From b2866e3ffe6efd307cc3cf52fb1f5676c6a5e1f1 Mon Sep 17 00:00:00 2001 From: Luke Kenneth Casson Leighton Date: Tue, 17 May 2022 11:13:17 +0100 Subject: [PATCH] badly-drawn version of diagram with grevlut added (temporary) --- openpower/sv/bitmanip/grev_gorc_design.mdwn | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/openpower/sv/bitmanip/grev_gorc_design.mdwn b/openpower/sv/bitmanip/grev_gorc_design.mdwn index 6816db81b..39b62430c 100644 --- a/openpower/sv/bitmanip/grev_gorc_design.mdwn +++ b/openpower/sv/bitmanip/grev_gorc_design.mdwn @@ -17,3 +17,10 @@ This gives us our final design: Notice how this still has an overall circuit latency that is essentially equivalent to grev's latency (or shift/rotate's latency). Also notice how this circuit allows specifying much more than just `grev` or `gorc` instructions. Layers of XOR gates can be added at the input and output, allowing it to function as a `gandc` instruction too, requiring a total of 6-bits of immediate (1 bit for inverting the input, 1 bit for inverting the output, 4 bits for the look-up-tables). We will also want versions of `grev` that have the shift amount be an immediate (needed for bitwise reverse and byte reversals and other similar instructions.) The immediate-shift-amount version can be specified to always do a `grev` (or maybe only `grev`/`gorc`) operation to save encoding space, since I'd guess it's much more common than any of the other immediate-shift variants. + +# Twin LUT4s + +gate-saving of the AND/OR (AOI) can be applied to grevlut. TODO, version +of diagram in SVG/DIA + + -- 2.30.2