[Libre-soc-isa] [Bug 697] SVP64 Reduce Modes

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=697

--- Comment #4 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #3)
> there is already a "reverse gear" bit in SVP64

i don't think that does what we might need here...

reversed means it reduces like so (@ are adds;
this one is more efficient on arm):

0    1    2    3    4    5    6    7
|    |    |    |    |    |    |    |
@----|----|----|----/    |    |    |
|    @----|----|---------/    |    | distance=4
|    |    @----|--------------/    |
|    |    |    @-------------------/
|    |    |    |
@----|----/    | distance=2
|    @---------/
|    |
@----/ distance=1
|

the original (current SimpleV) reduce goes distance=1,2,4...

0    1    2    3    4    5    6    7
|    |    |    |    |    |    |    |
@----/    @----/    @----/    @----/ distance=1
|    .    |    .    |    .    |
@---------/    .    @---------/ distance=2
|    .    .    .    |
@-------------------/ distance=4
|

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