diff options
Diffstat (limited to 'src/backend/nodes/bitmapset.c')
| -rw-r--r-- | src/backend/nodes/bitmapset.c | 27 |
1 files changed, 26 insertions, 1 deletions
diff --git a/src/backend/nodes/bitmapset.c b/src/backend/nodes/bitmapset.c index 699f0439ffc..5f4ca9a779b 100644 --- a/src/backend/nodes/bitmapset.c +++ b/src/backend/nodes/bitmapset.c @@ -14,7 +14,7 @@ * Copyright (c) 2003-2005, PostgreSQL Global Development Group * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/nodes/bitmapset.c,v 1.7 2005/01/01 20:44:15 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/nodes/bitmapset.c,v 1.8 2005/06/08 23:02:04 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -763,3 +763,28 @@ bms_first_member(Bitmapset *a) } return -1; } + +/* + * bms_hash_value - compute a hash key for a Bitmapset + * + * Note: we must ensure that any two bitmapsets that are bms_equal() will + * hash to the same value; in practice this means that trailing all-zero + * words cannot affect the result. Longitudinal XOR provides a reasonable + * hash value that has this property. + */ +uint32 +bms_hash_value(const Bitmapset *a) +{ + bitmapword result = 0; + int nwords; + int wordnum; + + if (a == NULL) + return 0; /* All empty sets hash to 0 */ + nwords = a->nwords; + for (wordnum = 0; wordnum < nwords; wordnum++) + { + result ^= a->words[wordnum]; + } + return (uint32) result; +} |