quad2p (problem 3.2.1, positive)

Average Accuracy: 46.2% → 86.1%

Time: 17.4s

Precision: binary64

Cost: 7820

Math

\[\frac{\left(-b_2\right) + \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]

↓

\[\begin{array}{l} t_0 := \sqrt{b_2 \cdot b_2 - a \cdot c}\\ \mathbf{if}\;b_2 \leq -5 \cdot 10^{+92}:\\ \;\;\;\;-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}\\ \mathbf{elif}\;b_2 \leq 3.15 \cdot 10^{-102}:\\ \;\;\;\;\frac{t_0 - b_2}{a}\\ \mathbf{elif}\;b_2 \leq 2.4 \cdot 10^{+46}:\\ \;\;\;\;\frac{\frac{a \cdot \left(-c\right)}{b_2 + t_0}}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{b_2} \cdot -0.5\\ \end{array} \]

FPCore

(FPCore (a b_2 c)
 :precision binary64
 (/ (+ (- b_2) (sqrt (- (* b_2 b_2) (* a c)))) a))

↓

(FPCore (a b_2 c)
 :precision binary64
 (let* ((t_0 (sqrt (- (* b_2 b_2) (* a c)))))
   (if (<= b_2 -5e+92)
     (+ (* -2.0 (/ b_2 a)) (* 0.5 (/ c b_2)))
     (if (<= b_2 3.15e-102)
       (/ (- t_0 b_2) a)
       (if (<= b_2 2.4e+46)
         (/ (/ (* a (- c)) (+ b_2 t_0)) a)
         (* (/ c b_2) -0.5))))))

C

double code(double a, double b_2, double c) {
	return (-b_2 + sqrt(((b_2 * b_2) - (a * c)))) / a;
}

↓

double code(double a, double b_2, double c) {
	double t_0 = sqrt(((b_2 * b_2) - (a * c)));
	double tmp;
	if (b_2 <= -5e+92) {
		tmp = (-2.0 * (b_2 / a)) + (0.5 * (c / b_2));
	} else if (b_2 <= 3.15e-102) {
		tmp = (t_0 - b_2) / a;
	} else if (b_2 <= 2.4e+46) {
		tmp = ((a * -c) / (b_2 + t_0)) / a;
	} else {
		tmp = (c / b_2) * -0.5;
	}
	return tmp;
}

Fortran

real(8) function code(a, b_2, c)
    real(8), intent (in) :: a
    real(8), intent (in) :: b_2
    real(8), intent (in) :: c
    code = (-b_2 + sqrt(((b_2 * b_2) - (a * c)))) / a
end function

↓

real(8) function code(a, b_2, c)
    real(8), intent (in) :: a
    real(8), intent (in) :: b_2
    real(8), intent (in) :: c
    real(8) :: t_0
    real(8) :: tmp
    t_0 = sqrt(((b_2 * b_2) - (a * c)))
    if (b_2 <= (-5d+92)) then
        tmp = ((-2.0d0) * (b_2 / a)) + (0.5d0 * (c / b_2))
    else if (b_2 <= 3.15d-102) then
        tmp = (t_0 - b_2) / a
    else if (b_2 <= 2.4d+46) then
        tmp = ((a * -c) / (b_2 + t_0)) / a
    else
        tmp = (c / b_2) * (-0.5d0)
    end if
    code = tmp
end function

Java

public static double code(double a, double b_2, double c) {
	return (-b_2 + Math.sqrt(((b_2 * b_2) - (a * c)))) / a;
}

↓

public static double code(double a, double b_2, double c) {
	double t_0 = Math.sqrt(((b_2 * b_2) - (a * c)));
	double tmp;
	if (b_2 <= -5e+92) {
		tmp = (-2.0 * (b_2 / a)) + (0.5 * (c / b_2));
	} else if (b_2 <= 3.15e-102) {
		tmp = (t_0 - b_2) / a;
	} else if (b_2 <= 2.4e+46) {
		tmp = ((a * -c) / (b_2 + t_0)) / a;
	} else {
		tmp = (c / b_2) * -0.5;
	}
	return tmp;
}

Python

def code(a, b_2, c):
	return (-b_2 + math.sqrt(((b_2 * b_2) - (a * c)))) / a

↓

def code(a, b_2, c):
	t_0 = math.sqrt(((b_2 * b_2) - (a * c)))
	tmp = 0
	if b_2 <= -5e+92:
		tmp = (-2.0 * (b_2 / a)) + (0.5 * (c / b_2))
	elif b_2 <= 3.15e-102:
		tmp = (t_0 - b_2) / a
	elif b_2 <= 2.4e+46:
		tmp = ((a * -c) / (b_2 + t_0)) / a
	else:
		tmp = (c / b_2) * -0.5
	return tmp

