Re: [Qemu-devel] [PATCH] bitops: unify bitops_flsl with host-utils.h, call it bitops_clzl

[Peter Maydell]

On 4 February 2013 18:26, Richard Henderson <address@hidden> wrote:
>  /**
> - * bitops_fls - find last (most-significant) set bit in a long word
> + * bitops_clzl - find last (most-significant) set bit in a long word

Should probably change the descriptive text to say "count leading
zeros"...

>   * @word: the word to search
>   *
>   * Undefined if no set bit exists, so code should check against 0 first.

Should we change this to match clz32()/clz64()/bitops_ctzl() in not
having an undefined-behaviour case?

>   */
> -static inline unsigned long bitops_flsl(unsigned long word)
> +static inline unsigned long bitops_clzl(unsigned long word)
>  {
> -       int num = BITS_PER_LONG - 1;
> -
> -#if LONG_MAX > 0x7FFFFFFF
> -       if (!(word & (~0ul << 32))) {
> -               num -= 32;
> -               word <<= 32;
> -       }
> +    /* Both this function and the gcc builtin are undefined at 0, whereas
> +       the host-utils functions return word-size at 0.  Thus we prefer the
> +       gcc builtin as the closer match.  */

I think we should just fix the inconsistency rather than
retaining several similarly-named functions which have differing
corner-case behaviour.

-- PMM