[Libre-soc-isa] [Bug 933] prefix-code (like huffman code) decode/encode instructions

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Sun Oct 2 18:57:03 BST 2022


--- Comment #42 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Jacob Lifshay from comment #41)

> it turns out that because prefix-codes are almost always (at least in both
> JPEG and DEFLATE) interleaved with plain binary bits or prefix-codes using
> different `tree` values, attempting to vectorize prefix-code decoding
> doesn't really work. even if it did, it wouldn't be much faster than a
> scalar pcdec. loop because of the scalar dependency chain between each
> pcdec. and the next/prev pcdec.

getting the instructions *into* a multi-issue pipeline is one priority,
the other is allowing high-performance implementations to perform
macro-op back-end ALUs, similar to the bigint wide ALUs

> that said, sv.pcdec./ff=ne should do what you're imagining afaict.


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