Falkner and Boettcher, Appendix B, 2

Average Error: 0.0 → 0.0

Time: 4.7s

Precision: binary64

Cost: 13632

Math

\[\left(\frac{\sqrt{2}}{4} \cdot \sqrt{1 - 3 \cdot \left(v \cdot v\right)}\right) \cdot \left(1 - v \cdot v\right) \]

↓

\[\sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)} \cdot \left(1 - v \cdot v\right) \]

FPCore

(FPCore (v)
 :precision binary64
 (* (* (/ (sqrt 2.0) 4.0) (sqrt (- 1.0 (* 3.0 (* v v))))) (- 1.0 (* v v))))

↓

(FPCore (v)
 :precision binary64
 (* (sqrt (* 0.125 (fma (* v v) -3.0 1.0))) (- 1.0 (* v v))))

C

double code(double v) {
	return ((sqrt(2.0) / 4.0) * sqrt((1.0 - (3.0 * (v * v))))) * (1.0 - (v * v));
}

↓

double code(double v) {
	return sqrt((0.125 * fma((v * v), -3.0, 1.0))) * (1.0 - (v * v));
}

Julia

function code(v)
	return Float64(Float64(Float64(sqrt(2.0) / 4.0) * sqrt(Float64(1.0 - Float64(3.0 * Float64(v * v))))) * Float64(1.0 - Float64(v * v)))
end

↓

function code(v)
	return Float64(sqrt(Float64(0.125 * fma(Float64(v * v), -3.0, 1.0))) * Float64(1.0 - Float64(v * v)))
end

Wolfram

code[v_] := N[(N[(N[(N[Sqrt[2.0], $MachinePrecision] / 4.0), $MachinePrecision] * N[Sqrt[N[(1.0 - N[(3.0 * N[(v * v), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]], $MachinePrecision]), $MachinePrecision] * N[(1.0 - N[(v * v), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]

↓

code[v_] := N[(N[Sqrt[N[(0.125 * N[(N[(v * v), $MachinePrecision] * -3.0 + 1.0), $MachinePrecision]), $MachinePrecision]], $MachinePrecision] * N[(1.0 - N[(v * v), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]

Derivation

1. Initial program 0.0

   \[\left(\frac{\sqrt{2}}{4} \cdot \sqrt{1 - 3 \cdot \left(v \cdot v\right)}\right) \cdot \left(1 - v \cdot v\right) \]

2. Simplified 0.0

   \[\leadsto \color{blue}{\frac{\sqrt{2}}{4} \cdot \left(\sqrt{1 - \left(3 \cdot v\right) \cdot v} \cdot \left(1 - v \cdot v\right)\right)} \]
   Proof

   [Start] 0.0	\[ \left(\frac{\sqrt{2}}{4} \cdot \sqrt{1 - 3 \cdot \left(v \cdot v\right)}\right) \cdot \left(1 - v \cdot v\right) \]
   associate-*l* [=>] 0.0	\[ \color{blue}{\frac{\sqrt{2}}{4} \cdot \left(\sqrt{1 - 3 \cdot \left(v \cdot v\right)} \cdot \left(1 - v \cdot v\right)\right)} \]
   associate-*r* [=>] 0.0	\[ \frac{\sqrt{2}}{4} \cdot \left(\sqrt{1 - \color{blue}{\left(3 \cdot v\right) \cdot v}} \cdot \left(1 - v \cdot v\right)\right) \]

3. Applied egg-rr 0.0

   \[\leadsto \color{blue}{\sqrt{0.125} \cdot \sqrt{1 - 3 \cdot \left(v \cdot v\right)} + \left(\sqrt{0.125} \cdot \sqrt{1 - 3 \cdot \left(v \cdot v\right)}\right) \cdot \left(v \cdot \left(-v\right)\right)} \]

4. Simplified 0.0

   \[\leadsto \color{blue}{\sqrt{0.125} \cdot \left(\sqrt{1 + v \cdot \left(v \cdot -3\right)} \cdot \left(1 - v \cdot v\right)\right)} \]
   Proof

