Cubic critical, narrow range

Average Error: 28.6 → 5.0

Time: 6.8s

Precision: binary64

\[\left(\left(1.0536712127723509 \cdot 10^{-8} < a \land a < 94906265.62425156\right) \land \left(1.0536712127723509 \cdot 10^{-8} < b \land b < 94906265.62425156\right)\right) \land \left(1.0536712127723509 \cdot 10^{-8} < c \land c < 94906265.62425156\right)\]

Math

\[\frac{\left(-b\right) + \sqrt{b \cdot b - \left(3 \cdot a\right) \cdot c}}{3 \cdot a} \]

↓

\[\begin{array}{l} t_0 := \mathsf{fma}\left(a, c \cdot -3, b \cdot b\right)\\ \mathbf{if}\;\frac{\sqrt{b \cdot b - \left(3 \cdot a\right) \cdot c} - b}{3 \cdot a} \leq -14.767096848671262:\\ \;\;\;\;\left(\left(t_0 - b \cdot b\right) \cdot \frac{1}{b + \sqrt{t_0}}\right) \cdot \frac{0.3333333333333333}{a}\\ \mathbf{else}:\\ \;\;\;\;\mathsf{fma}\left(\frac{\left(a \cdot a\right) \cdot {c}^{3}}{{b}^{5}}, -0.5625, \mathsf{fma}\left(\frac{{a}^{3} \cdot {c}^{4}}{{b}^{7}}, -1.0546875, \mathsf{fma}\left(\frac{c \cdot \left(a \cdot c\right)}{{b}^{3}}, -0.375, -0.5 \cdot \frac{c}{b}\right)\right)\right)\\ \end{array} \]

FPCore

(FPCore (a b c)
 :precision binary64
 (/ (+ (- b) (sqrt (- (* b b) (* (* 3.0 a) c)))) (* 3.0 a)))

↓

(FPCore (a b c)
 :precision binary64
 (let* ((t_0 (fma a (* c -3.0) (* b b))))
   (if (<=
        (/ (- (sqrt (- (* b b) (* (* 3.0 a) c))) b) (* 3.0 a))
        -14.767096848671262)
     (* (* (- t_0 (* b b)) (/ 1.0 (+ b (sqrt t_0)))) (/ 0.3333333333333333 a))
     (fma
      (/ (* (* a a) (pow c 3.0)) (pow b 5.0))
      -0.5625
      (fma
       (/ (* (pow a 3.0) (pow c 4.0)) (pow b 7.0))
       -1.0546875
       (fma (/ (* c (* a c)) (pow b 3.0)) -0.375 (* -0.5 (/ c b))))))))

C

double code(double a, double b, double c) {
	return (-b + sqrt(((b * b) - ((3.0 * a) * c)))) / (3.0 * a);
}

↓

double code(double a, double b, double c) {
	double t_0 = fma(a, (c * -3.0), (b * b));
	double tmp;
	if (((sqrt(((b * b) - ((3.0 * a) * c))) - b) / (3.0 * a)) <= -14.767096848671262) {
		tmp = ((t_0 - (b * b)) * (1.0 / (b + sqrt(t_0)))) * (0.3333333333333333 / a);
	} else {
		tmp = fma((((a * a) * pow(c, 3.0)) / pow(b, 5.0)), -0.5625, fma(((pow(a, 3.0) * pow(c, 4.0)) / pow(b, 7.0)), -1.0546875, fma(((c * (a * c)) / pow(b, 3.0)), -0.375, (-0.5 * (c / b)))));
	}
	return tmp;
}

Julia

function code(a, b, c)
	return Float64(Float64(Float64(-b) + sqrt(Float64(Float64(b * b) - Float64(Float64(3.0 * a) * c)))) / Float64(3.0 * a))
end

↓

function code(a, b, c)
	t_0 = fma(a, Float64(c * -3.0), Float64(b * b))
	tmp = 0.0
	if (Float64(Float64(sqrt(Float64(Float64(b * b) - Float64(Float64(3.0 * a) * c))) - b) / Float64(3.0 * a)) <= -14.767096848671262)
		tmp = Float64(Float64(Float64(t_0 - Float64(b * b)) * Float64(1.0 / Float64(b + sqrt(t_0)))) * Float64(0.3333333333333333 / a));
	else
		tmp = fma(Float64(Float64(Float64(a * a) * (c ^ 3.0)) / (b ^ 5.0)), -0.5625, fma(Float64(Float64((a ^ 3.0) * (c ^ 4.0)) / (b ^ 7.0)), -1.0546875, fma(Float64(Float64(c * Float64(a * c)) / (b ^ 3.0)), -0.375, Float64(-0.5 * Float64(c / b)))));
	end
	return tmp
end

Wolfram

code[a_, b_, c_] := N[(N[((-b) + N[Sqrt[N[(N[(b * b), $MachinePrecision] - N[(N[(3.0 * a), $MachinePrecision] * c), $MachinePrecision]), $MachinePrecision]], $MachinePrecision]), $MachinePrecision] / N[(3.0 * a), $MachinePrecision]), $MachinePrecision]

