\[2 \cdot \tan^{-1} \left(\sqrt{\frac{1 - x}{1 + x}}\right)\]
Test:
arccos
Bits:
128 bits
Bits error versus x
Time: 3.9 s
Input Error: 0.0
Output Error: 0.0
Log: ⚲
Profile: 🕒
\(2 \cdot \tan^{-1} \left(\sqrt{\frac{1 - x}{1 + x}}\right)\)
  1. Started with
    \[2 \cdot \tan^{-1} \left(\sqrt{\frac{1 - x}{1 + x}}\right)\]
    0.0
  2. Removed slow pow expressions

Original test:


(lambda ((x default))
  #:name "arccos"
  (* 2 (atan (sqrt (/ (- 1 x) (+ 1 x))))))