[Libre-soc-isa] [Bug 966] create shift-and-add instruction

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=966

--- Comment #10 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Jacob Lifshay from comment #8)
> In the meeting today I pointed out that we probably also want shaddsw since
> C likes to use int for array indexing.
> 
> shaddsw:
> RT = RA + ((uint64_t)(int32_t)RB << (sh + 1))

the number of instructions being of some concern, this can be done
with extsw+shadd.  is there any compelling reason for an explicit
32bit shift-signed-add?  how much usage will it get in actual
compiled code?

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