quad2m (problem 3.2.1, negative)

Percentage Accurate: 52.0% → 84.5%
Time: 9.2s
Alternatives: 5
Speedup: 15.9×

Specification

?
\[\begin{array}{l} \\ \frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \end{array} \]
(FPCore (a b_2 c)
 :precision binary64
 (/ (- (- b_2) (sqrt (- (* b_2 b_2) (* a c)))) a))
double code(double a, double b_2, double c) {
	return (-b_2 - sqrt(((b_2 * b_2) - (a * c)))) / a;
}
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
public static double code(double a, double b_2, double c) {
	return (-b_2 - Math.sqrt(((b_2 * b_2) - (a * c)))) / a;
}
def code(a, b_2, c):
	return (-b_2 - math.sqrt(((b_2 * b_2) - (a * c)))) / a
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 tmp = code(a, b_2, c)
	tmp = (-b_2 - sqrt(((b_2 * b_2) - (a * c)))) / a;
end
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]
\begin{array}{l}

\\
\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a}
\end{array}

Sampling outcomes in binary64 precision:

Local Percentage Accuracy vs ?

The average percentage accuracy by input value. Horizontal axis shows value of an input variable; the variable is choosen in the title. Vertical axis is accuracy; higher is better. Red represent the original program, while blue represents Herbie's suggestion. These can be toggled with buttons below the plot. The line is an average while dots represent individual samples.

Accuracy vs Speed?

Herbie found 5 alternatives:

AlternativeAccuracySpeedup
The accuracy (vertical axis) and speed (horizontal axis) of each alternatives. Up and to the right is better. The red square shows the initial program, and each blue circle shows an alternative.The line shows the best available speed-accuracy tradeoffs.

Initial Program: 52.0% accurate, 1.0× speedup?

\[\begin{array}{l} \\ \frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \end{array} \]
(FPCore (a b_2 c)
 :precision binary64
 (/ (- (- b_2) (sqrt (- (* b_2 b_2) (* a c)))) a))
double code(double a, double b_2, double c) {
	return (-b_2 - sqrt(((b_2 * b_2) - (a * c)))) / a;
}
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
public static double code(double a, double b_2, double c) {
	return (-b_2 - Math.sqrt(((b_2 * b_2) - (a * c)))) / a;
}
def code(a, b_2, c):
	return (-b_2 - math.sqrt(((b_2 * b_2) - (a * c)))) / a
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 tmp = code(a, b_2, c)
	tmp = (-b_2 - sqrt(((b_2 * b_2) - (a * c)))) / a;
end
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]
\begin{array}{l}

\\
\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a}
\end{array}

Alternative 1: 84.5% accurate, 1.0× speedup?

