\[\frac{-\left(f + n\right)}{f - n}\]
Test:
subtraction fraction
Bits:
128 bits
Bits error versus f
Bits error versus n
Time: 4.4 s
Input Error: 0.0
Output Error: 0.0
Log: ⚲
Profile: 🕒
\(\log_* (1 + (e^{\frac{-\left(f + n\right)}{f - n}} - 1)^*)\)
  1. Started with
    \[\frac{-\left(f + n\right)}{f - n}\]
    0.0
  2. Using strategy rm
    0.0
  3. Applied log1p-expm1-u to get
    \[\color{red}{\frac{-\left(f + n\right)}{f - n}} \leadsto \color{blue}{\log_* (1 + (e^{\frac{-\left(f + n\right)}{f - n}} - 1)^*)}\]
    0.0

Original test:


(lambda ((f default) (n default))
  #:name "subtraction fraction"
  (/ (- (+ f n)) (- f n)))