On 08/29/2011 04:41 AM, Paolo Bonzini wrote: > The definition in OpenCL makes zero sense to me. For byte operands > it is custom-tailored after the SSE PMOVMSKB instruction, but there > is no PMOVMSKW/PMOVMSKD instruction so you would need very slow bit > shift operations before PMOVMSK. On the other hand, bit selection is > for example in Altivec.
Not PMOVMSKB, but the sse4.1 PBLENDVB. With that, we don't need funny shift operations for wider integer types, but only *because* the comparison produces -1, which means that the MSB of each byte is in fact set. Which means that the Perfect wording probably doesn't want to be specific to bit selection, but include bit selection (aka and-andn-or) as a valid implementation. r~