\[\begin{array}{l} \\ \begin{array}{l} \mathbf{if}\;b_2 \leq -2.05 \cdot 10^{-27}:\\ \;\;\;\;\frac{-0.5 \cdot c}{b_2}\\ \mathbf{elif}\;b_2 \leq 8 \cdot 10^{+105}:\\ \;\;\;\;\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - c \cdot a}}{a}\\ \mathbf{else}:\\ \;\;\;\;-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}\\ \end{array} \end{array} \]
(FPCore (a b_2 c)
 :precision binary64
 (if (<= b_2 -2.05e-27)
   (/ (* -0.5 c) b_2)
   (if (<= b_2 8e+105)
     (/ (- (- b_2) (sqrt (- (* b_2 b_2) (* c a)))) a)
     (+ (* -2.0 (/ b_2 a)) (* 0.5 (/ c b_2))))))
double code(double a, double b_2, double c) {
	double tmp;
	if (b_2 <= -2.05e-27) {
		tmp = (-0.5 * c) / b_2;
	} else if (b_2 <= 8e+105) {
		tmp = (-b_2 - sqrt(((b_2 * b_2) - (c * a)))) / a;
	} else {
		tmp = (-2.0 * (b_2 / a)) + (0.5 * (c / b_2));
	}
	return tmp;
}
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) :: tmp
    if (b_2 <= (-2.05d-27)) then
        tmp = ((-0.5d0) * c) / b_2
    else if (b_2 <= 8d+105) then
        tmp = (-b_2 - sqrt(((b_2 * b_2) - (c * a)))) / a
    else
        tmp = ((-2.0d0) * (b_2 / a)) + (0.5d0 * (c / b_2))
    end if
    code = tmp
end function
public static double code(double a, double b_2, double c) {
	double tmp;
	if (b_2 <= -2.05e-27) {
		tmp = (-0.5 * c) / b_2;
	} else if (b_2 <= 8e+105) {
		tmp = (-b_2 - Math.sqrt(((b_2 * b_2) - (c * a)))) / a;
	} else {
		tmp = (-2.0 * (b_2 / a)) + (0.5 * (c / b_2));
	}
	return tmp;
}
def code(a, b_2, c):
	tmp = 0
	if b_2 <= -2.05e-27:
		tmp = (-0.5 * c) / b_2
	elif b_2 <= 8e+105:
		tmp = (-b_2 - math.sqrt(((b_2 * b_2) - (c * a)))) / a
	else:
		tmp = (-2.0 * (b_2 / a)) + (0.5 * (c / b_2))
	return tmp
function code(a, b_2, c)
	tmp = 0.0
	if (b_2 <= -2.05e-27)
		tmp = Float64(Float64(-0.5 * c) / b_2);
	elseif (b_2 <= 8e+105)
		tmp = Float64(Float64(Float64(-b_2) - sqrt(Float64(Float64(b_2 * b_2) - Float64(c * a)))) / a);
	else
		tmp = Float64(Float64(-2.0 * Float64(b_2 / a)) + Float64(0.5 * Float64(c / b_2)));
	end
	return tmp
end
function tmp_2 = code(a, b_2, c)
	tmp = 0.0;
	if (b_2 <= -2.05e-27)
		tmp = (-0.5 * c) / b_2;
	elseif (b_2 <= 8e+105)
		tmp = (-b_2 - sqrt(((b_2 * b_2) - (c * a)))) / a;
	else
		tmp = (-2.0 * (b_2 / a)) + (0.5 * (c / b_2));
	end
	tmp_2 = tmp;
end
code[a_, b$95$2_, c_] := If[LessEqual[b$95$2, -2.05e-27], N[(N[(-0.5 * c), $MachinePrecision] / b$95$2), $MachinePrecision], If[LessEqual[b$95$2, 8e+105], N[(N[((-b$95$2) - N[Sqrt[N[(N[(b$95$2 * b$95$2), $MachinePrecision] - N[(c * a), $MachinePrecision]), $MachinePrecision]], $MachinePrecision]), $MachinePrecision] / a), $MachinePrecision], N[(N[(-2.0 * N[(b$95$2 / a), $MachinePrecision]), $MachinePrecision] + N[(0.5 * N[(c / b$95$2), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]]]
\begin{array}{l}

\\
\begin{array}{l}
\mathbf{if}\;b_2 \leq -2.05 \cdot 10^{-27}:\\
\;\;\;\;\frac{-0.5 \cdot c}{b_2}\\

\mathbf{elif}\;b_2 \leq 8 \cdot 10^{+105}:\\
\;\;\;\;\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - c \cdot a}}{a}\\

\mathbf{else}:\\
\;\;\;\;-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}\\


\end{array}
\end{array}
Derivation
  1. Split input into 3 regimes
  2. if b_2 < -2.0499999999999999e-27

    1. Initial program 13.0%

      \[\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
    2. Taylor expanded in b_2 around -inf 93.1%

      \[\leadsto \color{blue}{-0.5 \cdot \frac{c}{b_2}} \]
    3. Step-by-step derivation
      1. associate-*r/93.2%

        \[\leadsto \color{blue}{\frac{-0.5 \cdot c}{b_2}} \]
    4. Applied egg-rr93.2%

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

    if -2.0499999999999999e-27 < b_2 < 7.9999999999999995e105

    1. Initial program 81.4%

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

    if 7.9999999999999995e105 < b_2

    1. Initial program 61.1%

      \[\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
    2. Taylor expanded in b_2 around inf 97.2%

      \[\leadsto \color{blue}{-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}} \]
  3. Recombined 3 regimes into one program.
  4. Final simplification89.3%

    \[\leadsto \begin{array}{l} \mathbf{if}\;b_2 \leq -2.05 \cdot 10^{-27}:\\ \;\;\;\;\frac{-0.5 \cdot c}{b_2}\\ \mathbf{elif}\;b_2 \leq 8 \cdot 10^{+105}:\\ \;\;\;\;\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - c \cdot a}}{a}\\ \mathbf{else}:\\ \;\;\;\;-2 \cdot \frac{b_2}{a} + 0.5 \cdot \frac{c}{b_2}\\ \end{array} \]

