[jasomill]

For more general algorithms along these lines, see exercises 25–28 in section 1.2.2 of Knuth[1] (and note that the printed solution to exercise 28 in early printings has an error[2]).

[1] D.E. Knuth, The art of computer programming. Vol. 1, third edition, Addison-Wesley, Reading, MA, 1997.

[2] https://www.werkema.com/2021/10/14/my-knuth-check/

[somat]

That knuth check story was pretty great. it reminded me of when I had to write pow() from scratch many years ago. However mine was not optimized in any way, and was a very sluggish naive implementation of an algorithm I found in the nist mathematical function library.

I was young and worked night shifts feeding tapes to a ibm mainframe, in the down time I would amuse myself by reading the ibm manuals laying around and writing scripts on the operator console, some useful and some not so much.

One of my more useless scripts was a sort terminal characters drawing routine, I wanted to draw lines at a specific angle which would require sin(), cos(), however, the scripting language used had no included trig functions. So I looked it up. and smuggled in a printout of the nist reference sin function. At which point I found, to my dismay, there also was no floating point power function. So the next night I smuggled in the printout for that one as well. And now, armed with a highly questionable implementation of sin(), cos(), pow() I could finally draw the hands for my stupid analog clock screensaver on the 3270 terminal. Honestly probably the highlight of my time there, but I was too scared to let anyone know about that script, didn't want them to think I had too much downtime.

https://dlmf.nist.gov/6.6