HairBSDF, gamma for a refracted ray

Percentage Accurate: 92.2% → 98.4%

Time: 15.9s

Alternatives: 4

Speedup: 1.5×

Specification

\[\left(\left(-1 \leq sinTheta\_O \land sinTheta\_O \leq 1\right) \land \left(-1 \leq h \land h \leq 1\right)\right) \land \left(0 \leq eta \land eta \leq 10\right)\]

Math

\[\begin{array}{l} \\ \sin^{-1} \left(\frac{h}{\sqrt{eta \cdot eta - \frac{sinTheta\_O \cdot sinTheta\_O}{\sqrt{1 - sinTheta\_O \cdot sinTheta\_O}}}}\right) \end{array} \]

FPCore

(FPCore (sinTheta_O h eta)
 :precision binary32
 (asin
  (/
   h
   (sqrt
    (-
     (* eta eta)
     (/
      (* sinTheta_O sinTheta_O)
      (sqrt (- 1.0 (* sinTheta_O sinTheta_O)))))))))

C

float code(float sinTheta_O, float h, float eta) {
	return asinf((h / sqrtf(((eta * eta) - ((sinTheta_O * sinTheta_O) / sqrtf((1.0f - (sinTheta_O * sinTheta_O))))))));
}

Fortran

real(4) function code(sintheta_o, h, eta)
    real(4), intent (in) :: sintheta_o
    real(4), intent (in) :: h
    real(4), intent (in) :: eta
    code = asin((h / sqrt(((eta * eta) - ((sintheta_o * sintheta_o) / sqrt((1.0e0 - (sintheta_o * sintheta_o))))))))
end function

Julia

function code(sinTheta_O, h, eta)
	return asin(Float32(h / sqrt(Float32(Float32(eta * eta) - Float32(Float32(sinTheta_O * sinTheta_O) / sqrt(Float32(Float32(1.0) - Float32(sinTheta_O * sinTheta_O))))))))
end

MATLAB

function tmp = code(sinTheta_O, h, eta)
	tmp = asin((h / sqrt(((eta * eta) - ((sinTheta_O * sinTheta_O) / sqrt((single(1.0) - (sinTheta_O * sinTheta_O))))))));
end

Initial Program: 92.2% accurate, 1.0× speedup

Math

\[\begin{array}{l} \\ \sin^{-1} \left(\frac{h}{\sqrt{eta \cdot eta - \frac{sinTheta\_O \cdot sinTheta\_O}{\sqrt{1 - sinTheta\_O \cdot sinTheta\_O}}}}\right) \end{array} \]

FPCore

(FPCore (sinTheta_O h eta)
 :precision binary32
 (asin
  (/
   h
   (sqrt
    (-
     (* eta eta)
     (/
      (* sinTheta_O sinTheta_O)
      (sqrt (- 1.0 (* sinTheta_O sinTheta_O)))))))))

C

float code(float sinTheta_O, float h, float eta) {
	return asinf((h / sqrtf(((eta * eta) - ((sinTheta_O * sinTheta_O) / sqrtf((1.0f - (sinTheta_O * sinTheta_O))))))));
}

Fortran

real(4) function code(sintheta_o, h, eta)
    real(4), intent (in) :: sintheta_o
    real(4), intent (in) :: h
    real(4), intent (in) :: eta
    code = asin((h / sqrt(((eta * eta) - ((sintheta_o * sintheta_o) / sqrt((1.0e0 - (sintheta_o * sintheta_o))))))))
end function

Julia

function code(sinTheta_O, h, eta)
	return asin(Float32(h / sqrt(Float32(Float32(eta * eta) - Float32(Float32(sinTheta_O * sinTheta_O) / sqrt(Float32(Float32(1.0) - Float32(sinTheta_O * sinTheta_O))))))))
end

MATLAB

function tmp = code(sinTheta_O, h, eta)
	tmp = asin((h / sqrt(((eta * eta) - ((sinTheta_O * sinTheta_O) / sqrt((single(1.0) - (sinTheta_O * sinTheta_O))))))));
end

Alternative 1: 98.4% accurate, 1.1× speedup

Math

\[\begin{array}{l} \\ \sin^{-1} \left(\frac{h}{\sqrt{eta - sinTheta\_O} \cdot \sqrt{eta + sinTheta\_O}}\right) \end{array} \]

FPCore

(FPCore (sinTheta_O h eta)
 :precision binary32
 (asin (/ h (* (sqrt (- eta sinTheta_O)) (sqrt (+ eta sinTheta_O))))))

C

float code(float sinTheta_O, float h, float eta) {
	return asinf((h / (sqrtf((eta - sinTheta_O)) * sqrtf((eta + sinTheta_O)))));
}