Alternative 2: 79.3% accurate, 1.0× speedup?

\[\begin{array}{l} \\ \begin{array}{l} \mathbf{if}\;b_2 \leq -2.05 \cdot 10^{-27}:\\ \;\;\;\;\frac{-0.5 \cdot c}{b_2}\\ \mathbf{elif}\;b_2 \leq 2.3 \cdot 10^{-26}:\\ \;\;\;\;\frac{\left(-b_2\right) - \sqrt{c \cdot \left(-a\right)}}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{b_2 \cdot -2}{a}\\ \end{array} \end{array} \]
(FPCore (a b_2 c)
 :precision binary64
 (if (<= b_2 -2.05e-27)
   (/ (* -0.5 c) b_2)
   (if (<= b_2 2.3e-26)
     (/ (- (- b_2) (sqrt (* c (- a)))) a)
     (/ (* b_2 -2.0) a))))
double code(double a, double b_2, double c) {
	double tmp;
	if (b_2 <= -2.05e-27) {
		tmp = (-0.5 * c) / b_2;
	} else if (b_2 <= 2.3e-26) {
		tmp = (-b_2 - sqrt((c * -a))) / a;
	} else {
		tmp = (b_2 * -2.0) / a;
	}
	return tmp;
}
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) :: tmp
    if (b_2 <= (-2.05d-27)) then
        tmp = ((-0.5d0) * c) / b_2
    else if (b_2 <= 2.3d-26) then
        tmp = (-b_2 - sqrt((c * -a))) / a
    else
        tmp = (b_2 * (-2.0d0)) / a
    end if
    code = tmp
end function
public static double code(double a, double b_2, double c) {
	double tmp;
	if (b_2 <= -2.05e-27) {
		tmp = (-0.5 * c) / b_2;
	} else if (b_2 <= 2.3e-26) {
		tmp = (-b_2 - Math.sqrt((c * -a))) / a;
	} else {
		tmp = (b_2 * -2.0) / a;
	}
	return tmp;
}
def code(a, b_2, c):
	tmp = 0
	if b_2 <= -2.05e-27:
		tmp = (-0.5 * c) / b_2
	elif b_2 <= 2.3e-26:
		tmp = (-b_2 - math.sqrt((c * -a))) / a
	else:
		tmp = (b_2 * -2.0) / a
	return tmp
function code(a, b_2, c)
	tmp = 0.0
	if (b_2 <= -2.05e-27)
		tmp = Float64(Float64(-0.5 * c) / b_2);
	elseif (b_2 <= 2.3e-26)
		tmp = Float64(Float64(Float64(-b_2) - sqrt(Float64(c * Float64(-a)))) / a);
	else
		tmp = Float64(Float64(b_2 * -2.0) / a);
	end
	return tmp
end
function tmp_2 = code(a, b_2, c)
	tmp = 0.0;
	if (b_2 <= -2.05e-27)
		tmp = (-0.5 * c) / b_2;
	elseif (b_2 <= 2.3e-26)
		tmp = (-b_2 - sqrt((c * -a))) / a;
	else
		tmp = (b_2 * -2.0) / a;
	end
	tmp_2 = tmp;
end
code[a_, b$95$2_, c_] := If[LessEqual[b$95$2, -2.05e-27], N[(N[(-0.5 * c), $MachinePrecision] / b$95$2), $MachinePrecision], If[LessEqual[b$95$2, 2.3e-26], N[(N[((-b$95$2) - N[Sqrt[N[(c * (-a)), $MachinePrecision]], $MachinePrecision]), $MachinePrecision] / a), $MachinePrecision], N[(N[(b$95$2 * -2.0), $MachinePrecision] / a), $MachinePrecision]]]
\begin{array}{l}

\\
\begin{array}{l}
\mathbf{if}\;b_2 \leq -2.05 \cdot 10^{-27}:\\
\;\;\;\;\frac{-0.5 \cdot c}{b_2}\\

\mathbf{elif}\;b_2 \leq 2.3 \cdot 10^{-26}:\\
\;\;\;\;\frac{\left(-b_2\right) - \sqrt{c \cdot \left(-a\right)}}{a}\\

