[Libre-soc-isa] [Bug 817] Big Integer Math (sv.adde, sv.subfe, sv.madded, 128 by 64-bit -> 64-bit div/rem, maybe more...)

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=817

Luke Kenneth Casson Leighton <lkcl at lkcl.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://bugs.libre-soc.org/
                   |                            |show_bug.cgi?id=555

--- Comment #39 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
just realised that another variant of madded, call it say maddd, could be
used for high accuracy dotproduct (bug #555).

it would be:

    prod[0:127] = (RA) * (RB)
    sum[0:127] = (RC || [0]*64) + prod
    RT <- sum[64:127]
    RS <- sum[0:63] # RS is either RC or RT+VL

but the question is: is it worth doing in the integer space?
in FP, using 2 regs to store the intermediate result (FP128),
yes.  but integer? honestly i have no idea

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