[Libre-soc-isa] [Bug 650] write rfc for OpenPower fpr <-> gpr moves/conversions

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Thu Jun 3 23:22:06 BST 2021


--- Comment #20 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
hmmm, given that the "standard" way of doing fp conversion is not
equal to how OpenPOWER does it, i think it would be highly illustrative
to also include c as well, in the appendix

i'm assuming there that c implements "standard" IEEE754.


        fctiwz 1,1
        addi 9,1,-16
        stfiwx 1,0,9
        lwz 3,-16(1)
        extsw 3,3
        .long 0
        .byte 0,9,0,0,0,0,0,0

which is still pretty awful.  5 instructions including a LD/ST, which
gets 2 other registers involved plus some local stack.

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