[Libre-soc-isa] [Bug 1061] New: change extsb/h/w definitions to scale input size with XLEN rather than convert from fixed sizes

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1061

            Bug ID: 1061
           Summary: change extsb/h/w definitions to scale input size with
                    XLEN rather than convert from fixed sizes
           Product: Libre-SOC's first SoC
           Version: unspecified
          Hardware: Other
                OS: Linux
            Status: CONFIRMED
          Severity: enhancement
          Priority: ---
         Component: Specification
          Assignee: lkcl at lkcl.net
          Reporter: programmerjake at gmail.com
                CC: libre-soc-isa at lists.libre-soc.org
   NLnet milestone: ---

https://libre-soc.org/irclog/%23libre-soc.2023-04-18.log.html#t2023-04-18T10:09:54
(fixed spelling)
> so, lkcl, what do you think of changing extsb/h/w to be:
> RA <- EXTSXL(RS, XLEN/N) for N = 8/4/2 respectively
> instead of: RA <- EXTSXL(RS, N) for N = 8/16/32 respectively?

this allows sign extending from 1/2/4-bit values while retaining the existing
ability to sign extend from 8/16/32-bit values, all that changes is which of
extsb/h/w you need to use for each case.

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