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SubjectRe: Kernel checksum routime (>=5)x86 optimization
On Tue, May 18, 1999 at 07:22:24AM +0200, Jamie Lokier wrote:
> Kurt Garloff wrote:
> > Well, I hacked a test. It seems my theory fails. Can someone explain, why
> > the PPro does not perform better using two regs?
>
> Because each instruction still depends on the previous one:
> `adcl' means to use the carry flag from the previous instruction.

Well, it does not in my test proggie.

By the way: Is it correct to use adcl in this piece of code???
Why do we want to add 1 instead of 1<<32 in case of overflow???

> For instructions this simple the integer units are probably faster than
> the instruction decoder anyway.

That might be the reason, yes.
it might also be that only one load can be executed per cycle.

> You might get better results with the PIII's 128-bit SIMD instructions ;-)

--
Kurt Garloff <garloff@suse.de> SuSE GmbH, Nürnberg, FRG
Linux kernel development; SCSI driver: DC390 (tmscsim/AM53C974)
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