lib/find: introduce find_nth_and_andnot_bit

In the following patches the function is used to implement in-place bitmaps
traversing without storing intermediate result in temporary bitmaps.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Peter Lafreniere <peter@n8pjl.ca>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/find.h

@@ -22,6 +22,9 @@ unsigned long __find_nth_and_bit(const unsigned long *addr1, const unsigned long
 				unsigned long size, unsigned long n);
 unsigned long __find_nth_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
 					unsigned long size, unsigned long n);
+unsigned long __find_nth_and_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
+					const unsigned long *addr3, unsigned long size,
+					unsigned long n);
 extern unsigned long _find_first_and_bit(const unsigned long *addr1,
 					 const unsigned long *addr2, unsigned long size);
 extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size);
@@ -255,6 +258,36 @@ unsigned long find_nth_andnot_bit(const unsigned long *addr1, const unsigned lon
 	return __find_nth_andnot_bit(addr1, addr2, size, n);
 }
 
+/**
+ * find_nth_and_andnot_bit - find N'th set bit in 2 memory regions,
+ *			     excluding those set in 3rd region
+ * @addr1: The 1st address to start the search at
+ * @addr2: The 2nd address to start the search at
+ * @addr3: The 3rd address to start the search at
+ * @size: The maximum number of bits to search
+ * @n: The number of set bit, which position is needed, counting from 0
+ *
+ * Returns the bit number of the N'th set bit.
+ * If no such, returns @size.
+ */
+static __always_inline
+unsigned long find_nth_and_andnot_bit(const unsigned long *addr1,
+					const unsigned long *addr2,
+					const unsigned long *addr3,
+					unsigned long size, unsigned long n)
+{
+	if (n >= size)
+		return size;
+
+	if (small_const_nbits(size)) {
+		unsigned long val =  *addr1 & *addr2 & (~*addr3) & GENMASK(size - 1, 0);
+
+		return val ? fns(val, n) : size;
+	}
+
+	return __find_nth_and_andnot_bit(addr1, addr2, addr3, size, n);
+}
+
 #ifndef find_first_and_bit
 /**
  * find_first_and_bit - find the first set bit in both memory regions

lib/find_bit.c

@@ -155,6 +155,15 @@ unsigned long __find_nth_andnot_bit(const unsigned long *addr1, const unsigned l
 }
 EXPORT_SYMBOL(__find_nth_andnot_bit);
 
+unsigned long __find_nth_and_andnot_bit(const unsigned long *addr1,
+					const unsigned long *addr2,
+					const unsigned long *addr3,
+					unsigned long size, unsigned long n)
+{
+	return FIND_NTH_BIT(addr1[idx] & addr2[idx] & ~addr3[idx], size, n);
+}
+EXPORT_SYMBOL(__find_nth_and_andnot_bit);
+
 #ifndef find_next_and_bit
 unsigned long _find_next_and_bit(const unsigned long *addr1, const unsigned long *addr2,
 					unsigned long nbits, unsigned long start)