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Comment by perihelions | Hacker News Reader

CORDIC is pretty obsolete, AFAIK. Its advantage is that its hardware requirements are absolutely tiny: two (?) accumulator registers, and hardware adders and shift-ers—I think that's all. No multiplication needed, in particular. Very convenient if you're building things from discrete transistors, like the some of those earlier scientific calculators!

(Also has a nice property, apparently, that CORDIC-like routines exist for a bunch of special functions and they're very similar to each other. Does anyone have a good resource for learning the details of those algorithms? They sound elegant).

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CORDIC still is used in tiny microcontrollers (smaller than Cortex-M0) and in FPGAs when you are very resource-constrained. Restricting the domain and using Chebyshev/Remez is the way to go pretty much everywhere.

I just recently came across CORDIC in a fun read I just finished, 'Empire of the Sum', by Keith Houston. It's a history of calculators, and there's a chapter on the HP-35 which used CORDIC. The author goes into some details how it was used by that constrained device.

There are a lot of references given in the book including more details on CORDIC.

CORDIC doesn't make sense if multiplies have a similar cost to adds. If you have cheap multiplications then a successive approximation is faster. If multiplications are expensive relative to adds then CORDIC can still generally win. Basically this is only the case nowadays if you are doing ASICs or FPGAs.

I have used CORDIC to compute fixed-point log/exp with 64 bits of precision, mostly because I wanted to avoid having to implement (portable) 64x64->128 bit integer multiplication in C. It is probably still slower than doing that, but the code was really simple, and very accurate.

I think still used out of necessity when hw floating point not available (like fpgas)

Multiplication is pretty much needed in cordic! And is far from obsolete! It works perfectly fine, and dont have any of the problems said in the article.

It uses multiplication by powers of two, which is a floating-point bit shift.

CORDIC doesn't use multipliers. That's the whole appeal for low performance hardware since it's all shifts and adds. It can still be useful on more capable platforms when you want sin and cos in one operation since there is no extra cost.

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