Re: [power7-meissner] Vectorize simple math builtins

[Paolo Bonzini <bonzini at gnu dot org>]

> > 	vspltisw	v1,-1	; v1 = (0xFFFFFFFF, ...)
> > 	vxor	v2,v3,v4
> > 	vslw	v1,v1,v1	; v1 = v1<<  31 = (0x80000000, ...)
> > 	vand	v1,v1,v2	; v1 != 0 if sign bits of v3/v4 differ
> > 	vxor	v1,v1,v3	; v1 = v3 with v4's sign bits
> >
> > Maybe it's worthwhile making it available for Altivec too.
>
> Actually it is much simpler to load up a mask with every bit set except for the
> sign bit (or just the sign bit set), and then do a vsel (vector select) between
> the value with the sign bit and the value with the rest of the floating point
> value.

Yeah, that would be vspltisw+vslw+vsel.

Paolo