Fortran

real(4) function code(sintheta_o, h, eta)
    real(4), intent (in) :: sintheta_o
    real(4), intent (in) :: h
    real(4), intent (in) :: eta
    code = asin((h / (sqrt((eta - sintheta_o)) * sqrt((eta + sintheta_o)))))
end function

Julia

function code(sinTheta_O, h, eta)
	return asin(Float32(h / Float32(sqrt(Float32(eta - sinTheta_O)) * sqrt(Float32(eta + sinTheta_O)))))
end

MATLAB

function tmp = code(sinTheta_O, h, eta)
	tmp = asin((h / (sqrt((eta - sinTheta_O)) * sqrt((eta + sinTheta_O)))));
end

Derivation

1. Initial program 92.2%

   \[\sin^{-1} \left(\frac{h}{\sqrt{eta \cdot eta - \frac{sinTheta\_O \cdot sinTheta\_O}{\sqrt{1 - sinTheta\_O \cdot sinTheta\_O}}}}\right) \]
2. Add Preprocessing

3. Taylor expanded in sinTheta_O around 0

   \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{-1 \cdot {sinTheta\_O}^{2} + {eta}^{2}}}}\right) \]
4. Step-by-step derivation

   1. +-commutative N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{{eta}^{2} + -1 \cdot {sinTheta\_O}^{2}}}}\right) \]

   2. mul-1-neg N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{{eta}^{2} + \color{blue}{\left(\mathsf{neg}\left({sinTheta\_O}^{2}\right)\right)}}}\right) \]

   3. unsub-neg N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{{eta}^{2} - {sinTheta\_O}^{2}}}}\right) \]

   4. unpow2 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{eta \cdot eta} - {sinTheta\_O}^{2}}}\right) \]

   5. unpow2 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{eta \cdot eta - \color{blue}{sinTheta\_O \cdot sinTheta\_O}}}\right) \]

   6. difference-of-squares N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{\left(eta + sinTheta\_O\right) \cdot \left(eta - sinTheta\_O\right)}}}\right) \]

   7. lower-*.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{\left(eta + sinTheta\_O\right) \cdot \left(eta - sinTheta\_O\right)}}}\right) \]

   8. lower-+.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{\left(eta + sinTheta\_O\right)} \cdot \left(eta - sinTheta\_O\right)}}\right) \]

   9. lower--.f32 92.2

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\left(eta + sinTheta\_O\right) \cdot \color{blue}{\left(eta - sinTheta\_O\right)}}}\right) \]

5. Simplified 92.2%

   \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{\left(eta + sinTheta\_O\right) \cdot \left(eta - sinTheta\_O\right)}}}\right) \]
6. Step-by-step derivation

   1. lift-+.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{\left(eta + sinTheta\_O\right)} \cdot \left(eta - sinTheta\_O\right)}}\right) \]

   2. lift--.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\left(eta + sinTheta\_O\right) \cdot \color{blue}{\left(eta - sinTheta\_O\right)}}}\right) \]

   3. *-commutative N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{\color{blue}{\left(eta - sinTheta\_O\right) \cdot \left(eta + sinTheta\_O\right)}}}\right) \]

   4. sqrt-prod N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\sqrt{eta - sinTheta\_O} \cdot \sqrt{eta + sinTheta\_O}}}\right) \]

   5. pow1/2 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{{\left(eta - sinTheta\_O\right)}^{\frac{1}{2}}} \cdot \sqrt{eta + sinTheta\_O}}\right) \]

   6. pow1/2 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{{\left(eta - sinTheta\_O\right)}^{\frac{1}{2}} \cdot \color{blue}{{\left(eta + sinTheta\_O\right)}^{\frac{1}{2}}}}\right) \]

   7. lower-*.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{{\left(eta - sinTheta\_O\right)}^{\frac{1}{2}} \cdot {\left(eta + sinTheta\_O\right)}^{\frac{1}{2}}}}\right) \]

   8. pow1/2 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\sqrt{eta - sinTheta\_O}} \cdot {\left(eta + sinTheta\_O\right)}^{\frac{1}{2}}}\right) \]

   9. lower-sqrt.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\sqrt{eta - sinTheta\_O}} \cdot {\left(eta + sinTheta\_O\right)}^{\frac{1}{2}}}\right) \]

   10. pow1/2 N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{eta - sinTheta\_O} \cdot \color{blue}{\sqrt{eta + sinTheta\_O}}}\right) \]

   11. lower-sqrt.f32 98.5

       \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{eta - sinTheta\_O} \cdot \color{blue}{\sqrt{eta + sinTheta\_O}}}\right) \]

