Average Error: 0.0 → 0.0
Time: 7.1s
Precision: 64
\[x.re \cdot y.re - x.im \cdot y.im\]
↓
\[\mathsf{fma}\left(x.re, y.re, -y.im \cdot x.im\right)\]
x.re \cdot y.re - x.im \cdot y.im
↓
\mathsf{fma}\left(x.re, y.re, -y.im \cdot x.im\right)
double f(double x_re, double x_im, double y_re, double y_im) {
        double r37971 = x_re;
        double r37972 = y_re;
        double r37973 = r37971 * r37972;
        double r37974 = x_im;
        double r37975 = y_im;
        double r37976 = r37974 * r37975;
        double r37977 = r37973 - r37976;
        return r37977;
}
↓
double f(double x_re, double x_im, double y_re, double y_im) {
        double r37978 = x_re;
        double r37979 = y_re;
        double r37980 = y_im;
        double r37981 = x_im;
        double r37982 = r37980 * r37981;
        double r37983 = -r37982;
        double r37984 = fma(r37978, r37979, r37983);
        return r37984;
}

Error

Bits error versus x.re

Bits error versus x.im

Bits error versus y.re

Bits error versus y.im

Derivation

  1. Initial program 0.0

    \[x.re \cdot y.re - x.im \cdot y.im\]
  2. Using strategy rm

  3. Applied fma-neg0.0

    \[\leadsto \color{blue}{\mathsf{fma}\left(x.re, y.re, -x.im \cdot y.im\right)}\]

  4. Simplified0.0

    \[\leadsto \mathsf{fma}\left(x.re, y.re, \color{blue}{-y.im \cdot x.im}\right)\]

  5. Final simplification0.0

    \[\leadsto \mathsf{fma}\left(x.re, y.re, -y.im \cdot x.im\right)\]

Reproduce

herbie shell --seed 2019326 +o rules:numerics
(FPCore (x.re x.im y.re y.im)
  :name "_multiplyComplex, real part"
  :precision binary64
  (- (* x.re y.re) (* x.im y.im)))