Re: [Qemu-devel] Mips 64 emulation not compiling

[Christian \"Eddie\" Dost]

The sparc64 popc works in O(lg(n)), the "optimized" code below work in 
O(n). Could be better to generalize the sparc64 code, like this:

static always_inline int ctpop32 (uint32_t val)
{
        uint32_t i;

        i = (val & 0x55555555) + ((val >>  1) & 0x55555555);
        i = (i   & 0x33333333) + ((i   >>  2) & 0x33333333);
        i = (i   & 0x0f0f0f0f) + ((i   >>  4) & 0x0f0f0f0f);
        i = (i   & 0x00ff00ff) + ((i   >>  8) & 0x00ff00ff);
        i = (i   & 0x0000ffff) + ((i   >> 16) & 0x0000ffff);

        return i;
}

For the 64 bit version see target-sparc/op_helper.c

Best regards,
Eddie

Blue Swirl wrote:
> On 10/27/07, J. Mayer <address@hidden> wrote:
> > I also got optimized versions of bit population count which could also
> > be shared:
> > static always_inline int ctpop32 (uint32_t val)
> > {
> >     int i;
> >
> >     for (i = 0; val != 0; i++)
> >         val = val ^ (val - 1);
> >
> >     return i;
> > }
> >
> > If you prefer, I can add those shared functions (ctz32, ctz64, cto32,
> > cto64, ctpop32, ctpop64) later, as they do not seem as widely used as
> > clxxx functions.
>
> This would be interesting for Sparc64. Could you compare your version
> to do_popc() in target-sparc/op_helper.c?

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