Julia

function code(a, b_2, c)
	return Float64(Float64(Float64(-b_2) + sqrt(Float64(Float64(b_2 * b_2) - Float64(a * c)))) / a)
end

↓

function code(a, b_2, c)
	t_0 = sqrt(Float64(Float64(b_2 * b_2) - Float64(a * c)))
	tmp = 0.0
	if (b_2 <= -5e+92)
		tmp = Float64(Float64(-2.0 * Float64(b_2 / a)) + Float64(0.5 * Float64(c / b_2)));
	elseif (b_2 <= 3.15e-102)
		tmp = Float64(Float64(t_0 - b_2) / a);
	elseif (b_2 <= 2.4e+46)
		tmp = Float64(Float64(Float64(a * Float64(-c)) / Float64(b_2 + t_0)) / a);
	else
		tmp = Float64(Float64(c / b_2) * -0.5);
	end
	return tmp
end

MATLAB

function tmp = code(a, b_2, c)
	tmp = (-b_2 + sqrt(((b_2 * b_2) - (a * c)))) / a;
end

↓

function tmp_2 = code(a, b_2, c)
	t_0 = sqrt(((b_2 * b_2) - (a * c)));
	tmp = 0.0;
	if (b_2 <= -5e+92)
		tmp = (-2.0 * (b_2 / a)) + (0.5 * (c / b_2));
	elseif (b_2 <= 3.15e-102)
		tmp = (t_0 - b_2) / a;
	elseif (b_2 <= 2.4e+46)
		tmp = ((a * -c) / (b_2 + t_0)) / a;
	else
		tmp = (c / b_2) * -0.5;
	end
	tmp_2 = tmp;
end

Wolfram

code[a_, b$95$2_, c_] := N[(N[((-b$95$2) + N[Sqrt[N[(N[(b$95$2 * b$95$2), $MachinePrecision] - N[(a * c), $MachinePrecision]), $MachinePrecision]], $MachinePrecision]), $MachinePrecision] / a), $MachinePrecision]

↓

code[a_, b$95$2_, c_] := Block[{t$95$0 = N[Sqrt[N[(N[(b$95$2 * b$95$2), $MachinePrecision] - N[(a * c), $MachinePrecision]), $MachinePrecision]], $MachinePrecision]}, If[LessEqual[b$95$2, -5e+92], N[(N[(-2.0 * N[(b$95$2 / a), $MachinePrecision]), $MachinePrecision] + N[(0.5 * N[(c / b$95$2), $MachinePrecision]), $MachinePrecision]), $MachinePrecision], If[LessEqual[b$95$2, 3.15e-102], N[(N[(t$95$0 - b$95$2), $MachinePrecision] / a), $MachinePrecision], If[LessEqual[b$95$2, 2.4e+46], N[(N[(N[(a * (-c)), $MachinePrecision] / N[(b$95$2 + t$95$0), $MachinePrecision]), $MachinePrecision] / a), $MachinePrecision], N[(N[(c / b$95$2), $MachinePrecision] * -0.5), $MachinePrecision]]]]]

Derivation

1. Split input into 4 regimes

2. if b_2 < -5.00000000000000022e92

   1. Initial program 26.7%

      \[\frac{\left(-b_2\right) + \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]

   2. Simplified 26.7%

      \[\leadsto \color{blue}{\frac{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}{a}} \]
      Proof

      [Start] 26.7	\[ \frac{\left(-b_2\right) + \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
      +-commutative [=>] 26.7	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - a \cdot c} + \left(-b_2\right)}}{a} \]
      unsub-neg [=>] 26.7	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}}{a} \]

   3. Taylor expanded in b_2 around -inf 94.0%

      \[\leadsto \color{blue}{-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}} \]

   if -5.00000000000000022e92 < b_2 < 3.15e-102

   1. Initial program 81.0%

      \[\frac{\left(-b_2\right) + \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]

   2. Simplified 81.0%

      \[\leadsto \color{blue}{\frac{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}{a}} \]
      Proof

      [Start] 81.0	\[ \frac{\left(-b_2\right) + \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
      +-commutative [=>] 81.0	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - a \cdot c} + \left(-b_2\right)}}{a} \]
      unsub-neg [=>] 81.0	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}}{a} \]

   if 3.15e-102 < b_2 < 2.40000000000000008e46

   1. Initial program 36.8%

      \[\frac{\left(-b_2\right) + \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]

   2. Simplified 36.8%

      \[\leadsto \color{blue}{\frac{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}{a}} \]
      Proof

