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Subject[PATCH] bitmap: simplify GENMASK(size - 1, 0) lines
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Since "size" is an "unsigned int", the rvalue "size - 1" will still be
"unsigned int" according to the C standard (3.2.1.5 Usual arithmetic
conversions). Therefore, GENMASK(size - 1, 0) will always return 0UL. Those
are also caught by GCC (W=2):

./include/linux/find.h: In function 'find_first_bit':
./include/linux/bits.h:25:22: warning: comparison of unsigned expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro 'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:25:3: note: in expansion of macro '__is_constexpr'
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^~~~~~~~~~~~~~
./include/linux/bits.h:38:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:119:31: note: in expansion of macro 'GENMASK'
119 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~
./include/linux/bits.h:25:34: warning: comparison of unsigned expression in '< 0' is always false [-Wtype-limits]
25 | __is_constexpr((l) > (h)), (l) > (h), 0)))
| ^
./include/linux/build_bug.h:16:62: note: in definition of macro 'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
./include/linux/bits.h:38:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
38 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
./include/linux/find.h:119:31: note: in expansion of macro 'GENMASK'
119 | unsigned long val = *addr & GENMASK(size - 1, 0);
| ^~~~~~~

Signed-off-by: Qian Cai <quic_qiancai@quicinc.com>
---
include/linux/find.h | 28 ++++++++--------------------
1 file changed, 8 insertions(+), 20 deletions(-)

diff --git a/include/linux/find.h b/include/linux/find.h
index 5bb6db213bcb..5ce2b17aea42 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -115,11 +115,8 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
static inline
unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
{
- if (small_const_nbits(size)) {
- unsigned long val = *addr & GENMASK(size - 1, 0);
-
- return val ? __ffs(val) : size;
- }
+ if (small_const_nbits(size))
+ return size;

return _find_first_bit(addr, size);
}
@@ -140,11 +137,8 @@ unsigned long find_first_and_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;
- }
+ if (small_const_nbits(size))
+ return size;

return _find_first_and_bit(addr1, addr2, size);
}
@@ -162,11 +156,8 @@ unsigned long find_first_and_bit(const unsigned long *addr1,
static inline
unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
{
- if (small_const_nbits(size)) {
- unsigned long val = *addr | ~GENMASK(size - 1, 0);
-
- return val == ~0UL ? size : ffz(val);
- }
+ if (small_const_nbits(size))
+ return size;

return _find_first_zero_bit(addr, size);
}
@@ -183,11 +174,8 @@ unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
static inline
unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
{
- if (small_const_nbits(size)) {
- unsigned long val = *addr & GENMASK(size - 1, 0);
-
- return val ? __fls(val) : size;
- }
+ if (small_const_nbits(size))
+ return size;

return _find_last_bit(addr, size);
}
--
2.30.2
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