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Reply to @kenshirriff@oldbytes.space
Ken Shirriff@kenshirriff@oldbytes.space (2026-09-27 02:03:35)
Back in 1956, the Mach-2 B-58 Hustler had an analog navigation computer. It wasn't accurate enough, so they built a digital replacement. Sines and cosines are easy in analog, but required a new digital algorithm. They invented the CORDIC algorithm and built the 134-pound CORDIC computer.
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Ken Shirriff@kenshirriff@oldbytes.space (2026-09-27 02:03:52)
Usually, rotating a vector by an angle requires complicated math. But for some special angles, the calculation requires just shifts and adds, easy to do in hardware. The CORDIC algorithm breaks down an angle into special angles (using a table), does quick vector rotations, producing the trig answer.

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Ken Shirriff@kenshirriff@oldbytes.space (2026-09-27 02:04:21)
CORDIC became popular, especially in scientific calculators. The 8087 chip uses CORDIC, but goes further, also using a polynomial ratio to get more accuracy. The simple function 3x/(3-x^2) (blue) is surprisingly close to the tangent (red), better than a Taylor series (green).
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