nisse at lysator.liu.se
Mon Jan 14 18:45:54 CET 2013
Torbjorn Granlund <tg at gmplib.org> writes:
> Note that there are two *parallel* recurrency paths, one over over cya
> and one over cyb. Pairwise adjacent umaal have a dependency, but that's
> of the benign, non-recurrent type.
I don't fully understand it, but at a closer look it appears that there
*are* indeed independent umaal operations.
E.g., the first two in the loop
umaal r4, cya, u1, v0
.. store and reload r4 ...
umaal r5, cyb, u1, v1
If we use registers like
d0: v0, v1
d1: u1, u1
d2: r4, r5
d3: cya, cyb
precisely the same operations could be done with neon instructions as
vmull.u32 q3, d0, d1
vaddl.u32 q4, d2, d3
vadd q4, q4, q3
Do you agree? It would be 4 cycles on a9, 3 on a15. And then there will
be some data movements needed as well.
Niels Möller. PGP-encrypted email is preferred. Keyid C0B98E26.
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