      [Start] 36.8	\[ \frac{\left(-b_2\right) + \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
      +-commutative [=>] 36.8	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - a \cdot c} + \left(-b_2\right)}}{a} \]
      unsub-neg [=>] 36.8	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}}{a} \]

   3. Applied egg-rr 36.8%

      \[\leadsto \frac{\color{blue}{\frac{\left(b_2 \cdot b_2 - a \cdot c\right) - \left(-b_2\right) \cdot \left(-b_2\right)}{\sqrt{b_2 \cdot b_2 - a \cdot c} - \left(-b_2\right)}}}{a} \]
      Proof

      [Start] 36.8	\[ \frac{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}{a} \]
      sub-neg [=>] 36.8	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - a \cdot c} + \left(-b_2\right)}}{a} \]
      flip-+ [=>] 36.8	\[ \frac{\color{blue}{\frac{\sqrt{b_2 \cdot b_2 - a \cdot c} \cdot \sqrt{b_2 \cdot b_2 - a \cdot c} - \left(-b_2\right) \cdot \left(-b_2\right)}{\sqrt{b_2 \cdot b_2 - a \cdot c} - \left(-b_2\right)}}}{a} \]
      add-sqr-sqrt [<=] 36.8	\[ \frac{\frac{\color{blue}{\left(b_2 \cdot b_2 - a \cdot c\right)} - \left(-b_2\right) \cdot \left(-b_2\right)}{\sqrt{b_2 \cdot b_2 - a \cdot c} - \left(-b_2\right)}}{a} \]

   4. Simplified 36.8%

      \[\leadsto \frac{\color{blue}{\frac{b_2 \cdot b_2 - \left(c \cdot a + b_2 \cdot b_2\right)}{\sqrt{b_2 \cdot b_2 - c \cdot a} - \left(-b_2\right)}}}{a} \]
      Proof

      [Start] 36.8	\[ \frac{\frac{\left(b_2 \cdot b_2 - a \cdot c\right) - \left(-b_2\right) \cdot \left(-b_2\right)}{\sqrt{b_2 \cdot b_2 - a \cdot c} - \left(-b_2\right)}}{a} \]
      associate--l- [=>] 36.8	\[ \frac{\frac{\color{blue}{b_2 \cdot b_2 - \left(a \cdot c + \left(-b_2\right) \cdot \left(-b_2\right)\right)}}{\sqrt{b_2 \cdot b_2 - a \cdot c} - \left(-b_2\right)}}{a} \]
      sqr-neg [=>] 36.8	\[ \frac{\frac{b_2 \cdot b_2 - \left(a \cdot c + \color{blue}{b_2 \cdot b_2}\right)}{\sqrt{b_2 \cdot b_2 - a \cdot c} - \left(-b_2\right)}}{a} \]
      *-commutative [=>] 36.8	\[ \frac{\frac{b_2 \cdot b_2 - \left(\color{blue}{c \cdot a} + b_2 \cdot b_2\right)}{\sqrt{b_2 \cdot b_2 - a \cdot c} - \left(-b_2\right)}}{a} \]
      *-commutative [=>] 36.8	\[ \frac{\frac{b_2 \cdot b_2 - \left(c \cdot a + b_2 \cdot b_2\right)}{\sqrt{b_2 \cdot b_2 - \color{blue}{c \cdot a}} - \left(-b_2\right)}}{a} \]

   5. Applied egg-rr 36.8%

      \[\leadsto \frac{\color{blue}{\left(b_2 \cdot b_2 - \mathsf{fma}\left(b_2, b_2, c \cdot a\right)\right) \cdot \frac{1}{b_2 + \sqrt{b_2 \cdot b_2 - c \cdot a}}}}{a} \]
      Proof

