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/*
* Utilities for working with hash values.
*
* Portions Copyright (c) 2017-2019, PostgreSQL Global Development Group
*/
#ifndef HASHUTILS_H
#define HASHUTILS_H
/*
* Rotate the high 32 bits and the low 32 bits separately. The standard
* hash function sometimes rotates the low 32 bits by one bit when
* combining elements. We want extended hash functions to be compatible with
* that algorithm when the seed is 0, so we can't just do a normal rotation.
* This works, though.
*/
#define ROTATE_HIGH_AND_LOW_32BITS(v) \
((((v) << 1) & UINT64CONST(0xfffffffefffffffe)) | \
(((v) >> 31) & UINT64CONST(0x100000001)))
extern Datum hash_any(register const unsigned char *k, register int keylen);
extern Datum hash_any_extended(register const unsigned char *k,
register int keylen, uint64 seed);
extern Datum hash_uint32(uint32 k);
extern Datum hash_uint32_extended(uint32 k, uint64 seed);
/*
* Combine two 32-bit hash values, resulting in another hash value, with
* decent bit mixing.
*
* Similar to boost's hash_combine().
*/
static inline uint32
hash_combine(uint32 a, uint32 b)
{
a ^= b + 0x9e3779b9 + (a << 6) + (a >> 2);
return a;
}
/*
* Combine two 64-bit hash values, resulting in another hash value, using the
* same kind of technique as hash_combine(). Testing shows that this also
* produces good bit mixing.
*/
static inline uint64
hash_combine64(uint64 a, uint64 b)
{
/* 0x49a0f4dd15e5a8e3 is 64bit random data */
a ^= b + UINT64CONST(0x49a0f4dd15e5a8e3) + (a << 54) + (a >> 7);
return a;
}
/*
* Simple inline murmur hash implementation hashing a 32 bit integer, for
* performance.
*/
static inline uint32
murmurhash32(uint32 data)
{
uint32 h = data;
h ^= h >> 16;
h *= 0x85ebca6b;
h ^= h >> 13;
h *= 0xc2b2ae35;
h ^= h >> 16;
return h;
}
#endif /* HASHUTILS_H */
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