\mathbf{else}:\\
\;\;\;\;\frac{b_2 \cdot -2}{a}\\


\end{array}
\end{array}
Derivation
  1. Split input into 3 regimes
  2. if b_2 < -2.0499999999999999e-27

    1. Initial program 13.0%

      \[\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
    2. Taylor expanded in b_2 around -inf 93.1%

      \[\leadsto \color{blue}{-0.5 \cdot \frac{c}{b_2}} \]
    3. Step-by-step derivation
      1. associate-*r/93.2%

        \[\leadsto \color{blue}{\frac{-0.5 \cdot c}{b_2}} \]
    4. Applied egg-rr93.2%

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

    if -2.0499999999999999e-27 < b_2 < 2.30000000000000009e-26

    1. Initial program 76.5%

      \[\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
    2. Taylor expanded in b_2 around 0 70.0%

      \[\leadsto \frac{\left(-b_2\right) - \sqrt{\color{blue}{-1 \cdot \left(a \cdot c\right)}}}{a} \]
    3. Step-by-step derivation
      1. associate-*r*70.0%

        \[\leadsto \frac{\left(-b_2\right) - \sqrt{\color{blue}{\left(-1 \cdot a\right) \cdot c}}}{a} \]
      2. neg-mul-170.0%

        \[\leadsto \frac{\left(-b_2\right) - \sqrt{\color{blue}{\left(-a\right)} \cdot c}}{a} \]
    4. Simplified70.0%

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

    if 2.30000000000000009e-26 < b_2

    1. Initial program 71.3%

      \[\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
    2. Taylor expanded in b_2 around inf 92.1%

      \[\leadsto \frac{\color{blue}{-2 \cdot b_2}}{a} \]
    3. Step-by-step derivation
      1. *-commutative92.1%

        \[\leadsto \frac{\color{blue}{b_2 \cdot -2}}{a} \]
    4. Simplified92.1%

      \[\leadsto \frac{\color{blue}{b_2 \cdot -2}}{a} \]
  3. Recombined 3 regimes into one program.
  4. Final simplification85.4%

    \[\leadsto \begin{array}{l} \mathbf{if}\;b_2 \leq -2.05 \cdot 10^{-27}:\\ \;\;\;\;\frac{-0.5 \cdot c}{b_2}\\ \mathbf{elif}\;b_2 \leq 2.3 \cdot 10^{-26}:\\ \;\;\;\;\frac{\left(-b_2\right) - \sqrt{c \cdot \left(-a\right)}}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{b_2 \cdot -2}{a}\\ \end{array} \]

Alternative 3: 67.3% accurate, 15.9× speedup?

\[\begin{array}{l} \\ \begin{array}{l} \mathbf{if}\;b_2 \leq -5.6 \cdot 10^{-308}:\\ \;\;\;\;\frac{-0.5 \cdot c}{b_2}\\ \mathbf{else}:\\ \;\;\;\;\frac{b_2 \cdot -2}{a}\\ \end{array} \end{array} \]
(FPCore (a b_2 c)
 :precision binary64
 (if (<= b_2 -5.6e-308) (/ (* -0.5 c) b_2) (/ (* b_2 -2.0) a)))
double code(double a, double b_2, double c) {
	double tmp;
	if (b_2 <= -5.6e-308) {
		tmp = (-0.5 * c) / b_2;
	} else {
		tmp = (b_2 * -2.0) / a;
	}
	return tmp;
}
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) :: tmp
    if (b_2 <= (-5.6d-308)) then
        tmp = ((-0.5d0) * c) / b_2
    else
        tmp = (b_2 * (-2.0d0)) / a
    end if
    code = tmp
end function
public static double code(double a, double b_2, double c) {
	double tmp;
	if (b_2 <= -5.6e-308) {
		tmp = (-0.5 * c) / b_2;
	} else {
		tmp = (b_2 * -2.0) / a;
	}
	return tmp;
}
def code(a, b_2, c):
	tmp = 0
	if b_2 <= -5.6e-308:
		tmp = (-0.5 * c) / b_2
	else:
		tmp = (b_2 * -2.0) / a
	return tmp
function code(a, b_2, c)
	tmp = 0.0
	if (b_2 <= -5.6e-308)
		tmp = Float64(Float64(-0.5 * c) / b_2);
	else
		tmp = Float64(Float64(b_2 * -2.0) / a);
	end
	return tmp
end
function tmp_2 = code(a, b_2, c)
	tmp = 0.0;
	if (b_2 <= -5.6e-308)
		tmp = (-0.5 * c) / b_2;
	else
		tmp = (b_2 * -2.0) / a;
	end
	tmp_2 = tmp;
end
code[a_, b$95$2_, c_] := If[LessEqual[b$95$2, -5.6e-308], N[(N[(-0.5 * c), $MachinePrecision] / b$95$2), $MachinePrecision], N[(N[(b$95$2 * -2.0), $MachinePrecision] / a), $MachinePrecision]]
\begin{array}{l}

