Messages in this thread Patch in this message | | | From | Qian Cai <> | Subject | [PATCH] bitmap: simplify GENMASK(size - 1, 0) lines | Date | Tue, 26 Oct 2021 10:41:08 -0400 |
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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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