[PATCH] bitops: simplify generic bit finding functions

Harvey Harrison
2008-04-27T20:19:53Z

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@gmail.com>
---
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