[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] x86: replace a few do_div() uses
On 12/01/2022 09:00, Jan Beulich wrote: > When the macro's "return value" is not used, the macro use can be > replaced by a simply division, avoiding some obfuscation. > > According to my observations, no change to generated code. > > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> I like this change in principle, but see below. do_div() needs to be deleted, because it's far too easy screw up. At a bare minimum, it should be replaced with a static inline that takes it's first parameter by pointer, because then at least every callsite reads correctly in terms of the C language. > --- a/xen/arch/x86/time.c > +++ b/xen/arch/x86/time.c > @@ -610,8 +610,7 @@ static uint64_t xen_timer_cpu_frequency( > struct vcpu_time_info *info = &this_cpu(vcpu_info)->time; > uint64_t freq; > > - freq = 1000000000ULL << 32; > - do_div(freq, info->tsc_to_system_mul); > + freq = (1000000000ULL << 32) / info->tsc_to_system_mul; > if ( info->tsc_shift < 0 ) > freq <<= -info->tsc_shift; do_div()'s output is consumed here. I don't think this hunk is safe to convert. ~Andrew
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