\\
\begin{array}{l}
\mathbf{if}\;b_2 \leq -5.6 \cdot 10^{-308}:\\
\;\;\;\;\frac{-0.5 \cdot c}{b_2}\\

\mathbf{else}:\\
\;\;\;\;\frac{b_2 \cdot -2}{a}\\


\end{array}
\end{array}
Derivation
  1. Split input into 2 regimes
  2. if b_2 < -5.59999999999999969e-308

    1. Initial program 33.2%

      \[\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
    2. Taylor expanded in b_2 around -inf 65.4%

      \[\leadsto \color{blue}{-0.5 \cdot \frac{c}{b_2}} \]
    3. Step-by-step derivation
      1. associate-*r/65.4%

        \[\leadsto \color{blue}{\frac{-0.5 \cdot c}{b_2}} \]
    4. Applied egg-rr65.4%

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

    if -5.59999999999999969e-308 < b_2

    1. Initial program 74.6%

      \[\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
    2. Taylor expanded in b_2 around inf 73.3%

      \[\leadsto \frac{\color{blue}{-2 \cdot b_2}}{a} \]
    3. Step-by-step derivation
      1. *-commutative73.3%

        \[\leadsto \frac{\color{blue}{b_2 \cdot -2}}{a} \]
    4. Simplified73.3%

      \[\leadsto \frac{\color{blue}{b_2 \cdot -2}}{a} \]
  3. Recombined 2 regimes into one program.
  4. Final simplification69.4%

    \[\leadsto \begin{array}{l} \mathbf{if}\;b_2 \leq -5.6 \cdot 10^{-308}:\\ \;\;\;\;\frac{-0.5 \cdot c}{b_2}\\ \mathbf{else}:\\ \;\;\;\;\frac{b_2 \cdot -2}{a}\\ \end{array} \]

Alternative 4: 35.3% accurate, 22.4× speedup?

\[\begin{array}{l} \\ -0.5 \cdot \frac{c}{b_2} \end{array} \]
(FPCore (a b_2 c) :precision binary64 (* -0.5 (/ c b_2)))
double code(double a, double b_2, double c) {
	return -0.5 * (c / b_2);
}
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 = (-0.5d0) * (c / b_2)
end function
public static double code(double a, double b_2, double c) {
	return -0.5 * (c / b_2);
}
def code(a, b_2, c):
	return -0.5 * (c / b_2)
function code(a, b_2, c)
	return Float64(-0.5 * Float64(c / b_2))
end
function tmp = code(a, b_2, c)
	tmp = -0.5 * (c / b_2);
end
code[a_, b$95$2_, c_] := N[(-0.5 * N[(c / b$95$2), $MachinePrecision]), $MachinePrecision]
\begin{array}{l}

\\
-0.5 \cdot \frac{c}{b_2}
\end{array}
Derivation
  1. Initial program 54.3%

    \[\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
  2. Taylor expanded in b_2 around -inf 33.3%

    \[\leadsto \color{blue}{-0.5 \cdot \frac{c}{b_2}} \]
  3. Final simplification33.3%

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

Alternative 5: 35.3% accurate, 22.4× speedup?

\[\begin{array}{l} \\ \frac{-0.5 \cdot c}{b_2} \end{array} \]
(FPCore (a b_2 c) :precision binary64 (/ (* -0.5 c) b_2))
double code(double a, double b_2, double c) {
	return (-0.5 * c) / b_2;
}
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 = ((-0.5d0) * c) / b_2
end function
public static double code(double a, double b_2, double c) {
	return (-0.5 * c) / b_2;
}
def code(a, b_2, c):
	return (-0.5 * c) / b_2
function code(a, b_2, c)
	return Float64(Float64(-0.5 * c) / b_2)
end
function tmp = code(a, b_2, c)
	tmp = (-0.5 * c) / b_2;
end
code[a_, b$95$2_, c_] := N[(N[(-0.5 * c), $MachinePrecision] / b$95$2), $MachinePrecision]
\begin{array}{l}