      [Start] 36.8	\[ \frac{\frac{b_2 \cdot b_2 - \left(c \cdot a + b_2 \cdot b_2\right)}{\sqrt{b_2 \cdot b_2 - c \cdot a} - \left(-b_2\right)}}{a} \]
      associate--r+ [=>] 36.8	\[ \frac{\frac{\color{blue}{\left(b_2 \cdot b_2 - c \cdot a\right) - b_2 \cdot b_2}}{\sqrt{b_2 \cdot b_2 - c \cdot a} - \left(-b_2\right)}}{a} \]
      add-sqr-sqrt [=>] 36.8	\[ \frac{\frac{\color{blue}{\sqrt{b_2 \cdot b_2 - c \cdot a} \cdot \sqrt{b_2 \cdot b_2 - c \cdot a}} - b_2 \cdot b_2}{\sqrt{b_2 \cdot b_2 - c \cdot a} - \left(-b_2\right)}}{a} \]
      *-un-lft-identity [=>] 36.8	\[ \frac{\frac{\sqrt{b_2 \cdot b_2 - c \cdot a} \cdot \sqrt{b_2 \cdot b_2 - c \cdot a} - \color{blue}{1 \cdot \left(b_2 \cdot b_2\right)}}{\sqrt{b_2 \cdot b_2 - c \cdot a} - \left(-b_2\right)}}{a} \]
      *-un-lft-identity [<=] 36.8	\[ \frac{\frac{\sqrt{b_2 \cdot b_2 - c \cdot a} \cdot \sqrt{b_2 \cdot b_2 - c \cdot a} - \color{blue}{b_2 \cdot b_2}}{\sqrt{b_2 \cdot b_2 - c \cdot a} - \left(-b_2\right)}}{a} \]
      sqr-neg [<=] 36.8	\[ \frac{\frac{\sqrt{b_2 \cdot b_2 - c \cdot a} \cdot \sqrt{b_2 \cdot b_2 - c \cdot a} - \color{blue}{\left(-b_2\right) \cdot \left(-b_2\right)}}{\sqrt{b_2 \cdot b_2 - c \cdot a} - \left(-b_2\right)}}{a} \]
      flip-+ [<=] 36.8	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - c \cdot a} + \left(-b_2\right)}}{a} \]
      unsub-neg [=>] 36.8	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - c \cdot a} - b_2}}{a} \]
      add-sqr-sqrt [=>] 36.0	\[ \frac{\sqrt{b_2 \cdot b_2 - c \cdot a} - \color{blue}{\sqrt{b_2} \cdot \sqrt{b_2}}}{a} \]
      sqrt-prod [<=] 36.8	\[ \frac{\sqrt{b_2 \cdot b_2 - c \cdot a} - \color{blue}{\sqrt{b_2 \cdot b_2}}}{a} \]
      sqr-neg [<=] 36.8	\[ \frac{\sqrt{b_2 \cdot b_2 - c \cdot a} - \sqrt{\color{blue}{\left(-b_2\right) \cdot \left(-b_2\right)}}}{a} \]
      sqrt-unprod [<=] 0.0	\[ \frac{\sqrt{b_2 \cdot b_2 - c \cdot a} - \color{blue}{\sqrt{-b_2} \cdot \sqrt{-b_2}}}{a} \]
      add-sqr-sqrt [<=] 31.7	\[ \frac{\sqrt{b_2 \cdot b_2 - c \cdot a} - \color{blue}{\left(-b_2\right)}}{a} \]
      flip-- [=>] 29.9	\[ \frac{\color{blue}{\frac{\sqrt{b_2 \cdot b_2 - c \cdot a} \cdot \sqrt{b_2 \cdot b_2 - c \cdot a} - \left(-b_2\right) \cdot \left(-b_2\right)}{\sqrt{b_2 \cdot b_2 - c \cdot a} + \left(-b_2\right)}}}{a} \]
      div-inv [=>] 29.9	\[ \frac{\color{blue}{\left(\sqrt{b_2 \cdot b_2 - c \cdot a} \cdot \sqrt{b_2 \cdot b_2 - c \cdot a} - \left(-b_2\right) \cdot \left(-b_2\right)\right) \cdot \frac{1}{\sqrt{b_2 \cdot b_2 - c \cdot a} + \left(-b_2\right)}}}{a} \]

   6. Simplified 75.0%

      \[\leadsto \frac{\color{blue}{\frac{0 - c \cdot a}{b_2 + \sqrt{b_2 \cdot b_2 - c \cdot a}}}}{a} \]
      Proof

      [Start] 36.8	\[ \frac{\left(b_2 \cdot b_2 - \mathsf{fma}\left(b_2, b_2, c \cdot a\right)\right) \cdot \frac{1}{b_2 + \sqrt{b_2 \cdot b_2 - c \cdot a}}}{a} \]
      associate-*r/ [=>] 36.8	\[ \frac{\color{blue}{\frac{\left(b_2 \cdot b_2 - \mathsf{fma}\left(b_2, b_2, c \cdot a\right)\right) \cdot 1}{b_2 + \sqrt{b_2 \cdot b_2 - c \cdot a}}}}{a} \]
      *-rgt-identity [=>] 36.8	\[ \frac{\frac{\color{blue}{b_2 \cdot b_2 - \mathsf{fma}\left(b_2, b_2, c \cdot a\right)}}{b_2 + \sqrt{b_2 \cdot b_2 - c \cdot a}}}{a} \]
      fma-udef [=>] 36.8	\[ \frac{\frac{b_2 \cdot b_2 - \color{blue}{\left(b_2 \cdot b_2 + c \cdot a\right)}}{b_2 + \sqrt{b_2 \cdot b_2 - c \cdot a}}}{a} \]
      associate--r+ [=>] 75.0	\[ \frac{\frac{\color{blue}{\left(b_2 \cdot b_2 - b_2 \cdot b_2\right) - c \cdot a}}{b_2 + \sqrt{b_2 \cdot b_2 - c \cdot a}}}{a} \]
      +-inverses [=>] 75.0	\[ \frac{\frac{\color{blue}{0} - c \cdot a}{b_2 + \sqrt{b_2 \cdot b_2 - c \cdot a}}}{a} \]

