diff options
Diffstat (limited to 'src/backend/access/hash/hashfunc.c')
| -rw-r--r-- | src/backend/access/hash/hashfunc.c | 52 |
1 files changed, 42 insertions, 10 deletions
diff --git a/src/backend/access/hash/hashfunc.c b/src/backend/access/hash/hashfunc.c index d9b5524b0ab..39a58c0899a 100644 --- a/src/backend/access/hash/hashfunc.c +++ b/src/backend/access/hash/hashfunc.c @@ -1,19 +1,26 @@ /*------------------------------------------------------------------------- * * hashfunc.c - * Comparison functions for hash access method. + * Support functions for hash access method. * * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/access/hash/hashfunc.c,v 1.51 2007/04/02 03:49:37 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/access/hash/hashfunc.c,v 1.52 2007/06/01 15:33:18 tgl Exp $ * * NOTES * These functions are stored in pg_amproc. For each operator class - * defined on hash tables, they compute the hash value of the argument. + * defined for hash indexes, they compute the hash value of the argument. * + * Additional hash functions appear in /utils/adt/ files for various + * specialized datatypes. + * + * 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 joins, for example. In most cases a hash + * function should use hash_any() or its variant hash_uint32(). *------------------------------------------------------------------------- */ @@ -26,19 +33,19 @@ Datum hashchar(PG_FUNCTION_ARGS) { - PG_RETURN_UINT32(~((uint32) PG_GETARG_CHAR(0))); + return hash_uint32((int32) PG_GETARG_CHAR(0)); } Datum hashint2(PG_FUNCTION_ARGS) { - PG_RETURN_UINT32(~((uint32) PG_GETARG_INT16(0))); + return hash_uint32((int32) PG_GETARG_INT16(0)); } Datum hashint4(PG_FUNCTION_ARGS) { - PG_RETURN_UINT32(~PG_GETARG_UINT32(0)); + return hash_uint32(PG_GETARG_INT32(0)); } Datum @@ -59,23 +66,23 @@ hashint8(PG_FUNCTION_ARGS) lohalf ^= (val >= 0) ? hihalf : ~hihalf; - PG_RETURN_UINT32(~lohalf); + return hash_uint32(lohalf); #else /* here if we can't count on "x >> 32" to work sanely */ - PG_RETURN_UINT32(~((uint32) PG_GETARG_INT64(0))); + return hash_uint32((int32) PG_GETARG_INT64(0)); #endif } Datum hashoid(PG_FUNCTION_ARGS) { - PG_RETURN_UINT32(~((uint32) PG_GETARG_OID(0))); + return hash_uint32((uint32) PG_GETARG_OID(0)); } Datum hashenum(PG_FUNCTION_ARGS) { - PG_RETURN_UINT32(~((uint32) PG_GETARG_OID(0))); + return hash_uint32((uint32) PG_GETARG_OID(0)); } Datum @@ -283,6 +290,31 @@ hash_any(register const unsigned char *k, register int keylen) /* case 0: nothing left to add */ } mix(a, b, c); + + /* report the result */ + return UInt32GetDatum(c); +} + +/* + * hash_uint32() -- hash a 32-bit value + * + * This has the same result (at least on little-endian machines) as + * hash_any(&k, sizeof(uint32)) + * but is faster and doesn't force the caller to store k into memory. + */ +Datum +hash_uint32(uint32 k) +{ + register uint32 a, + b, + c; + + a = 0x9e3779b9 + k; + b = 0x9e3779b9; + c = 3923095 + (uint32) sizeof(uint32); + + mix(a, b, c); + /* report the result */ return UInt32GetDatum(c); } |