[libre-riscv-dev] [isa-dev] Re: FP transcendentals (trigonometry, root/exp/log) proposal
MitchAlsup at aol.com
Tue Aug 13 22:38:21 BST 2019
On Tuesday, August 13, 2019 at 4:05:30 PM UTC-5, lkcl wrote:
> On Tuesday, August 13, 2019 at 11:40:39 PM UTC+8, MitchAlsup wrote:
> > My actual implementation folds ATAN into ATAN2 and changes the last 2
> lines into::
> Thx Mitch have made a note so it's not lost in list noise.
> Also appreciate the microcode suggestions, have to give that some serious
> thought, whether to do something truly microcode-like or whether to do just
> a mini SRAM that contains subroutines that reprogrammable RISCV opcodes can
> Much lower level may prove more useful, micro code operations to do FP
> prenormalisation, post normalisation etc. all at expanded bitwidths.
The "KIND" of microcode I suggest is the kind where the Calculation Unit is
microcoded and the data path it sits on remains <whatever it was>.
Microcoding the main F/D/E part of the pipeline is strongly discouraged.
Think of microcode as if it were a sequencer, just express that sequencer
in such a way that the synthesizer can implement it with a table, with just
gates, or with some kind of ROM. Then you don't have to decide if it is
microcoded (or not) the synthesizer carries the load.
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