Re: kernel bitreverse function

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>   ((b * 0x80200802ull) & 0x0884422110ull) * 0x0101010101ull >> 32

>   ((b * 0x0802u & 0x22110u) | (b * 0x8020u & 0x88440u)) * 0x10101u >> 16

Maybe.  Do all machines NetBSD still cares about have fast-enough
multiply instructions?  Unless the multiply is unusually fast compared
to shift and mask instructions, I'd say it would likely have a hard
time beating

        b = ((b & 0x0f) << 4) | ((b >> 4) & 0x0f);
        b = ((b & 0x33) << 2) | ((b >> 2) & 0x33);
        b = ((b & 0x55) << 1) | ((b >> 1) & 0x55);

> It is also worth allowing for cpus that can have a hardware
> instruction (and then do it in 1 clock!)

Yes, I'd say this definitely should support MD implementations.

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