Average Error: 37.4 → 0.4
Time: 7.6s
Precision: binary64
\[\sin \left(x + \varepsilon\right) - \sin x \]
↓
\[\mathsf{fma}\left(\cos \varepsilon - 1, \sin x, \sin \varepsilon \cdot \cos x\right) \]
\sin \left(x + \varepsilon\right) - \sin x
↓
\mathsf{fma}\left(\cos \varepsilon - 1, \sin x, \sin \varepsilon \cdot \cos x\right)

(FPCore (x eps) :precision binary64 (- (sin (+ x eps)) (sin x)))
↓
(FPCore (x eps)
 :precision binary64
 (fma (- (cos eps) 1.0) (sin x) (* (sin eps) (cos x))))
double code(double x, double eps) {
	return sin(x + eps) - sin(x);
}
↓
double code(double x, double eps) {
	return fma((cos(eps) - 1.0), sin(x), (sin(eps) * cos(x)));
}

Error

Bits error versus x

Bits error versus eps

Target

Original37.4
Target14.8
Herbie0.4
\[2 \cdot \left(\cos \left(x + \frac{\varepsilon}{2}\right) \cdot \sin \left(\frac{\varepsilon}{2}\right)\right) \]

Derivation

  1. Initial program 37.4

    \[\sin \left(x + \varepsilon\right) - \sin x \]

  2. Applied sin-sum_binary6422.5

    \[\leadsto \color{blue}{\left(\sin x \cdot \cos \varepsilon + \cos x \cdot \sin \varepsilon\right)} - \sin x \]

  3. Taylor expanded in x around inf 22.5

    \[\leadsto \color{blue}{\left(\cos x \cdot \sin \varepsilon + \cos \varepsilon \cdot \sin x\right) - \sin x} \]

  4. Simplified0.4

    \[\leadsto \color{blue}{\mathsf{fma}\left(\sin \varepsilon, \cos x, \sin x \cdot \left(\cos \varepsilon + -1\right)\right)} \]

  5. Taylor expanded in eps around inf 22.5

    \[\leadsto \color{blue}{\left(\cos \varepsilon \cdot \sin x + \sin \varepsilon \cdot \cos x\right) - \sin x} \]

  6. Simplified0.4

    \[\leadsto \color{blue}{\mathsf{fma}\left(\cos \varepsilon - 1, \sin x, \cos x \cdot \sin \varepsilon\right)} \]

  7. Taylor expanded in x around inf 0.4

    \[\leadsto \mathsf{fma}\left(\cos \varepsilon - 1, \sin x, \color{blue}{\sin \varepsilon \cdot \cos x}\right) \]

  8. Final simplification0.4

    \[\leadsto \mathsf{fma}\left(\cos \varepsilon - 1, \sin x, \sin \varepsilon \cdot \cos x\right) \]

Reproduce

herbie shell --seed 2022094 
(FPCore (x eps)
  :name "2sin (example 3.3)"
  :precision binary64

  :herbie-target
  (* 2.0 (* (cos (+ x (/ eps 2.0))) (sin (/ eps 2.0))))

  (- (sin (+ x eps)) (sin x)))