Re: [tip:x86/asm] x86, bitops: Change bitops to be native operand size

Joe Perches
2013-11-12T02:54:48Z

On Mon, 2013-11-11 at 15:34 -0800, H. Peter Anvin wrote:
> On 11/10/2013 06:22 PM, Joe Perches wrote:
> >
> > Perhaps the current x86 bitops asm code is being conflated
> > with the ideal implementation?
> >
> Yes, by you.

Really? I don't think so.

How does the use of signed long for an index where
no negative values are possible or the use of a
negative int for BIT_MASK make sense?

> x86 has instructions that operate on signed bitindicies.

indices.

> It doesn't
> have instructions that operate on unsigned bitindicies. Unless someone
> is willing to do the work to prove that shift and mask is actually
> faster than using the hardware instructions (which I doubt, but it is
> always a possibility), that's what we have.

That doesn't mean x86 is the ideal implementation.