/*------------------------------------------------------------------------- * * hashfn.c * Hash functions for use in dynahash.c hashtables * * * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/utils/hash/hashfn.c * * NOTES * It is expected that every bit of a hash function's 32-bit result is * as random as every other; failure to ensure this is likely to lead * to poor performance of hash tables. In most cases a hash * function should use hash_any() or its variant hash_uint32(). * *------------------------------------------------------------------------- */ #include "postgres.h" #include "access/hash.h" #include "utils/hsearch.h" /* * string_hash: hash function for keys that are NUL-terminated strings. * * NOTE: this is the default hash function if none is specified. */ uint32 string_hash(const void *key, Size keysize) { /* * If the string exceeds keysize-1 bytes, we want to hash only that many, * because when it is copied into the hash table it will be truncated at * that length. */ Size s_len = strlen((const char *) key); s_len = Min(s_len, keysize - 1); return DatumGetUInt32(hash_any((const unsigned char *) key, (int) s_len)); } /* * tag_hash: hash function for fixed-size tag values */ uint32 tag_hash(const void *key, Size keysize) { return DatumGetUInt32(hash_any((const unsigned char *) key, (int) keysize)); } /* * uint32_hash: hash function for keys that are uint32 or int32 * * (tag_hash works for this case too, but is slower) */ uint32 uint32_hash(const void *key, Size keysize) { Assert(keysize == sizeof(uint32)); return DatumGetUInt32(hash_uint32(*((const uint32 *) key))); } /* * bitmap_hash: hash function for keys that are (pointers to) Bitmapsets * * Note: don't forget to specify bitmap_match as the match function! */ uint32 bitmap_hash(const void *key, Size keysize) { Assert(keysize == sizeof(Bitmapset *)); return bms_hash_value(*((const Bitmapset *const *) key)); } /* * bitmap_match: match function to use with bitmap_hash */ int bitmap_match(const void *key1, const void *key2, Size keysize) { Assert(keysize == sizeof(Bitmapset *)); return !bms_equal(*((const Bitmapset *const *) key1), *((const Bitmapset *const *) key2)); }