Re: [PATCH 5/5] arch: x86: use sign_extend64() for sign extension

[George Spelvin]

> --- a/arch/x86/kernel/cpu/perf_event_msr.c
> +++ b/arch/x86/kernel/cpu/perf_event_msr.c
> @@ -163,10 +163,9 @@ again:
>  		goto again;
>  
>  	delta = now - prev;
> -	if (unlikely(event->hw.event_base == MSR_SMI_COUNT)) {
> -		delta <<= 32;
> -		delta >>= 32; /* sign extend */
> -	}
> +	if (unlikely(event->hw.event_base == MSR_SMI_COUNT))
> +		delta = sign_extend64(delta, 31);
> +
>  	local64_add(now - prev, &event->count);
>  }

GCC can figure it out wither way, but wouldn't

	delta = (s32)delta;

be simpler than either?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/