builtinconstants: define constants for unique int bit segments

This patch defines constants for the sizes and bitmasks for each
bit segment in a unique int generated for row IDs.

Release note: None

pkg/sql/row/row_converter.go

@@ -489,7 +489,7 @@ func NewDatumRowConverter(
 	return c, nil
 }
 
-const rowIDBits = 64 - builtinconstants.NodeIDBits
+const rowIDBits = 64 - builtinconstants.UniqueIntNodeIDBits
 
 // Row inserts kv operations into the current kv batch, and triggers a SendBatch
 // if necessary.

pkg/sql/sem/builtins/builtinconstants/constants.go

@@ -76,6 +76,28 @@ const (
 	CreateSchemaTelemetryJobBuiltinName = "crdb_internal.create_sql_schema_telemetry_job"
 )
 
-// NodeIDBits is the number of bits stored in the lower portion of
-// GenerateUniqueInt.
-const NodeIDBits = 15
+// A unique int generated by GenerateUniqueInt is a 64-bit integer with
+// the following format:
+//
+//	[1 leading zero bit][48 bits for timestamp][15 bits for nodeID]
+const (
+	// UniqueIntLeadingZeroBits is the number of leading zero bits in a unique
+	// int generated by GenerateUniqueInt.
+	UniqueIntLeadingZeroBits = 1
+
+	// UniqueIntTimestampBits is the number of bits in the timestamp segment
+	// in a unique int generated by GenerateUniqueInt.
+	UniqueIntTimestampBits = 48
+
+	// UniqueIntNodeIDBits is the number of bits in the node ID segment
+	// in a unique int generated by GenerateUniqueInt.
+	UniqueIntNodeIDBits = 15
+
+	// UniqueIntNodeIDMask is a bitmask for the node ID in a unique int
+	// generated by GenerateUniqueInt.
+	UniqueIntNodeIDMask = 1<<UniqueIntNodeIDBits - 1
+
+	// UniqueIntTimestampMask is a bitmask for the timestamp in a unique int
+	// generated by GenerateUniqueInt.
+	UniqueIntTimestampMask = (1<<UniqueIntTimestampBits - 1) << UniqueIntNodeIDBits
+)

pkg/sql/sem/builtins/builtins.go

@@ -9859,7 +9859,7 @@ func GenerateUniqueInt(instanceID ProcessUniqueID) tree.DInt {
 func GenerateUniqueID(instanceID int32, timestamp uint64) tree.DInt {
 	// We xor in the instanceID so that instanceIDs larger than 32K will flip bits
 	// in the timestamp portion of the final value instead of always setting them.
-	id := (timestamp << builtinconstants.NodeIDBits) ^ uint64(instanceID)
+	id := (timestamp << builtinconstants.UniqueIntNodeIDBits) ^ uint64(instanceID)
 	return tree.DInt(id)
 }