Rust f32::acosh

Percentage Accurate: 52.3% → 98.1%
Time: 3.9s
Alternatives: 3
Speedup: 2.0×

Specification

?
\[x \geq 1\]
\[\begin{array}{l} \\ \cosh^{-1} x \end{array} \]
(FPCore (x) :precision binary32 (acosh x))
float code(float x) {
	return acoshf(x);
}

function code(x)
	return acosh(x)
end

function tmp = code(x)
	tmp = acosh(x);
end

\begin{array}{l}

\\
\cosh^{-1} x
\end{array}

Sampling outcomes in binary32 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 3 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: 52.3% accurate, 1.0× speedup?

\[\begin{array}{l} \\ \log \left(x + \sqrt{x \cdot x - 1}\right) \end{array} \]
(FPCore (x) :precision binary32 (log (+ x (sqrt (- (* x x) 1.0)))))
float code(float x) {
	return logf((x + sqrtf(((x * x) - 1.0f))));
}

real(4) function code(x)
    real(4), intent (in) :: x
    code = log((x + sqrt(((x * x) - 1.0e0))))
end function

function code(x)
	return log(Float32(x + sqrt(Float32(Float32(x * x) - Float32(1.0)))))
end

function tmp = code(x)
	tmp = log((x + sqrt(((x * x) - single(1.0)))));
end

\begin{array}{l}

\\
\log \left(x + \sqrt{x \cdot x - 1}\right)
\end{array}

Alternative 1: 98.1% accurate, 1.9× speedup?

\[\begin{array}{l} \\ \mathsf{log1p}\left(x \cdot \left(2 + \frac{-1 + \frac{-0.5}{x}}{x}\right)\right) \end{array} \]
(FPCore (x)
 :precision binary32
 (log1p (* x (+ 2.0 (/ (+ -1.0 (/ -0.5 x)) x)))))
float code(float x) {
	return log1pf((x * (2.0f + ((-1.0f + (-0.5f / x)) / x))));
}

function code(x)
	return log1p(Float32(x * Float32(Float32(2.0) + Float32(Float32(Float32(-1.0) + Float32(Float32(-0.5) / x)) / x))))
end

\begin{array}{l}

\\
\mathsf{log1p}\left(x \cdot \left(2 + \frac{-1 + \frac{-0.5}{x}}{x}\right)\right)
\end{array}
Derivation

  1. Initial program 52.5%

    \[\log \left(x + \sqrt{x \cdot x - 1}\right) \]
  2. Add Preprocessing
  3. Step-by-step derivation

    1. log1p-expm1-u52.5%

      \[\leadsto \color{blue}{\mathsf{log1p}\left(\mathsf{expm1}\left(\log \left(x + \sqrt{x \cdot x - 1}\right)\right)\right)} \]

    2. expm1-undefine52.5%

      \[\leadsto \mathsf{log1p}\left(\color{blue}{e^{\log \left(x + \sqrt{x \cdot x - 1}\right)} - 1}\right) \]

    3. add-exp-log52.5%

      \[\leadsto \mathsf{log1p}\left(\color{blue}{\left(x + \sqrt{x \cdot x - 1}\right)} - 1\right) \]

    4. fma-neg52.5%

      \[\leadsto \mathsf{log1p}\left(\left(x + \sqrt{\color{blue}{\mathsf{fma}\left(x, x, -1\right)}}\right) - 1\right) \]

    5. metadata-eval52.5%

      \[\leadsto \mathsf{log1p}\left(\left(x + \sqrt{\mathsf{fma}\left(x, x, \color{blue}{-1}\right)}\right) - 1\right) \]

  4. Applied egg-rr52.5%

    \[\leadsto \color{blue}{\mathsf{log1p}\left(\left(x + \sqrt{\mathsf{fma}\left(x, x, -1\right)}\right) - 1\right)} \]

  5. Taylor expanded in x around inf 99.1%

    \[\leadsto \mathsf{log1p}\left(\color{blue}{x \cdot \left(2 + -1 \cdot \frac{1 + 0.5 \cdot \frac{1}{x}}{x}\right)}\right) \]
  6. Step-by-step derivation

    1. associate-*r/99.1%

      \[\leadsto \mathsf{log1p}\left(x \cdot \left(2 + \color{blue}{\frac{-1 \cdot \left(1 + 0.5 \cdot \frac{1}{x}\right)}{x}}\right)\right) \]

    2. associate-*r/99.1%

      \[\leadsto \mathsf{log1p}\left(x \cdot \left(2 + \frac{-1 \cdot \left(1 + \color{blue}{\frac{0.5 \cdot 1}{x}}\right)}{x}\right)\right) \]

    3. metadata-eval99.1%

      \[\leadsto \mathsf{log1p}\left(x \cdot \left(2 + \frac{-1 \cdot \left(1 + \frac{\color{blue}{0.5}}{x}\right)}{x}\right)\right) \]

    4. distribute-lft-in99.1%

      \[\leadsto \mathsf{log1p}\left(x \cdot \left(2 + \frac{\color{blue}{-1 \cdot 1 + -1 \cdot \frac{0.5}{x}}}{x}\right)\right) \]

