This is the mail archive of the libc-ports@sources.redhat.com mailing list for the libc-ports project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH 19/26] arm: Add optimized ffs for armv6t2


On 02/27/2013 07:51 AM, Måns Rullgård wrote:
> Richard Henderson <rth@twiddle.net> writes:
> 
>> +ENTRY(__ffs)
>> +	cmp	r0, #0
>> +	ittt	ne
>> +	rbitne	r0, r0
>> +	clzne	r0, r0
>> +	addne	r0, r0, #1
>> +	bx	lr
>> +END(__ffs)
> 
> Making the RBIT unconditional (bit-reverse of zero is still zero) is
> better since it reduces dependencies between instructions.  Depending on
> microarchitecture details, this might save a cycle.
> 

Fair enough.  Consider this change made for any next round.


r~


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]