Re: [PATCH 4/6] xen/bitops: Introduce for_each_set_bit()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.06.2024 21:07, Andrew Cooper wrote:
> --- a/xen/include/xen/bitops.h
> +++ b/xen/include/xen/bitops.h
> @@ -56,6 +56,16 @@ static always_inline __pure unsigned int ffs64(uint64_t x)
>          return !x || (uint32_t)x ? ffs(x) : ffs(x >> 32) + 32;
>  }
>  
> +/*
> + * A type-generic ffs() which picks the appropriate ffs{,l,64}() based on 
> it's
> + * argument.
> + */
> +#define ffs_g(x)                                        \
> +    sizeof(x) <= sizeof(int) ? ffs(x) :                 \
> +        sizeof(x) <= sizeof(long) ? ffsl(x) :           \
> +        sizeof(x) <= sizeof(uint64_t) ? ffs64(x) :      \
> +        ({ BUILD_ERROR("ffs_g() Bad input type"); 0; })

I guess the lack of parentheses around the entire construct might be the
reason for the problems you're seeing, as that ...

> @@ -92,6 +102,20 @@ static always_inline __pure unsigned int fls64(uint64_t x)
>      }
>  }
>  
> +/*
> + * for_each_set_bit() - Iterate over all set bits in a scalar value.
> + *
> + * @iter An iterator name.  Scoped is within the loop only.
> + * @val  A scalar value to iterate over.
> + *
> + * A copy of @val is taken internally.
> + */
> +#define for_each_set_bit(iter, val)                     \
> +    for ( typeof(val) __v = (val); __v; )               \
> +        for ( unsigned int (iter);                      \
> +              __v && ((iter) = ffs_g(__v) - 1, true);   \

... affects what effect the "- 1" here has.

Jan