Re: [Xen-devel] [PATCH v2] x86: reduce redundancy in tsc_[gs]et_info()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 06/05/14 14:56, Jan Beulich wrote:
>>>> On 06.05.14 at 15:49, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 06/05/14 14:29, Jan Beulich wrote:
>>>      case TSC_MODE_PVRDTSCP:
>>> -        d->arch.vtsc =  boot_cpu_has(X86_FEATURE_RDTSCP) &&
>>> -                        host_tsc_is_safe() ?  0 : 1;
>>> +        d->arch.vtsc = boot_cpu_has(X86_FEATURE_RDTSCP) &&
>>> +                       host_tsc_is_safe() ?  0 : 1;
>> Can this be reduced to boot_cpu_has(X86_FEATURE_RDTSCP) &&
>> !host_tsc_is_safe() ?
>>
>> I believe this is the correct way around with the precedence between &&
>> and ?!, but it is far from clear.  Alternatively, could some brackets be
>> introduced for clarity?
> No, ?: has lower precedence than all binary operators other than
> assignment ones and comma. But yes, this is ugly - I'll change it to

 /Sigh - I specifically looked the precedence up, then mentally got it
wrong given the linebreak.  It really is in need of some clarification.

>
> d->arch.vtsc = !(boot_cpu_has(X86_FEATURE_RDTSCP) && host_tsc_is_safe());

This was going to be my suggestion given the correct precedence.

~Andrew

>
> or, one character shorter,
>
> d->arch.vtsc = !boot_cpu_has(X86_FEATURE_RDTSCP) || !host_tsc_is_safe();
>
> (somehow I also managed to overlook the other double space in there).
>
> Jan
>


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