Average Error: 0.1 → 0
Time: 4.2s
Precision: 64
\[x + \frac{x - y}{2}\]
↓
\[\mathsf{fma}\left(1.5, x, -y \cdot 0.5\right)\]
x + \frac{x - y}{2}
↓
\mathsf{fma}\left(1.5, x, -y \cdot 0.5\right)
double f(double x, double y) {
        double r625889 = x;
        double r625890 = y;
        double r625891 = r625889 - r625890;
        double r625892 = 2.0;
        double r625893 = r625891 / r625892;
        double r625894 = r625889 + r625893;
        return r625894;
}
↓
double f(double x, double y) {
        double r625895 = 1.5;
        double r625896 = x;
        double r625897 = y;
        double r625898 = 0.5;
        double r625899 = r625897 * r625898;
        double r625900 = -r625899;
        double r625901 = fma(r625895, r625896, r625900);
        return r625901;
}

Error

Bits error versus x

Bits error versus y

Target

Original0.1
Target0.1
Herbie0
\[1.5 \cdot x - 0.5 \cdot y\]

Derivation

  1. Initial program 0.1

    \[x + \frac{x - y}{2}\]

  2. Taylor expanded around 0 0.1

    \[\leadsto \color{blue}{1.5 \cdot x - 0.5 \cdot y}\]
  3. Using strategy rm

  4. Applied fma-neg0

    \[\leadsto \color{blue}{\mathsf{fma}\left(1.5, x, -0.5 \cdot y\right)}\]

  5. Simplified0

    \[\leadsto \mathsf{fma}\left(1.5, x, \color{blue}{-y \cdot 0.5}\right)\]

  6. Final simplification0

    \[\leadsto \mathsf{fma}\left(1.5, x, -y \cdot 0.5\right)\]

Reproduce

herbie shell --seed 2020047 +o rules:numerics
(FPCore (x y)
  :name "Graphics.Rendering.Chart.Axis.Types:hBufferRect from Chart-1.5.3"
  :precision binary64

  :herbie-target
  (- (* 1.5 x) (* 0.5 y))

  (+ x (/ (- x y) 2)))