Interesting - pdf link here. I think their idea is to use quadratic interpolation and therefore have smaller lookup tables than needed for linear interpolation (with a second idea of minimising the length of the coefficients and a third idea of using squaring hardware to speed up the interpolation)

Moving slightly back towards integer arithmetic and plotting of a sine curve, there's an old trick due to Minsky which is a close approximation, and uses only add and shift. In fact, maybe not even a shift because a shift by 8 is just picking off a different byte:



At first this was drawing spirals, but it turned out I was using floating point division: it draws near-circles if integer division is used.


(Lots of other interesting tricks in the Hakmem memo.)

Fascinating. That is awesome info!

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65Org16:https://github.com/ElEctric-EyE/verilog-6502

Marvin's trick to draw circles was used as an example program in the Acorn Atom user manual: "Atomic theory and practice". An excellent book full little bits of useful code.

Nice! Code on Page 86 - picture on next page.

(I wish I'd been able to post those graphics as an ATALAN example... an exercise for the reader?)