Source: https://austinhenley.com/blog/cosine.html

Analyses how cosine is computed and benchmarks against math.h.

Tries 3 different approaches:

- Taylor series (with k terms) which gets perfect accuracy vs wolfram alpha/math.h, but is much slower.
- Table lookup where you generate all values of cosine for multiples of 1e-k for some k between 0 and pi, and get the closest value (so for e.g., precision 0.1, you’d get same result for 0.15, 0.16, 0.199).
- Finally, the best result comes from linear interpolation between subsequent lookups (0.15 would be (0.1+0.2)/2).

Neat. This last one is faster and as accurate as math.h, except it takes up a big chunk of space.