[Libre-soc-isa] [Bug 973] New: expand svoffset so it can be used for dynamic vslideup/vslidedown; maybe also add insn for setting it from reg

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=973

            Bug ID: 973
           Summary: expand svoffset so it can be used for dynamic
                    vslideup/vslidedown; maybe also add insn for setting
                    it from reg
           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
            Blocks: 952
   NLnet milestone: ---

instruction for dynamically loading offset should have an option for setting
offset = RA >> 6 or -(RA >> 6) (negate after shift), needed for bigint shifts.
there should also be a plain offset = small_imm +- (RA) option.

summary:
v = (RA)
if sh6:
    v >>= 6  # RA counts bits to shift, we need 64-bit words
if negate:
    v = -v  # must happen after shift
offset = v + small_imm  # small_imm could be like 5-bit signed int
if shrink_vl:
    VL -= abs(v)  # needed to avoid reading/writing outside vector


Referenced Bugs:

https://bugs.libre-soc.org/show_bug.cgi?id=952
[Bug 952] NLnet 2022 OPF ISA WG Milestone 2022-08-051 (not approved)
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