[Libre-soc-isa] [Bug 1061] 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

--- Comment #3 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Jacob Lifshay from comment #2)
> note 1-bit to 8-bit sign extension is particularly useful for generating
> traditional simd masks (generally used in code not specifically designed for
> SVP64) where elements are either -1 or 0

e.g. code to generate 32-bit traditional simd masks (possibly faster than
shifting):

sv.extsb/elwid=8/subvl=4 *r3, *r3 # sign extend lsb but of each byte
sv.extsh/elwid=32 *r3, *r3 # sign extend least significant byte of each 32-bit
word to full word

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