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Re: [PATCH 19/26] arm: Add optimized ffs for armv6t2
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.
--
Måns Rullgård
mans@mansr.com