/* * Utilities for working with hash values. * * Portions Copyright (c) 2017-2021, PostgreSQL Global Development Group */ #ifndef HASHFN_H #define HASHFN_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 uint32 hash_bytes(const unsigned char *k, int keylen); extern uint64 hash_bytes_extended(const unsigned char *k, int keylen, uint64 seed); extern uint32 hash_bytes_uint32(uint32 k); extern uint64 hash_bytes_uint32_extended(uint32 k, uint64 seed); #ifndef FRONTEND static inline Datum hash_any(const unsigned char *k, int keylen) { return UInt32GetDatum(hash_bytes(k, keylen)); } static inline Datum hash_any_extended(const unsigned char *k, int keylen, uint64 seed) { return UInt64GetDatum(hash_bytes_extended(k, keylen, seed)); } static inline Datum hash_uint32(uint32 k) { return UInt32GetDatum(hash_bytes_uint32(k)); } static inline Datum hash_uint32_extended(uint32 k, uint64 seed) { return UInt64GetDatum(hash_bytes_uint32_extended(k, seed)); } #endif extern uint32 string_hash(const void *key, Size keysize); extern uint32 tag_hash(const void *key, Size keysize); extern uint32 uint32_hash(const void *key, Size keysize); #define oid_hash uint32_hash /* Remove me eventually */ /* * 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 /* HASHFN_H */