[fpc-devel] x86_64.inc CompareByte

[Florian Klämpfl]

Am 16.10.2017 um 23:08 schrieb Markus Beth:
> On 16.10.2017 22:41, Florian Klämpfl wrote:
>>> P.S.: I am currently working on another version of CompareByte that might have a slightly higher
>>> latency for very small len but a higher throughput (2 cycles per iteration vs. 3 cycles on an Intel
>>> Arrandale CPU (Westmere microarchitecture)). But this would need some more testing and benchmarking.
>>> I can come up with it here again if this would be of any interest.
>>
>> Small lengths in terms of matching string or overall lengths?
> 
> It is small length in terms of matching string as there is some setup work before the loop.
> 
>> BTW: I would really like to see a PCMPSTR based implementation :)
> PCMPSTR is (at the moment) out of my scope. I thought PCMPSTR is part of SSE4.2. How would you deal
> with Intel core microarchitecture CPUs that don't have it?

Just set a flag at startup if it is supported and then branch on the flag. As the flag never
changes, branch prediction most likely will work very good.