Average Error: 0.2 → 0.0
Time: 2.6s
Precision: 64
\[\frac{4 \cdot \left(\left(x - y\right) - z \cdot 0.5\right)}{z}\]
↓
\[\mathsf{fma}\left(4, \frac{x}{z}, -\mathsf{fma}\left(4, \frac{y}{z}, 2\right)\right)\]
\frac{4 \cdot \left(\left(x - y\right) - z \cdot 0.5\right)}{z}
↓
\mathsf{fma}\left(4, \frac{x}{z}, -\mathsf{fma}\left(4, \frac{y}{z}, 2\right)\right)
double f(double x, double y, double z) {
        double r904262 = 4.0;
        double r904263 = x;
        double r904264 = y;
        double r904265 = r904263 - r904264;
        double r904266 = z;
        double r904267 = 0.5;
        double r904268 = r904266 * r904267;
        double r904269 = r904265 - r904268;
        double r904270 = r904262 * r904269;
        double r904271 = r904270 / r904266;
        return r904271;
}
↓
double f(double x, double y, double z) {
        double r904272 = 4.0;
        double r904273 = x;
        double r904274 = z;
        double r904275 = r904273 / r904274;
        double r904276 = y;
        double r904277 = r904276 / r904274;
        double r904278 = 2.0;
        double r904279 = fma(r904272, r904277, r904278);
        double r904280 = -r904279;
        double r904281 = fma(r904272, r904275, r904280);
        return r904281;
}

Error

Bits error versus x

Bits error versus y

Bits error versus z

Target

Original0.2
Target0.0
Herbie0.0
\[4 \cdot \frac{x}{z} - \left(2 + 4 \cdot \frac{y}{z}\right)\]

Derivation

  1. Initial program 0.2

    \[\frac{4 \cdot \left(\left(x - y\right) - z \cdot 0.5\right)}{z}\]

  2. Simplified0.2

    \[\leadsto \color{blue}{\frac{4}{z} \cdot \left(x - \mathsf{fma}\left(0.5, z, y\right)\right)}\]

  3. Taylor expanded around 0 0.0

    \[\leadsto \color{blue}{4 \cdot \frac{x}{z} - \left(4 \cdot \frac{y}{z} + 2\right)}\]

  4. Simplified0.0

    \[\leadsto \color{blue}{\mathsf{fma}\left(4, \frac{x}{z}, -\mathsf{fma}\left(4, \frac{y}{z}, 2\right)\right)}\]

  5. Final simplification0.0

    \[\leadsto \mathsf{fma}\left(4, \frac{x}{z}, -\mathsf{fma}\left(4, \frac{y}{z}, 2\right)\right)\]

Reproduce

herbie shell --seed 2020035 +o rules:numerics
(FPCore (x y z)
  :name "Data.Array.Repa.Algorithms.ColorRamp:rampColorHotToCold from repa-algorithms-3.4.0.1, B"
  :precision binary64

  :herbie-target
  (- (* 4 (/ x z)) (+ 2 (* 4 (/ y z))))

  (/ (* 4 (- (- x y) (* z 0.5))) z))