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Re: [PATCH 20/26] arm: Implement armv6t2 optimized strlen
On 02/27/2013 09:12 AM, Måns Rullgård wrote:
> Richard Henderson <email@example.com> writes:
>> + @ Loop searching for EOS or C, 8 bytes at a time.
> This comment seems to be for strchr().
Whoops. As you can imagine there's some amount of cut and paste here. ;-)
> Subtracting the values (with UQSUB8) from 1 instead would result in a 0
> result any non-zero input and a 1 for "found", i.e. the inverse of what
> you have here. Testing for a match anywhere in the double-word then
> becomes a single ORRS instruction. Unless I'm making some stupid mistake.
Yes, this works. And a good idea for improvement.
> This code could be made to work for any ARMv6 by (conditionally)
> replacing the MOVW/MOVT with some equivalent and the RBIT by REV. REV
> works since only the lsb in each byte can be set, so the result of CLZ
> will simply be 7 more than we want, and the 3 low-order bits are shifted
> out anyway.
Ah, I'd mis-read the document the first time round and thought uqadd8 was an
armv6t2 instruction. I'll rearrange all these so that armv6 can benefit.
Which makes patch 3 once again useful... ;-)