   if 2.40000000000000008e46 < b_2

   1. Initial program 10.3%

      \[\frac{\left(-b_2\right) + \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]

   2. Simplified 10.3%

      \[\leadsto \color{blue}{\frac{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}{a}} \]
      Proof

      [Start] 10.3	\[ \frac{\left(-b_2\right) + \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
      +-commutative [=>] 10.3	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - a \cdot c} + \left(-b_2\right)}}{a} \]
      unsub-neg [=>] 10.3	\[ \frac{\color{blue}{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}}{a} \]

   3. Taylor expanded in b_2 around inf 93.6%

      \[\leadsto \color{blue}{-0.5 \cdot \frac{c}{b_2}} \]
3. Recombined 4 regimes into one program.

4. Final simplification 86.1%

   \[\leadsto \begin{array}{l} \mathbf{if}\;b_2 \leq -5 \cdot 10^{+92}:\\ \;\;\;\;-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}\\ \mathbf{elif}\;b_2 \leq 3.15 \cdot 10^{-102}:\\ \;\;\;\;\frac{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}{a}\\ \mathbf{elif}\;b_2 \leq 2.4 \cdot 10^{+46}:\\ \;\;\;\;\frac{\frac{a \cdot \left(-c\right)}{b_2 + \sqrt{b_2 \cdot b_2 - a \cdot c}}}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{b_2} \cdot -0.5\\ \end{array} \]

Alternatives

Alternative 1
Accuracy	84.3%
Cost	7368

\[\begin{array}{l} \mathbf{if}\;b_2 \leq -7 \cdot 10^{+92}:\\ \;\;\;\;-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}\\ \mathbf{elif}\;b_2 \leq 4.2 \cdot 10^{-36}:\\ \;\;\;\;\frac{\sqrt{b_2 \cdot b_2 - a \cdot c} - b_2}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{b_2} \cdot -0.5\\ \end{array} \]

Alternative 2
Accuracy	77.3%
Cost	7176

\[\begin{array}{l} \mathbf{if}\;b_2 \leq -1.15 \cdot 10^{+25}:\\ \;\;\;\;-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}\\ \mathbf{elif}\;b_2 \leq 7 \cdot 10^{-36}:\\ \;\;\;\;\frac{\sqrt{a \cdot \left(-c\right)} - b_2}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{b_2} \cdot -0.5\\ \end{array} \]

Alternative 3
Accuracy	78.4%
Cost	7048

\[\begin{array}{l} \mathbf{if}\;b_2 \leq -6.8 \cdot 10^{-52}:\\ \;\;\;\;-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}\\ \mathbf{elif}\;b_2 \leq 1.5 \cdot 10^{-35}:\\ \;\;\;\;\frac{\sqrt{a \cdot \left(-c\right)}}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{b_2} \cdot -0.5\\ \end{array} \]

Alternative 4
Accuracy	64.6%
Cost	452

\[\begin{array}{l} \mathbf{if}\;b_2 \leq 4.8 \cdot 10^{-304}:\\ \;\;\;\;\frac{-2}{\frac{a}{b_2}}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{b_2} \cdot -0.5\\ \end{array} \]

Alternative 5
Accuracy	64.7%
Cost	452

\[\begin{array}{l} \mathbf{if}\;b_2 \leq 4.8 \cdot 10^{-304}:\\ \;\;\;\;\frac{b_2 \cdot -2}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{b_2} \cdot -0.5\\ \end{array} \]

Alternative 6
Accuracy	38.1%
Cost	320

\[\frac{c}{b_2} \cdot -0.5 \]

Reproduce

herbie shell --seed 2023133 
(FPCore (a b_2 c)
  :name "quad2p (problem 3.2.1, positive)"
  :precision binary64
  (/ (+ (- b_2) (sqrt (- (* b_2 b_2) (* a c)))) a))