linux-kernel - [PATCH 2/4] find: add find_first_andnot

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Message-ID: <20250407153856.133093-3-yury.norov@gmail.com>
Date: Mon,  7 Apr 2025 11:38:53 -0400
From: Yury Norov <yury.norov@...il.com>
To: Tony Luck <tony.luck@...el.com>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Yury Norov [NVIDIA]" <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/4] find: add find_first_andnot_bit()

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

The function helps to implement cpumask_andnot() APIs.

Signed-off-by: Yury Norov [NVIDIA] <yury.norov@...il.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