\\
\frac{-0.5 \cdot c}{b_2}
\end{array}
Derivation
  1. Initial program 54.3%

    \[\frac{\left(-b_2\right) - \sqrt{b_2 \cdot b_2 - a \cdot c}}{a} \]
  2. Taylor expanded in b_2 around -inf 33.3%

    \[\leadsto \color{blue}{-0.5 \cdot \frac{c}{b_2}} \]
  3. Step-by-step derivation
    1. associate-*r/33.4%

      \[\leadsto \color{blue}{\frac{-0.5 \cdot c}{b_2}} \]
  4. Applied egg-rr33.4%

    \[\leadsto \color{blue}{\frac{-0.5 \cdot c}{b_2}} \]
  5. Final simplification33.4%

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

Developer target: 99.7% accurate, 0.1× speedup?

\[\begin{array}{l} \\ \begin{array}{l} t_0 := \sqrt{\left|a\right|} \cdot \sqrt{\left|c\right|}\\ t_1 := \begin{array}{l} \mathbf{if}\;\mathsf{copysign}\left(a, c\right) = a:\\ \;\;\;\;\sqrt{\left|b_2\right| - t_0} \cdot \sqrt{\left|b_2\right| + t_0}\\ \mathbf{else}:\\ \;\;\;\;\mathsf{hypot}\left(b_2, t_0\right)\\ \end{array}\\ \mathbf{if}\;b_2 < 0:\\ \;\;\;\;\frac{c}{t_1 - b_2}\\ \mathbf{else}:\\ \;\;\;\;\frac{b_2 + t_1}{-a}\\ \end{array} \end{array} \]
(FPCore (a b_2 c)
 :precision binary64
 (let* ((t_0 (* (sqrt (fabs a)) (sqrt (fabs c))))
        (t_1
         (if (== (copysign a c) a)
           (* (sqrt (- (fabs b_2) t_0)) (sqrt (+ (fabs b_2) t_0)))
           (hypot b_2 t_0))))
   (if (< b_2 0.0) (/ c (- t_1 b_2)) (/ (+ b_2 t_1) (- a)))))
double code(double a, double b_2, double c) {
	double t_0 = sqrt(fabs(a)) * sqrt(fabs(c));
	double tmp;
	if (copysign(a, c) == a) {
		tmp = sqrt((fabs(b_2) - t_0)) * sqrt((fabs(b_2) + t_0));
	} else {
		tmp = hypot(b_2, t_0);
	}
	double t_1 = tmp;
	double tmp_1;
	if (b_2 < 0.0) {
		tmp_1 = c / (t_1 - b_2);
	} else {
		tmp_1 = (b_2 + t_1) / -a;
	}
	return tmp_1;
}
public static double code(double a, double b_2, double c) {
	double t_0 = Math.sqrt(Math.abs(a)) * Math.sqrt(Math.abs(c));
	double tmp;
	if (Math.copySign(a, c) == a) {
		tmp = Math.sqrt((Math.abs(b_2) - t_0)) * Math.sqrt((Math.abs(b_2) + t_0));
	} else {
		tmp = Math.hypot(b_2, t_0);
	}
	double t_1 = tmp;
	double tmp_1;
	if (b_2 < 0.0) {
		tmp_1 = c / (t_1 - b_2);
	} else {
		tmp_1 = (b_2 + t_1) / -a;
	}
	return tmp_1;
}
def code(a, b_2, c):
	t_0 = math.sqrt(math.fabs(a)) * math.sqrt(math.fabs(c))
	tmp = 0
	if math.copysign(a, c) == a:
		tmp = math.sqrt((math.fabs(b_2) - t_0)) * math.sqrt((math.fabs(b_2) + t_0))
	else:
		tmp = math.hypot(b_2, t_0)
	t_1 = tmp
	tmp_1 = 0
	if b_2 < 0.0:
		tmp_1 = c / (t_1 - b_2)
	else:
		tmp_1 = (b_2 + t_1) / -a
	return tmp_1
function code(a, b_2, c)
	t_0 = Float64(sqrt(abs(a)) * sqrt(abs(c)))
	tmp = 0.0
	if (copysign(a, c) == a)
		tmp = Float64(sqrt(Float64(abs(b_2) - t_0)) * sqrt(Float64(abs(b_2) + t_0)));
	else
		tmp = hypot(b_2, t_0);
	end
	t_1 = tmp
	tmp_1 = 0.0
	if (b_2 < 0.0)
		tmp_1 = Float64(c / Float64(t_1 - b_2));
	else
		tmp_1 = Float64(Float64(b_2 + t_1) / Float64(-a));
	end
	return tmp_1
end
function tmp_3 = code(a, b_2, c)
	t_0 = sqrt(abs(a)) * sqrt(abs(c));
	tmp = 0.0;
	if ((sign(c) * abs(a)) == a)
		tmp = sqrt((abs(b_2) - t_0)) * sqrt((abs(b_2) + t_0));
	else
		tmp = hypot(b_2, t_0);
	end
	t_1 = tmp;
	tmp_2 = 0.0;
	if (b_2 < 0.0)
		tmp_2 = c / (t_1 - b_2);
	else
		tmp_2 = (b_2 + t_1) / -a;
	end
	tmp_3 = tmp_2;
end
code[a_, b$95$2_, c_] := Block[{t$95$0 = N[(N[Sqrt[N[Abs[a], $MachinePrecision]], $MachinePrecision] * N[Sqrt[N[Abs[c], $MachinePrecision]], $MachinePrecision]), $MachinePrecision]}, Block[{t$95$1 = If[Equal[N[With[{TMP1 = Abs[a], TMP2 = Sign[c]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision], a], N[(N[Sqrt[N[(N[Abs[b$95$2], $MachinePrecision] - t$95$0), $MachinePrecision]], $MachinePrecision] * N[Sqrt[N[(N[Abs[b$95$2], $MachinePrecision] + t$95$0), $MachinePrecision]], $MachinePrecision]), $MachinePrecision], N[Sqrt[b$95$2 ^ 2 + t$95$0 ^ 2], $MachinePrecision]]}, If[Less[b$95$2, 0.0], N[(c / N[(t$95$1 - b$95$2), $MachinePrecision]), $MachinePrecision], N[(N[(b$95$2 + t$95$1), $MachinePrecision] / (-a)), $MachinePrecision]]]]
\begin{array}{l}

