* Michael S. Tsirkin <m...@redhat.com> wrote:
> +static __always_inline int __constant_test_bit(long nr, const unsigned long
> *addr)
> +{
> + return ((1UL << (nr & (BITS_PER_LONG-1))) &
> + (addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
> +}
> +
> +static inline int __variable_test_bit(long nr, const unsigned long *addr)
> +{
> + int oldbit;
> +
> + asm volatile("bt %2,%1\n\t"
> + "sbb %0,%0"
> + : "=r" (oldbit)
> + : "m" (*addr), "Ir" (nr));
> +
> + return oldbit;
> +}
Color me confused, why use assembly for this at all?
Why not just use C for testing the bit (i.e. turn __constant_test_bit() into
__test_bit()) - that would also allow the compiler to propagate the result,
potentially more optimally than we can do it via SBB...
Thanks,
Ingo
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