Home | Notifications | New Note | Local | Federated | Search | Logout

Note Detail

Ken Shirriff@kenshirriff@oldbytes.space (2026-09-27 02:02:02)
How do computers calculate complicated trig functions such as tangent? I took a look at Intel's 8087 floating-point chip under the microscope to find out. The chip combines two techniques to evaluate the tan function quickly and accurately: polynomials and an algorithm called CORDIC...
---Attachments---
image: https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/117/338/413/512/318/470/original/648a2154d87efd1b.png
---Reply---
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.
---Attachments---
image: https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/117/338/415/629/550/235/original/e1c96ddfaada2098.png
image: https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/117/338/417/160/755/990/original/adb0910344b86c17.png

---Replies---

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.