[PATCH 02/17] bitops: Add generic parity calculation for u64

Kuan-Wei Chiu
2025-02-23T16:43:17Z

Several parts of the kernel open-code parity calculations using
different methods. Add a generic parity64() helper implemented with the
same efficient approach as parity8().

Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
include/linux/bitops.h | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index fb13dedad7aa..67677057f5e2 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -281,6 +281,28 @@ static inline int parity32(u32 val)
return (0x6996 >> (val & 0xf)) & 1;
}

+/**
+ * parity64 - get the parity of an u64 value
+ * @value: the value to be examined
+ *
+ * Determine the parity of the u64 argument.
+ *
+ * Returns:
+ * 0 for even parity, 1 for odd parity
+ */
+static inline int parity64(u64 val)
+{
+ /*
+ * One explanation of this algorithm:
+ * https://funloop.org/codex/problem/parity/README.html
+ */
+ val ^= val >> 32;
+ val ^= val >> 16;
+ val ^= val >> 8;
+ val ^= val >> 4;
+ return (0x6996 >> (val & 0xf)) & 1;
+}
+
/**
* __ffs64 - find first set bit in a 64 bit word
* @word: The 64 bit word
--
2.34.1