    5. metadata-eval99.1%

      \[\leadsto \mathsf{log1p}\left(x \cdot \left(2 + \frac{\color{blue}{-1} + -1 \cdot \frac{0.5}{x}}{x}\right)\right) \]

    6. associate-*r/99.1%

      \[\leadsto \mathsf{log1p}\left(x \cdot \left(2 + \frac{-1 + \color{blue}{\frac{-1 \cdot 0.5}{x}}}{x}\right)\right) \]

    7. metadata-eval99.1%

      \[\leadsto \mathsf{log1p}\left(x \cdot \left(2 + \frac{-1 + \frac{\color{blue}{-0.5}}{x}}{x}\right)\right) \]

  7. Simplified99.1%

    \[\leadsto \mathsf{log1p}\left(\color{blue}{x \cdot \left(2 + \frac{-1 + \frac{-0.5}{x}}{x}\right)}\right) \]
  8. Add Preprocessing

Alternative 2: 96.7% accurate, 2.0× speedup?

\[\begin{array}{l} \\ \log \left(x + x\right) \end{array} \]
(FPCore (x) :precision binary32 (log (+ x x)))
float code(float x) {
	return logf((x + x));
}

real(4) function code(x)
    real(4), intent (in) :: x
    code = log((x + x))
end function

function code(x)
	return log(Float32(x + x))
end

function tmp = code(x)
	tmp = log((x + x));
end

\begin{array}{l}

\\
\log \left(x + x\right)
\end{array}
Derivation

  1. Initial program 52.5%

    \[\log \left(x + \sqrt{x \cdot x - 1}\right) \]
  2. Add Preprocessing

  3. Taylor expanded in x around inf 97.8%

    \[\leadsto \log \left(x + \color{blue}{x}\right) \]
  4. Add Preprocessing

Alternative 3: 1.3% accurate, 2.0× speedup?

\[\begin{array}{l} \\ \mathsf{log1p}\left(-1\right) \end{array} \]
(FPCore (x) :precision binary32 (log1p -1.0))
float code(float x) {
	return log1pf(-1.0f);
}

function code(x)
	return log1p(Float32(-1.0))
end

\begin{array}{l}

\\
\mathsf{log1p}\left(-1\right)
\end{array}
Derivation

  1. Initial program 52.5%

    \[\log \left(x + \sqrt{x \cdot x - 1}\right) \]
  2. Add Preprocessing
  3. Step-by-step derivation

    1. log1p-expm1-u52.5%

      \[\leadsto \color{blue}{\mathsf{log1p}\left(\mathsf{expm1}\left(\log \left(x + \sqrt{x \cdot x - 1}\right)\right)\right)} \]

    2. expm1-undefine52.5%

      \[\leadsto \mathsf{log1p}\left(\color{blue}{e^{\log \left(x + \sqrt{x \cdot x - 1}\right)} - 1}\right) \]

    3. add-exp-log52.5%

      \[\leadsto \mathsf{log1p}\left(\color{blue}{\left(x + \sqrt{x \cdot x - 1}\right)} - 1\right) \]

    4. fma-neg52.5%

      \[\leadsto \mathsf{log1p}\left(\left(x + \sqrt{\color{blue}{\mathsf{fma}\left(x, x, -1\right)}}\right) - 1\right) \]

    5. metadata-eval52.5%

      \[\leadsto \mathsf{log1p}\left(\left(x + \sqrt{\mathsf{fma}\left(x, x, \color{blue}{-1}\right)}\right) - 1\right) \]

  4. Applied egg-rr52.5%

    \[\leadsto \color{blue}{\mathsf{log1p}\left(\left(x + \sqrt{\mathsf{fma}\left(x, x, -1\right)}\right) - 1\right)} \]

  5. Taylor expanded in x around -inf 1.3%

    \[\leadsto \mathsf{log1p}\left(\color{blue}{-1}\right) \]
  6. Add Preprocessing

Developer target: 99.2% accurate, 0.7× speedup?

\[\begin{array}{l} \\ \log \left(x + \sqrt{x - 1} \cdot \sqrt{x + 1}\right) \end{array} \]
(FPCore (x)
 :precision binary32
 (log (+ x (* (sqrt (- x 1.0)) (sqrt (+ x 1.0))))))
float code(float x) {
	return logf((x + (sqrtf((x - 1.0f)) * sqrtf((x + 1.0f)))));
}

real(4) function code(x)
    real(4), intent (in) :: x
    code = log((x + (sqrt((x - 1.0e0)) * sqrt((x + 1.0e0)))))
end function

function code(x)
	return log(Float32(x + Float32(sqrt(Float32(x - Float32(1.0))) * sqrt(Float32(x + Float32(1.0))))))
end

function tmp = code(x)
	tmp = log((x + (sqrt((x - single(1.0))) * sqrt((x + single(1.0))))));
end

\begin{array}{l}

\\
\log \left(x + \sqrt{x - 1} \cdot \sqrt{x + 1}\right)
\end{array}

Reproduce

?
herbie shell --seed 2024087 
(FPCore (x)
  :name "Rust f32::acosh"
  :precision binary32
  :pre (>= x 1.0)

  :alt
  (log (+ x (* (sqrt (- x 1.0)) (sqrt (+ x 1.0)))))

  (log (+ x (sqrt (- (* x x) 1.0)))))