[PATCH v2 1/5] bitops: Introduce find_next_andnot_bit()

[Valentin Schneider]

In preparation of introducing for_each_cpu_andnot(), add a variant of
find_next_bit() that negate the bits in @addr2 when ANDing them with the
bits in @addr1.

Note that the _find_next_bit() @invert argument now gets split into two:
@invert1 for words in @addr1, @invert2 for words in @addr2. The only
current users of _find_next_bit() with @invert set are:
  o find_next_zero_bit()
  o find_next_zero_bit_le()
and neither of these pass an @addr2, so the conversion is straightforward.

Signed-off-by: Valentin Schneider <vschneid@xxxxxxxxxx>
---
 include/linux/find.h | 44 ++++++++++++++++++++++++++++++++++++++------
 lib/find_bit.c       | 23 ++++++++++++-----------
 2 files changed, 50 insertions(+), 17 deletions(-)

diff --git a/include/linux/find.h b/include/linux/find.h
index 424ef67d4a42..920597de4e62 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -10,7 +10,8 @@
 
 extern unsigned long _find_next_bit(const unsigned long *addr1,
 		const unsigned long *addr2, unsigned long nbits,
-		unsigned long start, unsigned long invert, unsigned long le);
+		unsigned long start, unsigned long invert1, unsigned long invert2,
+		unsigned long le);
 extern unsigned long _find_first_bit(const unsigned long *addr, unsigned long size);
 extern unsigned long _find_first_and_bit(const unsigned long *addr1,
 					 const unsigned long *addr2, unsigned long size);
@@ -41,7 +42,7 @@ unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
 		return val ? __ffs(val) : size;
 	}
 
-	return _find_next_bit(addr, NULL, size, offset, 0UL, 0);
+	return _find_next_bit(addr, NULL, size, offset, 0UL, 0UL, 0);
 }
 #endif
 
@@ -71,7 +72,38 @@ unsigned long find_next_and_bit(const unsigned long *addr1,
 		return val ? __ffs(val) : size;
 	}
 
-	return _find_next_bit(addr1, addr2, size, offset, 0UL, 0);
+	return _find_next_bit(addr1, addr2, size, offset, 0UL, 0UL, 0);
+}
+#endif
+
+#ifndef find_next_andnot_bit
+/**
+ * find_next_andnot_bit - find the next set bit in one memory region
+ *                        but not in the other
+ * @addr1: The first address to base the search on
+ * @addr2: The second address to base the search on
+ * @size: The bitmap size in bits
+ * @offset: The bitnumber to start searching at
+ *
+ * Returns the bit number for the next set bit
+ * If no bits are set, returns @size.
+ */
+static inline
+unsigned long find_next_andnot_bit(const unsigned long *addr1,
+		const unsigned long *addr2, unsigned long size,
+		unsigned long offset)
+{
+	if (small_const_nbits(size)) {
+		unsigned long val;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = *addr1 & ~*addr2 & GENMASK(size - 1, offset);
+		return val ? __ffs(val) : size;
+	}
+
+	return _find_next_bit(addr1, addr2, size, offset, 0UL, ~0UL, 0);
 }
 #endif
 
@@ -99,7 +131,7 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
 		return val == ~0UL ? size : ffz(val);
 	}
 
-	return _find_next_bit(addr, NULL, size, offset, ~0UL, 0);
+	return _find_next_bit(addr, NULL, size, offset, ~0UL, 0UL, 0);
 }
 #endif
 
@@ -247,7 +279,7 @@ unsigned long find_next_zero_bit_le(const void *addr, unsigned
 		return val == ~0UL ? size : ffz(val);
 	}
 
-	return _find_next_bit(addr, NULL, size, offset, ~0UL, 1);
+	return _find_next_bit(addr, NULL, size, offset, ~0UL, 0UL, 1);
 }
 #endif
 
@@ -266,7 +298,7 @@ unsigned long find_next_bit_le(const void *addr, unsigned
 		return val ? __ffs(val) : size;
 	}
 
-	return _find_next_bit(addr, NULL, size, offset, 0UL, 1);
+	return _find_next_bit(addr, NULL, size, offset, 0UL, 0UL, 1);
 }
 #endif
 
diff --git a/lib/find_bit.c b/lib/find_bit.c
index 1b8e4b2a9cba..c46b66d7d2b4 100644
--- a/lib/find_bit.c
+++ b/lib/find_bit.c
@@ -21,27 +21,29 @@
 
 #if !defined(find_next_bit) || !defined(find_next_zero_bit) ||			\
 	!defined(find_next_bit_le) || !defined(find_next_zero_bit_le) ||	\
-	!defined(find_next_and_bit)
+	!defined(find_next_and_bit) || !defined(find_next_andnot_bit)
 /*
  * This is a common helper function for find_next_bit, find_next_zero_bit, and
  * find_next_and_bit. The differences are:
- *  - The "invert" argument, which is XORed with each fetched word before
- *    searching it for one bits.
  *  - The optional "addr2", which is anded with "addr1" if present.
+ *  - The "invert" arguments, which are XORed with each fetched word (invert1
+ *    for words in addr1, invert2 for those in addr2) before searching it for
+ *    one bits.
  */
 unsigned long _find_next_bit(const unsigned long *addr1,
-		const unsigned long *addr2, unsigned long nbits,
-		unsigned long start, unsigned long invert, unsigned long le)
+			     const unsigned long *addr2,
+			     unsigned long nbits, unsigned long start,
+			     unsigned long invert1, unsigned long invert2,
+			     unsigned long le)
 {
 	unsigned long tmp, mask;
 
 	if (unlikely(start >= nbits))
 		return nbits;
 
-	tmp = addr1[start / BITS_PER_LONG];
+	tmp = addr1[start / BITS_PER_LONG] ^ invert1;
 	if (addr2)
-		tmp &= addr2[start / BITS_PER_LONG];
-	tmp ^= invert;
+		tmp &= addr2[start / BITS_PER_LONG] ^ invert2;
 
 	/* Handle 1st word. */
 	mask = BITMAP_FIRST_WORD_MASK(start);
@@ -57,10 +59,9 @@ unsigned long _find_next_bit(const unsigned long *addr1,
 		if (start >= nbits)
 			return nbits;
 
-		tmp = addr1[start / BITS_PER_LONG];
+		tmp = addr1[start / BITS_PER_LONG] ^ invert1;
 		if (addr2)
-			tmp &= addr2[start / BITS_PER_LONG];
-		tmp ^= invert;
+			tmp &= addr2[start / BITS_PER_LONG] ^ invert2;
 	}
 
 	if (le)
-- 
2.31.1