[PATCH 2/4] find: add find_first_andnot_bit()

Yury Norov
2025-04-07T15:39:02Z

From: Yury Norov [NVIDIA] <yury.norov@gmail.com>

The function helps to implement cpumask_andnot() APIs.

Signed-off-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
---
include/linux/find.h | 25 +++++++++++++++++++++++++
lib/find_bit.c | 11 +++++++++++
2 files changed, 36 insertions(+)

diff --git a/include/linux/find.h b/include/linux/find.h
index 68685714bc18..d1578cfb667c 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -29,6 +29,8 @@ unsigned long __find_nth_and_andnot_bit(const unsigned long *addr1, const unsign
unsigned long n);
extern unsigned long _find_first_and_bit(const unsigned long *addr1,
const unsigned long *addr2, unsigned long size);
+unsigned long _find_first_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
+ unsigned long size);
unsigned long _find_first_and_and_bit(const unsigned long *addr1, const unsigned long *addr2,
const unsigned long *addr3, unsigned long size);
extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size);
@@ -347,6 +349,29 @@ unsigned long find_first_and_bit(const unsigned long *addr1,
}
#endif

+/**
+ * find_first_andnot_bit - find the first bit set in 1st memory region and unset in 2nd
+ * @addr1: The first address to base the search on
+ * @addr2: The second address to base the search on
+ * @size: The bitmap size in bits
+ *
+ * Returns the bit number for the matched bit
+ * If no bits are set, returns >= @size.
+ */
+static __always_inline
+unsigned long find_first_andnot_bit(const unsigned long *addr1,
+ const unsigned long *addr2,
+ unsigned long size)
+{
+ if (small_const_nbits(size)) {
+ unsigned long val = *addr1 & (~*addr2) & GENMASK(size - 1, 0);
+
+ return val ? __ffs(val) : size;
+ }
+
+ return _find_first_andnot_bit(addr1, addr2, size);
+}
+
/**
* find_first_and_and_bit - find the first set bit in 3 memory regions
* @addr1: The first address to base the search on
diff --git a/lib/find_bit.c b/lib/find_bit.c
index 0836bb3d76c5..06b6342aa3ae 100644
--- a/lib/find_bit.c
+++ b/lib/find_bit.c
@@ -116,6 +116,17 @@ unsigned long _find_first_and_bit(const unsigned long *addr1,
EXPORT_SYMBOL(_find_first_and_bit);
#endif

+/*
+ * Find the first bit set in 1st memory region and unset in 2nd.
+ */
+unsigned long _find_first_andnot_bit(const unsigned long *addr1,
+ const unsigned long *addr2,
+ unsigned long size)
+{
+ return FIND_FIRST_BIT(addr1[idx] & ~addr2[idx], /* nop */, size);
+}
+EXPORT_SYMBOL(_find_first_andnot_bit);
+
/*
* Find the first set bit in three memory regions.
*/
--
2.43.0