net: add rps_tag_ptr type and helpers

Add a new rps_tag_ptr type to encode a pointer and a size
to a power-of-two table.

Three helpers are added converting an rps_tag_ptr to:

1) A log of the size.

2) A mask : (size - 1).

3) A pointer to the array.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260302181432.1836150-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/rps-types.h

@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _NET_RPS_TYPES_H
+#define _NET_RPS_TYPES_H
+
+/* Define a rps_tag_ptr:
+ * Low order 5 bits are used to store the ilog2(size) of an RPS table.
+ */
+typedef unsigned long rps_tag_ptr;
+
+static inline u8 rps_tag_to_log(rps_tag_ptr tag_ptr)
+{
+	return tag_ptr & 31U;
+}
+
+static inline u32 rps_tag_to_mask(rps_tag_ptr tag_ptr)
+{
+	return (1U << rps_tag_to_log(tag_ptr)) - 1;
+}
+
+static inline void *rps_tag_to_table(rps_tag_ptr tag_ptr)
+{
+	return (void *)(tag_ptr & ~31UL);
+}
+#endif /* _NET_RPS_TYPES_H */