From 81c5e46c490e2426db243eada186995da5bb0ba7 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Thu, 31 Aug 2017 22:21:21 -0400
Subject: Introduce 64-bit hash functions with a 64-bit seed.

This will be useful for hash partitioning, which needs a way to seed
the hash functions to avoid problems such as a hash index on a hash
partitioned table clumping all values into a small portion of the
bucket space; it's also useful for anything that wants a 64-bit hash
value rather than a 32-bit hash value.

Just in case somebody wants a 64-bit hash value that is compatible
with the existing 32-bit hash values, make the low 32-bits of the
64-bit hash value match the 32-bit hash value when the seed is 0.

Robert Haas and Amul Sul

Discussion: http://postgr.es/m/CA+Tgmoafx2yoJuhCQQOL5CocEi-w_uG4S2xT0EtgiJnPGcHW3g@mail.gmail.com
---
 src/backend/utils/adt/jsonb_util.c | 43 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

(limited to 'src/backend/utils/adt/jsonb_util.c')

diff --git a/src/backend/utils/adt/jsonb_util.c b/src/backend/utils/adt/jsonb_util.c
index 4850569bb5e..d425f324038 100644
--- a/src/backend/utils/adt/jsonb_util.c
+++ b/src/backend/utils/adt/jsonb_util.c
@@ -1249,6 +1249,49 @@ JsonbHashScalarValue(const JsonbValue *scalarVal, uint32 *hash)
 	*hash ^= tmp;
 }
 
+/*
+ * Hash a value to a 64-bit value, with a seed. Otherwise, similar to
+ * JsonbHashScalarValue.
+ */
+void
+JsonbHashScalarValueExtended(const JsonbValue *scalarVal, uint64 *hash,
+							 uint64 seed)
+{
+	uint64		tmp;
+
+	switch (scalarVal->type)
+	{
+		case jbvNull:
+			tmp = seed + 0x01;
+			break;
+		case jbvString:
+			tmp = DatumGetUInt64(hash_any_extended((const unsigned char *) scalarVal->val.string.val,
+												   scalarVal->val.string.len,
+												   seed));
+			break;
+		case jbvNumeric:
+			tmp = DatumGetUInt64(DirectFunctionCall2(hash_numeric_extended,
+													 NumericGetDatum(scalarVal->val.numeric),
+													 UInt64GetDatum(seed)));
+			break;
+		case jbvBool:
+			if (seed)
+				tmp = DatumGetUInt64(DirectFunctionCall2(hashcharextended,
+														 BoolGetDatum(scalarVal->val.boolean),
+														 UInt64GetDatum(seed)));
+			else
+				tmp = scalarVal->val.boolean ? 0x02 : 0x04;
+
+			break;
+		default:
+			elog(ERROR, "invalid jsonb scalar type");
+			break;
+	}
+
+	*hash = ROTATE_HIGH_AND_LOW_32BITS(*hash);
+	*hash ^= tmp;
+}
+
 /*
  * Are two scalar JsonbValues of the same type a and b equal?
  */
-- 
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