Average Error: 0.1 → 0.0
Time: 3.8s
Precision: 64
\[\frac{x + y}{y + y}\]
↓
\[\mathsf{fma}\left(\frac{x}{y}, \frac{1}{2}, \frac{1}{2}\right)\]
\frac{x + y}{y + y}
↓
\mathsf{fma}\left(\frac{x}{y}, \frac{1}{2}, \frac{1}{2}\right)
double f(double x, double y) {
        double r33057638 = x;
        double r33057639 = y;
        double r33057640 = r33057638 + r33057639;
        double r33057641 = r33057639 + r33057639;
        double r33057642 = r33057640 / r33057641;
        return r33057642;
}
↓
double f(double x, double y) {
        double r33057643 = x;
        double r33057644 = y;
        double r33057645 = r33057643 / r33057644;
        double r33057646 = 0.5;
        double r33057647 = fma(r33057645, r33057646, r33057646);
        return r33057647;
}

Error

Bits error versus x

Bits error versus y

Target

Original0.1
Target0.0
Herbie0.0
\[0.5 \cdot \frac{x}{y} + 0.5\]

Derivation

  1. Initial program 0.1

    \[\frac{x + y}{y + y}\]

  2. Taylor expanded around 0 0.0

    \[\leadsto \color{blue}{\frac{1}{2} \cdot \frac{x}{y} + \frac{1}{2}}\]

  3. Simplified0.0

    \[\leadsto \color{blue}{\mathsf{fma}\left(\frac{x}{y}, \frac{1}{2}, \frac{1}{2}\right)}\]

  4. Final simplification0.0

    \[\leadsto \mathsf{fma}\left(\frac{x}{y}, \frac{1}{2}, \frac{1}{2}\right)\]

Reproduce

herbie shell --seed 2019169 +o rules:numerics
(FPCore (x y)
  :name "Data.Random.Distribution.T:$ccdf from random-fu-0.2.6.2"

  :herbie-target
  (+ (* 0.5 (/ x y)) 0.5)

  (/ (+ x y) (+ y y)))