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    Subject[PATCH 05/12] lib: extend the scope of small_const_nbits() macro
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    find_bit would also benefit from small_const_nbits() optimizations.
    The detailed comment is provided by Rasmus Villemoes.

    Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
    Signed-off-by: Yury Norov <yury.norov@gmail.com>
    Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
    ---
    include/asm-generic/bitsperlong.h | 12 ++++++++++++
    include/linux/bitmap.h | 8 --------
    2 files changed, 12 insertions(+), 8 deletions(-)

    diff --git a/include/asm-generic/bitsperlong.h b/include/asm-generic/bitsperlong.h
    index 3905c1c93dc2..1023e2a4bd37 100644
    --- a/include/asm-generic/bitsperlong.h
    +++ b/include/asm-generic/bitsperlong.h
    @@ -23,4 +23,16 @@
    #define BITS_PER_LONG_LONG 64
    #endif

    +/*
    + * small_const_nbits(n) is true precisely when it is known at compile-time
    + * that BITMAP_SIZE(n) is 1, i.e. 1 <= n <= BITS_PER_LONG. This allows
    + * various bit/bitmap APIs to provide a fast inline implementation. Bitmaps
    + * of size 0 are very rare, and a compile-time-known-size 0 is most likely
    + * a sign of error. They will be handled correctly by the bit/bitmap APIs,
    + * but using the out-of-line functions, so that the inline implementations
    + * can unconditionally dereference the pointer(s).
    + */
    +#define small_const_nbits(nbits) \
    + (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0)
    +
    #endif /* __ASM_GENERIC_BITS_PER_LONG */
    diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
    index 2cb1d7cfe8f9..a36cfcec4e77 100644
    --- a/include/linux/bitmap.h
    +++ b/include/linux/bitmap.h
    @@ -230,14 +230,6 @@ int bitmap_print_to_pagebuf(bool list, char *buf,
    #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
    #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))

    -/*
    - * The static inlines below do not handle constant nbits==0 correctly,
    - * so make such users (should any ever turn up) call the out-of-line
    - * versions.
    - */
    -#define small_const_nbits(nbits) \
    - (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0)
    -
    static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
    {
    unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
    --
    2.25.1
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