↓

code[a_, b_, c_] := Block[{t$95$0 = N[(a * N[(c * -3.0), $MachinePrecision] + N[(b * b), $MachinePrecision]), $MachinePrecision]}, If[LessEqual[N[(N[(N[Sqrt[N[(N[(b * b), $MachinePrecision] - N[(N[(3.0 * a), $MachinePrecision] * c), $MachinePrecision]), $MachinePrecision]], $MachinePrecision] - b), $MachinePrecision] / N[(3.0 * a), $MachinePrecision]), $MachinePrecision], -14.767096848671262], N[(N[(N[(t$95$0 - N[(b * b), $MachinePrecision]), $MachinePrecision] * N[(1.0 / N[(b + N[Sqrt[t$95$0], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision] * N[(0.3333333333333333 / a), $MachinePrecision]), $MachinePrecision], N[(N[(N[(N[(a * a), $MachinePrecision] * N[Power[c, 3.0], $MachinePrecision]), $MachinePrecision] / N[Power[b, 5.0], $MachinePrecision]), $MachinePrecision] * -0.5625 + N[(N[(N[(N[Power[a, 3.0], $MachinePrecision] * N[Power[c, 4.0], $MachinePrecision]), $MachinePrecision] / N[Power[b, 7.0], $MachinePrecision]), $MachinePrecision] * -1.0546875 + N[(N[(N[(c * N[(a * c), $MachinePrecision]), $MachinePrecision] / N[Power[b, 3.0], $MachinePrecision]), $MachinePrecision] * -0.375 + N[(-0.5 * N[(c / b), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]]]

Error

Bits error versus a

Bits error versus b

Bits error versus c

Derivation

1. Split input into 2 regimes

2. if (/.f64 (+.f64 (neg.f64 b) (sqrt.f64 (-.f64 (*.f64 b b) (*.f64 (*.f64 3 a) c)))) (*.f64 3 a)) < -14.767096848671262

   1. Initial program 8.6

      \[\frac{\left(-b\right) + \sqrt{b \cdot b - \left(3 \cdot a\right) \cdot c}}{3 \cdot a} \]

   2. Simplified 8.6

      \[\leadsto \color{blue}{\left(\sqrt{\mathsf{fma}\left(a, c \cdot -3, b \cdot b\right)} - b\right) \cdot \frac{0.3333333333333333}{a}} \]

   3. Applied egg-rr 7.7

      \[\leadsto \color{blue}{\left(\left(\mathsf{fma}\left(a, c \cdot -3, b \cdot b\right) - b \cdot b\right) \cdot \frac{1}{b + \sqrt{\mathsf{fma}\left(a, c \cdot -3, b \cdot b\right)}}\right)} \cdot \frac{0.3333333333333333}{a} \]

   if -14.767096848671262 < (/.f64 (+.f64 (neg.f64 b) (sqrt.f64 (-.f64 (*.f64 b b) (*.f64 (*.f64 3 a) c)))) (*.f64 3 a))

   1. Initial program 30.4

      \[\frac{\left(-b\right) + \sqrt{b \cdot b - \left(3 \cdot a\right) \cdot c}}{3 \cdot a} \]

   2. Simplified 30.4

      \[\leadsto \color{blue}{\left(\sqrt{\mathsf{fma}\left(a, c \cdot -3, b \cdot b\right)} - b\right) \cdot \frac{0.3333333333333333}{a}} \]

   3. Taylor expanded in a around 0 4.7

      \[\leadsto \color{blue}{-\left(0.5625 \cdot \frac{{c}^{3} \cdot {a}^{2}}{{b}^{5}} + \left(1.0546875 \cdot \frac{{c}^{4} \cdot {a}^{3}}{{b}^{7}} + \left(0.375 \cdot \frac{{c}^{2} \cdot a}{{b}^{3}} + 0.5 \cdot \frac{c}{b}\right)\right)\right)} \]

   4. Simplified 4.7

      \[\leadsto \color{blue}{\mathsf{fma}\left(\frac{\left(a \cdot a\right) \cdot {c}^{3}}{{b}^{5}}, -0.5625, \mathsf{fma}\left(\frac{{a}^{3} \cdot {c}^{4}}{{b}^{7}}, -1.0546875, \mathsf{fma}\left(\frac{c \cdot \left(c \cdot a\right)}{{b}^{3}}, -0.375, -0.5 \cdot \frac{c}{b}\right)\right)\right)} \]
3. Recombined 2 regimes into one program.

4. Final simplification 5.0

   \[\leadsto \begin{array}{l} \mathbf{if}\;\frac{\sqrt{b \cdot b - \left(3 \cdot a\right) \cdot c} - b}{3 \cdot a} \leq -14.767096848671262:\\ \;\;\;\;\left(\left(\mathsf{fma}\left(a, c \cdot -3, b \cdot b\right) - b \cdot b\right) \cdot \frac{1}{b + \sqrt{\mathsf{fma}\left(a, c \cdot -3, b \cdot b\right)}}\right) \cdot \frac{0.3333333333333333}{a}\\ \mathbf{else}:\\ \;\;\;\;\mathsf{fma}\left(\frac{\left(a \cdot a\right) \cdot {c}^{3}}{{b}^{5}}, -0.5625, \mathsf{fma}\left(\frac{{a}^{3} \cdot {c}^{4}}{{b}^{7}}, -1.0546875, \mathsf{fma}\left(\frac{c \cdot \left(a \cdot c\right)}{{b}^{3}}, -0.375, -0.5 \cdot \frac{c}{b}\right)\right)\right)\\ \end{array} \]

Reproduce

herbie shell --seed 2022134 
(FPCore (a b c)
  :name "Cubic critical, narrow range"
  :precision binary64
  :pre (and (and (and (< 1.0536712127723509e-8 a) (< a 94906265.62425156)) (and (< 1.0536712127723509e-8 b) (< b 94906265.62425156))) (and (< 1.0536712127723509e-8 c) (< c 94906265.62425156)))
  (/ (+ (- b) (sqrt (- (* b b) (* (* 3.0 a) c)))) (* 3.0 a)))