Re: [PATCH v2 05/19] host-utils: Add muldiv64_round_up

[Nicholas Piggin]

On Sat Sep 2, 2023 at 3:02 AM AEST, Richard Henderson wrote:
> On 9/1/23 04:51, Cédric Le Goater wrote:
> > Adding more reviewers since this patch is modifying a common service.
> > 
> > Thanks,
> > 
> > C.
> > 
> > 
> > On 8/8/23 06:19, Nicholas Piggin wrote:
> >> This will be used for converting time intervals in different base units
> >> to host units, for the purpose of scheduling timers to emulate target
> >> timers. Timers typically must not fire before their requested expiry
> >> time but may fire some time afterward, so rounding up is the right way
> >> to implement these.
> >>
> >> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> >> ---
> >>   include/qemu/host-utils.h | 21 ++++++++++++++++++++-
> >>   1 file changed, 20 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/include/qemu/host-utils.h b/include/qemu/host-utils.h
> >> index 011618373e..e2a50a567f 100644
> >> --- a/include/qemu/host-utils.h
> >> +++ b/include/qemu/host-utils.h
> >> @@ -56,6 +56,11 @@ static inline uint64_t muldiv64(uint64_t a, uint32_t b, 
> >> uint32_t c)
> >>       return (__int128_t)a * b / c;
> >>   }
> >> +static inline uint64_t muldiv64_round_up(uint64_t a, uint32_t b, uint32_t 
> >> c)
> >> +{
> >> +    return ((__int128_t)a * b + c - 1) / c;
> >> +}
> >> +
> >>   static inline uint64_t divu128(uint64_t *plow, uint64_t *phigh,
> >>                                  uint64_t divisor)
> >>   {
> >> @@ -83,7 +88,8 @@ void mulu64(uint64_t *plow, uint64_t *phigh, uint64_t a, 
> >> uint64_t b);
> >>   uint64_t divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor);
> >>   int64_t divs128(uint64_t *plow, int64_t *phigh, int64_t divisor);
> >> -static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)
> >> +static inline uint64_t __muldiv64(uint64_t a, uint32_t b, uint32_t c,
> >> +                                  bool round_up)
>
> Perhaps better avoiding the reserved name: muldiv64_internal?

Thanks, that would be okay. Or could be muldiv64_rounding?

>
> Otherwise,
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>
>
> r~
>
>
> >>   {
> >>       union {
> >>           uint64_t ll;
> >> @@ -99,12 +105,25 @@ static inline uint64_t muldiv64(uint64_t a, uint32_t 
> >> b, uint32_t c)
> >>       u.ll = a;
> >>       rl = (uint64_t)u.l.low * (uint64_t)b;
> >> +    if (round_up) {
> >> +        rl += c - 1;
> >> +    }
> >>       rh = (uint64_t)u.l.high * (uint64_t)b;
> >>       rh += (rl >> 32);
> >>       res.l.high = rh / c;
> >>       res.l.low = (((rh % c) << 32) + (rl & 0xffffffff)) / c;
> >>       return res.ll;
> >>   }
> >> +
> >> +static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)
> >> +{
> >> +    return __muldiv64(a, b, c, false);
> >> +}
> >> +
> >> +static inline uint64_t muldiv64_round_up(uint64_t a, uint32_t b, uint32_t 
> >> c)
> >> +{
> >> +    return __muldiv64(a, b, c, true);
> >> +}
> >>   #endif
> >>   /**
> > 
> >