sqrt B (should all be same)

Average Error: 48.19% → 0.68%

Time: 4.5s

Precision: binary64

Cost: 13380

Math

\[\sqrt{\left(2 \cdot x\right) \cdot x} \]

↓

\[\begin{array}{l} \mathbf{if}\;x \leq -5 \cdot 10^{-310}:\\ \;\;\;\;x \cdot \left(-\sqrt{2}\right)\\ \mathbf{else}:\\ \;\;\;\;{2}^{0.25} \cdot \left({2}^{0.25} \cdot x\right)\\ \end{array} \]

FPCore

(FPCore (x) :precision binary64 (sqrt (* (* 2.0 x) x)))

↓

(FPCore (x)
 :precision binary64
 (if (<= x -5e-310)
   (* x (- (sqrt 2.0)))
   (* (pow 2.0 0.25) (* (pow 2.0 0.25) x))))

C

double code(double x) {
	return sqrt(((2.0 * x) * x));
}

↓

double code(double x) {
	double tmp;
	if (x <= -5e-310) {
		tmp = x * -sqrt(2.0);
	} else {
		tmp = pow(2.0, 0.25) * (pow(2.0, 0.25) * x);
	}
	return tmp;
}

Fortran

real(8) function code(x)
    real(8), intent (in) :: x
    code = sqrt(((2.0d0 * x) * x))
end function

↓

real(8) function code(x)
    real(8), intent (in) :: x
    real(8) :: tmp
    if (x <= (-5d-310)) then
        tmp = x * -sqrt(2.0d0)
    else
        tmp = (2.0d0 ** 0.25d0) * ((2.0d0 ** 0.25d0) * x)
    end if
    code = tmp
end function

Java

public static double code(double x) {
	return Math.sqrt(((2.0 * x) * x));
}

↓

public static double code(double x) {
	double tmp;
	if (x <= -5e-310) {
		tmp = x * -Math.sqrt(2.0);
	} else {
		tmp = Math.pow(2.0, 0.25) * (Math.pow(2.0, 0.25) * x);
	}
	return tmp;
}

Python

def code(x):
	return math.sqrt(((2.0 * x) * x))

↓

def code(x):
	tmp = 0
	if x <= -5e-310:
		tmp = x * -math.sqrt(2.0)
	else:
		tmp = math.pow(2.0, 0.25) * (math.pow(2.0, 0.25) * x)
	return tmp

Julia

function code(x)
	return sqrt(Float64(Float64(2.0 * x) * x))
end

↓

function code(x)
	tmp = 0.0
	if (x <= -5e-310)
		tmp = Float64(x * Float64(-sqrt(2.0)));
	else
		tmp = Float64((2.0 ^ 0.25) * Float64((2.0 ^ 0.25) * x));
	end
	return tmp
end

MATLAB

function tmp = code(x)
	tmp = sqrt(((2.0 * x) * x));
end

↓

function tmp_2 = code(x)
	tmp = 0.0;
	if (x <= -5e-310)
		tmp = x * -sqrt(2.0);
	else
		tmp = (2.0 ^ 0.25) * ((2.0 ^ 0.25) * x);
	end
	tmp_2 = tmp;
end

Wolfram

code[x_] := N[Sqrt[N[(N[(2.0 * x), $MachinePrecision] * x), $MachinePrecision]], $MachinePrecision]

↓

code[x_] := If[LessEqual[x, -5e-310], N[(x * (-N[Sqrt[2.0], $MachinePrecision])), $MachinePrecision], N[(N[Power[2.0, 0.25], $MachinePrecision] * N[(N[Power[2.0, 0.25], $MachinePrecision] * x), $MachinePrecision]), $MachinePrecision]]

Derivation

1. Split input into 2 regimes

2. if x < -4.999999999999985e-310

   1. Initial program 47.65

      \[\sqrt{\left(2 \cdot x\right) \cdot x} \]

   2. Taylor expanded in x around -inf 0.68

      \[\leadsto \color{blue}{-1 \cdot \left(\sqrt{2} \cdot x\right)} \]

   3. Simplified 0.68

      \[\leadsto \color{blue}{\sqrt{2} \cdot \left(-x\right)} \]
      Proof

      [Start] 0.68	\[ -1 \cdot \left(\sqrt{2} \cdot x\right) \]
      mul-1-neg [=>] 0.68	\[ \color{blue}{-\sqrt{2} \cdot x} \]
      distribute-rgt-neg-in [=>] 0.68	\[ \color{blue}{\sqrt{2} \cdot \left(-x\right)} \]

   if -4.999999999999985e-310 < x

   1. Initial program 48.74

      \[\sqrt{\left(2 \cdot x\right) \cdot x} \]

   2. Applied egg-rr 1.05

      \[\leadsto \color{blue}{{\left(\sqrt{\sqrt{2} \cdot x}\right)}^{2}} \]

   3. Applied egg-rr 0.68

      \[\leadsto \color{blue}{{2}^{0.25} \cdot \left({2}^{0.25} \cdot x\right)} \]
3. Recombined 2 regimes into one program.

4. Final simplification 0.68

   \[\leadsto \begin{array}{l} \mathbf{if}\;x \leq -5 \cdot 10^{-310}:\\ \;\;\;\;x \cdot \left(-\sqrt{2}\right)\\ \mathbf{else}:\\ \;\;\;\;{2}^{0.25} \cdot \left({2}^{0.25} \cdot x\right)\\ \end{array} \]

Alternatives

Alternative 1
Error	0.68%
Cost	19648

\[{2}^{0.25} \cdot \left|{2}^{0.25} \cdot x\right| \]

Alternative 2
Error	2.05%
Cost	19584

\[{\left(\sqrt[3]{2 \cdot x} \cdot \sqrt[3]{x}\right)}^{1.5} \]

Alternative 3
Error	0.6%
Cost	13252

\[\begin{array}{l} \mathbf{if}\;x \leq -5 \cdot 10^{-310}:\\ \;\;\;\;x \cdot \left(-\sqrt{2}\right)\\ \mathbf{else}:\\ \;\;\;\;\sqrt{2 \cdot x} \cdot \sqrt{x}\\ \end{array} \]

Alternative 4
Error	0.69%
Cost	6788

\[\begin{array}{l} \mathbf{if}\;x \leq -5 \cdot 10^{-310}:\\ \;\;\;\;x \cdot \left(-\sqrt{2}\right)\\ \mathbf{else}:\\ \;\;\;\;x \cdot \sqrt{2}\\ \end{array} \]

Alternative 5
Error	49.39%
Cost	6592

\[x \cdot \sqrt{2} \]

Reproduce

herbie shell --seed 2023104 
(FPCore (x)
  :name "sqrt B (should all be same)"
  :precision binary64
  (sqrt (* (* 2.0 x) x)))