[PATCH] bitops: simplify generic bit finding functions

[Harvey Harrison]

No need for a sentinal if we explicitly catch the no bits/all bits set
cases, make it clear they are special cases returning size/BITS_PER_LONG.

Signed-off-by: Harvey Harrison <harvey.harrison@xxxxxxxxx>
---
 include/linux/bitops.h |   93 ++++++++++++++++++++----------------------------
 1 files changed, 39 insertions(+), 54 deletions(-)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 48bde60..d9eb58a 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -127,18 +127,17 @@ extern unsigned long __find_first_bit(const unsigned long *addr,
 static __always_inline unsigned long
 find_first_bit(const unsigned long *addr, unsigned long size)
 {
-	/* Avoid a function call if the bitmap size is a constant */
-	/* and not bigger than BITS_PER_LONG. */
-
-	/* insert a sentinel so that __ffs returns size if there */
-	/* are no set bits in the bitmap */
-	if (__builtin_constant_p(size) && (size < BITS_PER_LONG))
-		return __ffs((*addr) | (1ul << size));
-
-	/* the result of __ffs(0) is undefined, so it needs to be */
-	/* handled separately */
-	if (__builtin_constant_p(size) && (size == BITS_PER_LONG))
-		return ((*addr) == 0) ? BITS_PER_LONG : __ffs(*addr);
+	/*
+	 * Avoid a function call if the bitmap size is a constant and not
+	 * bigger than BITS_PER_LONG.  Ensure we return size if there are
+	 * no set bits.
+	 */
+	if (__builtin_constant_p(size) && (size <= BITS_PER_LONG)) {
+		if (*addr == 0)
+			return (size < BITS_PER_LONG) ? size : BITS_PER_LONG;
+		else
+			return __ffs(*addr);
+	}
 
 	/* size is not constant or too big */
 	return __find_first_bit(addr, size);
@@ -157,20 +156,17 @@ extern unsigned long __find_first_zero_bit(const unsigned long *addr,
 static __always_inline unsigned long
 find_first_zero_bit(const unsigned long *addr, unsigned long size)
 {
-	/* Avoid a function call if the bitmap size is a constant */
-	/* and not bigger than BITS_PER_LONG. */
-
-	/* insert a sentinel so that __ffs returns size if there */
-	/* are no set bits in the bitmap */
-	if (__builtin_constant_p(size) && (size < BITS_PER_LONG)) {
-		return __ffs(~(*addr) | (1ul << size));
+	/*
+	 * Avoid a function call if the bitmap size is a constant and not
+	 * bigger than BITS_PER_LONG.  Ensure we return size if all bits set.
+	 */
+	if (__builtin_constant_p(size) && (size <= BITS_PER_LONG)) {
+		if ((~(*addr)) == 0)
+			return (size < BITS_PER_LONG) ? size : BITS_PER_LONG;
+		else
+			return __ffs(~(*addr));
 	}
 
-	/* the result of __ffs(0) is undefined, so it needs to be */
-	/* handled separately */
-	if (__builtin_constant_p(size) && (size == BITS_PER_LONG))
-		return (~(*addr) == 0) ? BITS_PER_LONG : __ffs(~(*addr));
-
 	/* size is not constant or too big */
 	return __find_first_zero_bit(addr, size);
 }
@@ -192,22 +188,17 @@ find_next_bit(const unsigned long *addr, unsigned long size,
 {
 	unsigned long value;
 
-	/* Avoid a function call if the bitmap size is a constant */
-	/* and not bigger than BITS_PER_LONG. */
-
-	/* insert a sentinel so that __ffs returns size if there */
-	/* are no set bits in the bitmap */
-	if (__builtin_constant_p(size) && (size < BITS_PER_LONG)) {
+	/*
+	 * Avoid a function call if the bitmap size is a constant and not
+	 * bigger than BITS_PER_LONG.  Ensure we return size if there are
+	 * no set bits.
+	 */
+	if (__builtin_constant_p(size) && (size <= BITS_PER_LONG)) {
 		value = (*addr) & ((~0ul) << offset);
-		value |= (1ul << size);
-		return __ffs(value);
-	}
-
-	/* the result of __ffs(0) is undefined, so it needs to be */
-	/* handled separately */
-	if (__builtin_constant_p(size) && (size == BITS_PER_LONG)) {
-		value = (*addr) & ((~0ul) << offset);
-		return (value == 0) ? BITS_PER_LONG : __ffs(value);
+		if (value == 0)
+			return (size < BITS_PER_LONG) ? size : BITS_PER_LONG;
+		else
+			return __ffs(value);
 	}
 
 	/* size is not constant or too big */
@@ -229,22 +220,16 @@ find_next_zero_bit(const unsigned long *addr, unsigned long size,
 {
 	unsigned long value;
 
-	/* Avoid a function call if the bitmap size is a constant */
-	/* and not bigger than BITS_PER_LONG. */
-
-	/* insert a sentinel so that __ffs returns size if there */
-	/* are no set bits in the bitmap */
-	if (__builtin_constant_p(size) && (size < BITS_PER_LONG)) {
-		value = (~(*addr)) & ((~0ul) << offset);
-		value |= (1ul << size);
-		return __ffs(value);
-	}
-
-	/* the result of __ffs(0) is undefined, so it needs to be */
-	/* handled separately */
-	if (__builtin_constant_p(size) && (size == BITS_PER_LONG)) {
+	/*
+	 * Avoid a function call if the bitmap size is a constant and not
+	 * bigger than BITS_PER_LONG.  Ensure we return size if all bits set.
+	 */
+	if (__builtin_constant_p(size) && (size <= BITS_PER_LONG)) {
 		value = (~(*addr)) & ((~0ul) << offset);
-		return (value == 0) ? BITS_PER_LONG : __ffs(value);
+		if (value == 0)
+			return (size < BITS_PER_LONG) ? size : BITS_PER_LONG;
+		else
+			return __ffs(value);
 	}
 
 	/* size is not constant or too big */
-- 
1.5.5.1.270.g89765



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