uint64 wangHash64Inv(uint64 key)
{
uint64 tmp;
// Invert key = key + (key << 31)
tmp = key - (key << 31);
key = key - (tmp << 31);
// Invert key = key ^ (key >> 28)
tmp = key^key >> 28;
key = key^tmp >> 28;
// Invert key *= 21
key *= 14933078535860113213u;
// Invert key = key ^ (key >> 14)
tmp = key^key >> 14;
tmp = key^tmp >> 14;
tmp = key^tmp >> 14;
key = key^tmp >> 14;
// Invert key *= 265
key *= 15244667743933553977u;
// Invert key = key ^ (key >> 24)
tmp = key^key >> 24;
key = key^tmp >> 24;
// Invert key = (~key) + (key << 21)
tmp = ~key;
tmp = ~(key - (tmp << 21));
tmp = ~(key - (tmp << 21));
key = ~(key - (tmp << 21));
return key;
}
} /* namespace NLMISC */
#endif // NLMISC_WANG_HASH_H