Average Error: 0.2 → 0.2
Time: 5.6s
Precision: binary32
\[\left(10^{-5} \leq u \land u \leq 1\right) \land \left(0 \leq v \land v \leq 109.746574\right)\]
\[1 + v \cdot \log \left(u + \left(1 - u\right) \cdot e^{\frac{-2}{v}}\right) \]
↓
\[\mathsf{fma}\left(v, \log \left(u + e^{\frac{-2}{v} + \mathsf{log1p}\left(-u\right)}\right), 1\right) \]
(FPCore (u v)
 :precision binary32
 (+ 1.0 (* v (log (+ u (* (- 1.0 u) (exp (/ -2.0 v))))))))
↓
(FPCore (u v)
 :precision binary32
 (fma v (log (+ u (exp (+ (/ -2.0 v) (log1p (- u)))))) 1.0))
float code(float u, float v) {
	return 1.0f + (v * logf((u + ((1.0f - u) * expf((-2.0f / v))))));
}
↓
float code(float u, float v) {
	return fmaf(v, logf((u + expf(((-2.0f / v) + log1pf(-u))))), 1.0f);
}

function code(u, v)
	return Float32(Float32(1.0) + Float32(v * log(Float32(u + Float32(Float32(Float32(1.0) - u) * exp(Float32(Float32(-2.0) / v)))))))
end
↓
function code(u, v)
	return fma(v, log(Float32(u + exp(Float32(Float32(Float32(-2.0) / v) + log1p(Float32(-u)))))), Float32(1.0))
end

1 + v \cdot \log \left(u + \left(1 - u\right) \cdot e^{\frac{-2}{v}}\right)
↓
\mathsf{fma}\left(v, \log \left(u + e^{\frac{-2}{v} + \mathsf{log1p}\left(-u\right)}\right), 1\right)

Error

Bits error versus u

Bits error versus v

Derivation

  1. Initial program 0.2

    \[1 + v \cdot \log \left(u + \left(1 - u\right) \cdot e^{\frac{-2}{v}}\right) \]

  2. Simplified0.2

    \[\leadsto \color{blue}{\mathsf{fma}\left(v, \log \left(\mathsf{fma}\left(1 - u, e^{\frac{-2}{v}}, u\right)\right), 1\right)} \]

  3. Applied egg-rr0.2

    \[\leadsto \mathsf{fma}\left(v, \log \color{blue}{\left(u + e^{\frac{-2}{v}} \cdot \left(1 - u\right)\right)}, 1\right) \]

  4. Applied egg-rr0.2

    \[\leadsto \mathsf{fma}\left(v, \log \left(u + \color{blue}{e^{\left(\frac{-2}{v} + \mathsf{log1p}\left(-u\right)\right) \cdot 1}}\right), 1\right) \]

  5. Final simplification0.2

    \[\leadsto \mathsf{fma}\left(v, \log \left(u + e^{\frac{-2}{v} + \mathsf{log1p}\left(-u\right)}\right), 1\right) \]

Reproduce

herbie shell --seed 2022170 
(FPCore (u v)
  :name "HairBSDF, sample_f, cosTheta"
  :precision binary32
  :pre (and (and (<= 1e-5 u) (<= u 1.0)) (and (<= 0.0 v) (<= v 109.746574)))
  (+ 1.0 (* v (log (+ u (* (- 1.0 u) (exp (/ -2.0 v))))))))