Re: [Qemu-devel] [PATCH 2/7] target-ppc: Implement unsigned quadword left/right shift and unit tests

[David Gibson <david@gibson.dropbear.id.au>]

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On Sat, Dec 03, 2016 at 05:37:27PM -0800, Richard Henderson wrote:
> On 12/02/2016 09:00 PM, Jose Ricardo Ziviani wrote:
> > +++ b/include/qemu/host-utils.h
> > @@ -29,6 +29,33 @@
> >  #include "qemu/bswap.h"
> > 
> >  #ifdef CONFIG_INT128
> > +static inline void urshift(uint64_t *plow, uint64_t *phigh, uint32_t shift)
> > +{
> > +    __uint128_t val = ((__uint128_t)*phigh << 64) | *plow;
> > +    val >>= (shift & 127);
> > +    *phigh = val >> 64;
> > +    *plow = val & 0xffffffffffffffff;
> > +}
> > +
> > +static inline void ulshift(uint64_t *plow, uint64_t *phigh,
> > +                           uint32_t shift, bool *overflow)
> > +{
> > +    __uint128_t val = ((__uint128_t)*phigh << 64) | *plow;
> > +
> > +    if (shift == 0) {
> > +        return;
> > +    }
> > +
> > +    if (shift > 127 || (val >> (128 - (shift & 127))) != 0) {
> > +        *overflow = true;
> > +    }
> > +
> > +    val <<= (shift & 127);
> > +
> > +    *phigh = val >> 64;
> > +    *plow = val & 0xffffffffffffffff;
> > +}
> > +
> 
> This belongs in qemu/int128.h, not here.  And certainly not predicated on
> CONFIG_INT128.

Is there actually any advantage to the __uint128_t based versions over
the 64-bit versions?

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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