[libre-riscv-dev] div pipe

Luke Kenneth Casson Leighton lkcl at lkcl.net
Mon Jul 20 02:38:28 BST 2020

On Monday, July 20, 2020, Jacob Lifshay <programmerjake at gmail.com> wrote:

> effectively what's happening is the code is treating the compare_?hs
> signals as if the binary value N means the fraction N/2^(3*fract_width)
> (essentially fixed-point numbers), so changing the bit width of N without
> adjusting the fract_width means there are too few integer bits and too many
> fractional bits.

ahh i remember.  that took a while to get right when connecting to fpdiv.

> additionally, some of the shifts and bit sliced will have
> to be adjusted to get the right bits.
> >
> > no reversion should be needed.
> >
> except that, last I checked DivPipeCore doesn't correctly do divisions when
> configured to only support UDivRem, since that's when it enables the broken
> code adjustments.

yuk.  hmm a way to "cheat" there: tell it that it can handle sqrt as well,
temporarily :)

that at least provides a functional codepath.  inefficient but functional.


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