> On Feb 10, 2025, at 7:15 PM, Doug Moore <do...@freebsd.org> wrote:
>
> The branch stable/14 has been updated by dougm:
>
> URL:
> https://cgit.FreeBSD.org/src/commit/?id=7bcc7a0b88ccb5e1fe31de88ab9a17e46859318b
>
> commit 7bcc7a0b88ccb5e1fe31de88ab9a17e46859318b
> Author: Doug Moore <do...@freebsd.org>
> AuthorDate: 2024-09-27 23:43:07 +0000
> Commit: Doug Moore <do...@freebsd.org>
> CommitDate: 2025-02-10 10:30:05 +0000
>
> libkern: avoid local var in order_base_2()
>
> order_base_2(n) is implemented with a variable, which keeps it from
> being used at file scope. Implement it instead as ilog2(2*n-1), which
> produces a different result when 2*n overflows, which appears unlikely
> in practice.
>
> Reviewed by: bz
> Differential Revision: https://reviews.freebsd.org/D46826
>
> (cherry picked from commit b7cbf741d55468ba34305a14ac3acc1c286af034)
> ---
> sys/sys/libkern.h | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/sys/sys/libkern.h b/sys/sys/libkern.h
> index a10289d72dc7..835e5ffaf0b7 100644
> --- a/sys/sys/libkern.h
> +++ b/sys/sys/libkern.h
> @@ -229,10 +229,7 @@ ilog2_long_long(long long n)
>
> #define ilog2(n) (__builtin_constant_p(n) ? ilog2_const(n) :
> ilog2_var(n))
> #define rounddown_pow_of_two(n) ((__typeof(n))1 << ilog2(n))
> -#define order_base_2(n) ({ \
> - __typeof(n) _n = (n); \
This local var `_n` is within the scope of the macro `order_base_2`, it is
surrounded with
{} and is harmless, so it will not pollute the file scoped variables.
Am I reading the commit message wrong ?
Best regards,
Zhenlei
> - _n == 1 ? 0 : 1 + ilog2(_n - 1); \
> -})
> +#define order_base_2(n) ilog2(2*(n)-1)
> #define roundup_pow_of_two(n) ((__typeof(n))1 << order_base_2(n))
>
> #define bitcount64(x) __bitcount64((uint64_t)(x))