   [Start] 0.0	\[ \sqrt{0.125} \cdot \sqrt{1 - 3 \cdot \left(v \cdot v\right)} + \left(\sqrt{0.125} \cdot \sqrt{1 - 3 \cdot \left(v \cdot v\right)}\right) \cdot \left(v \cdot \left(-v\right)\right) \]
   associate-*l* [=>] 0.0	\[ \sqrt{0.125} \cdot \sqrt{1 - 3 \cdot \left(v \cdot v\right)} + \color{blue}{\sqrt{0.125} \cdot \left(\sqrt{1 - 3 \cdot \left(v \cdot v\right)} \cdot \left(v \cdot \left(-v\right)\right)\right)} \]
   distribute-lft-out [=>] 0.0	\[ \color{blue}{\sqrt{0.125} \cdot \left(\sqrt{1 - 3 \cdot \left(v \cdot v\right)} + \sqrt{1 - 3 \cdot \left(v \cdot v\right)} \cdot \left(v \cdot \left(-v\right)\right)\right)} \]
   +-commutative [=>] 0.0	\[ \sqrt{0.125} \cdot \color{blue}{\left(\sqrt{1 - 3 \cdot \left(v \cdot v\right)} \cdot \left(v \cdot \left(-v\right)\right) + \sqrt{1 - 3 \cdot \left(v \cdot v\right)}\right)} \]
   +-commutative [<=] 0.0	\[ \sqrt{0.125} \cdot \color{blue}{\left(\sqrt{1 - 3 \cdot \left(v \cdot v\right)} + \sqrt{1 - 3 \cdot \left(v \cdot v\right)} \cdot \left(v \cdot \left(-v\right)\right)\right)} \]
   *-rgt-identity [<=] 0.0	\[ \sqrt{0.125} \cdot \left(\color{blue}{\sqrt{1 - 3 \cdot \left(v \cdot v\right)} \cdot 1} + \sqrt{1 - 3 \cdot \left(v \cdot v\right)} \cdot \left(v \cdot \left(-v\right)\right)\right) \]
   distribute-lft-in [<=] 0.0	\[ \sqrt{0.125} \cdot \color{blue}{\left(\sqrt{1 - 3 \cdot \left(v \cdot v\right)} \cdot \left(1 + v \cdot \left(-v\right)\right)\right)} \]
   cancel-sign-sub-inv [=>] 0.0	\[ \sqrt{0.125} \cdot \left(\sqrt{\color{blue}{1 + \left(-3\right) \cdot \left(v \cdot v\right)}} \cdot \left(1 + v \cdot \left(-v\right)\right)\right) \]
   metadata-eval [=>] 0.0	\[ \sqrt{0.125} \cdot \left(\sqrt{1 + \color{blue}{-3} \cdot \left(v \cdot v\right)} \cdot \left(1 + v \cdot \left(-v\right)\right)\right) \]
   *-commutative [<=] 0.0	\[ \sqrt{0.125} \cdot \left(\sqrt{1 + \color{blue}{\left(v \cdot v\right) \cdot -3}} \cdot \left(1 + v \cdot \left(-v\right)\right)\right) \]
   associate-*r* [<=] 0.0	\[ \sqrt{0.125} \cdot \left(\sqrt{1 + \color{blue}{v \cdot \left(v \cdot -3\right)}} \cdot \left(1 + v \cdot \left(-v\right)\right)\right) \]
   *-commutative [=>] 0.0	\[ \sqrt{0.125} \cdot \left(\sqrt{1 + v \cdot \left(v \cdot -3\right)} \cdot \left(1 + \color{blue}{\left(-v\right) \cdot v}\right)\right) \]

5. Applied egg-rr 0.0

   \[\leadsto \color{blue}{\sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)} + \left(-v \cdot v\right) \cdot \sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)}} \]

6. Simplified 0.0

   \[\leadsto \color{blue}{\sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)} \cdot \left(1 - v \cdot v\right)} \]
   Proof

   [Start] 0.0	\[ \sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)} + \left(-v \cdot v\right) \cdot \sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)} \]
   distribute-rgt1-in [=>] 0.0	\[ \color{blue}{\left(\left(-v \cdot v\right) + 1\right) \cdot \sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)}} \]
   +-commutative [<=] 0.0	\[ \color{blue}{\left(1 + \left(-v \cdot v\right)\right)} \cdot \sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)} \]
   sub-neg [<=] 0.0	\[ \color{blue}{\left(1 - v \cdot v\right)} \cdot \sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)} \]
   *-commutative [=>] 0.0	\[ \color{blue}{\sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)} \cdot \left(1 - v \cdot v\right)} \]

7. Final simplification 0.0

   \[\leadsto \sqrt{0.125 \cdot \mathsf{fma}\left(v \cdot v, -3, 1\right)} \cdot \left(1 - v \cdot v\right) \]

Alternatives

Alternative 1
Error	0.3
Cost	6976

\[\sqrt{2} \cdot \left(0.25 + \left(v \cdot v\right) \cdot -0.625\right) \]

Alternative 2
Error	0.7
Cost	6464

\[\sqrt{0.125} \]

Reproduce

herbie shell --seed 2023012 
(FPCore (v)
  :name "Falkner and Boettcher, Appendix B, 2"
  :precision binary64
  (* (* (/ (sqrt 2.0) 4.0) (sqrt (- 1.0 (* 3.0 (* v v))))) (- 1.0 (* v v))))