[libre-riscv-dev] [Bug 208] implement CORDIC in a general way sufficient to do transcendentals

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=208

--- Comment #20 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #19)
> btw i don't recommend trying multiplying or dividing either the input
> or the output by pi inside the FP CORDIC code. we can use micro-coding for
> that (and in the unit tests do the divide and/or multiply using import math
> or import bigfloat).
> 
> so let us assume that we're implementing cospi and sinpi, here, *NOT*
> actual cos or actual sin, ok?

That will allow us to have a much more accurate cospi and sinpi because we
don't need multiple conversions. Also, since cospi and sinpi have a period of 2
which is a power of 2, it is super easy to do range reduction -- just some bit
masking.

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