\\
\begin{array}{l}
t_0 := \sqrt{\left|a\right|} \cdot \sqrt{\left|c\right|}\\
t_1 := \begin{array}{l}
\mathbf{if}\;\mathsf{copysign}\left(a, c\right) = a:\\
\;\;\;\;\sqrt{\left|b_2\right| - t_0} \cdot \sqrt{\left|b_2\right| + t_0}\\

\mathbf{else}:\\
\;\;\;\;\mathsf{hypot}\left(b_2, t_0\right)\\


\end{array}\\
\mathbf{if}\;b_2 < 0:\\
\;\;\;\;\frac{c}{t_1 - b_2}\\

\mathbf{else}:\\
\;\;\;\;\frac{b_2 + t_1}{-a}\\


\end{array}
\end{array}

Reproduce

?
herbie shell --seed 2023320 
(FPCore (a b_2 c)
  :name "quad2m (problem 3.2.1, negative)"
  :precision binary64
  :herbie-expected 10

  :herbie-target
  (if (< b_2 0.0) (/ c (- (if (== (copysign a c) a) (* (sqrt (- (fabs b_2) (* (sqrt (fabs a)) (sqrt (fabs c))))) (sqrt (+ (fabs b_2) (* (sqrt (fabs a)) (sqrt (fabs c)))))) (hypot b_2 (* (sqrt (fabs a)) (sqrt (fabs c))))) b_2)) (/ (+ b_2 (if (== (copysign a c) a) (* (sqrt (- (fabs b_2) (* (sqrt (fabs a)) (sqrt (fabs c))))) (sqrt (+ (fabs b_2) (* (sqrt (fabs a)) (sqrt (fabs c)))))) (hypot b_2 (* (sqrt (fabs a)) (sqrt (fabs c)))))) (- a)))

  (/ (- (- b_2) (sqrt (- (* b_2 b_2) (* a c)))) a))