   12. lift-+.f32 N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{eta - sinTheta\_O} \cdot \sqrt{\color{blue}{eta + sinTheta\_O}}}\right) \]

   13. +-commutative N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{eta - sinTheta\_O} \cdot \sqrt{\color{blue}{sinTheta\_O + eta}}}\right) \]

   14. lower-+.f32 98.5

       \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{eta - sinTheta\_O} \cdot \sqrt{\color{blue}{sinTheta\_O + eta}}}\right) \]

7. Applied egg-rr 98.5%

   \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\sqrt{eta - sinTheta\_O} \cdot \sqrt{sinTheta\_O + eta}}}\right) \]

8. Final simplification 98.5%

   \[\leadsto \sin^{-1} \left(\frac{h}{\sqrt{eta - sinTheta\_O} \cdot \sqrt{eta + sinTheta\_O}}\right) \]
9. Add Preprocessing

Alternative 2: 97.9% accurate, 1.2× speedup

Math

\[\begin{array}{l} \\ \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(\frac{sinTheta\_O \cdot -0.5}{eta}, sinTheta\_O, eta\right)}\right) \end{array} \]

FPCore

(FPCore (sinTheta_O h eta)
 :precision binary32
 (asin (/ h (fma (/ (* sinTheta_O -0.5) eta) sinTheta_O eta))))

C

float code(float sinTheta_O, float h, float eta) {
	return asinf((h / fmaf(((sinTheta_O * -0.5f) / eta), sinTheta_O, eta)));
}

Julia

function code(sinTheta_O, h, eta)
	return asin(Float32(h / fma(Float32(Float32(sinTheta_O * Float32(-0.5)) / eta), sinTheta_O, eta)))
end

Derivation

1. Initial program 92.2%

   \[\sin^{-1} \left(\frac{h}{\sqrt{eta \cdot eta - \frac{sinTheta\_O \cdot sinTheta\_O}{\sqrt{1 - sinTheta\_O \cdot sinTheta\_O}}}}\right) \]
2. Add Preprocessing

3. Taylor expanded in sinTheta_O around 0

   \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{eta + \frac{-1}{2} \cdot \frac{{sinTheta\_O}^{2}}{eta}}}\right) \]
4. Step-by-step derivation

   1. +-commutative N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\frac{-1}{2} \cdot \frac{{sinTheta\_O}^{2}}{eta} + eta}}\right) \]

   2. associate-*r/ N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\frac{\frac{-1}{2} \cdot {sinTheta\_O}^{2}}{eta}} + eta}\right) \]

   3. *-commutative N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\frac{\color{blue}{{sinTheta\_O}^{2} \cdot \frac{-1}{2}}}{eta} + eta}\right) \]

   4. associate-/l* N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{{sinTheta\_O}^{2} \cdot \frac{\frac{-1}{2}}{eta}} + eta}\right) \]

   5. metadata-eval N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{{sinTheta\_O}^{2} \cdot \frac{\color{blue}{\mathsf{neg}\left(\frac{1}{2}\right)}}{eta} + eta}\right) \]

   6. distribute-neg-frac N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{{sinTheta\_O}^{2} \cdot \color{blue}{\left(\mathsf{neg}\left(\frac{\frac{1}{2}}{eta}\right)\right)} + eta}\right) \]

   7. metadata-eval N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{{sinTheta\_O}^{2} \cdot \left(\mathsf{neg}\left(\frac{\color{blue}{\frac{1}{2} \cdot 1}}{eta}\right)\right) + eta}\right) \]

   8. associate-*r/ N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{{sinTheta\_O}^{2} \cdot \left(\mathsf{neg}\left(\color{blue}{\frac{1}{2} \cdot \frac{1}{eta}}\right)\right) + eta}\right) \]

   9. lower-fma.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\mathsf{fma}\left({sinTheta\_O}^{2}, \mathsf{neg}\left(\frac{1}{2} \cdot \frac{1}{eta}\right), eta\right)}}\right) \]

   10. unpow2 N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(\color{blue}{sinTheta\_O \cdot sinTheta\_O}, \mathsf{neg}\left(\frac{1}{2} \cdot \frac{1}{eta}\right), eta\right)}\right) \]

   11. lower-*.f32 N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(\color{blue}{sinTheta\_O \cdot sinTheta\_O}, \mathsf{neg}\left(\frac{1}{2} \cdot \frac{1}{eta}\right), eta\right)}\right) \]

   12. associate-*r/ N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \mathsf{neg}\left(\color{blue}{\frac{\frac{1}{2} \cdot 1}{eta}}\right), eta\right)}\right) \]

   13. metadata-eval N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \mathsf{neg}\left(\frac{\color{blue}{\frac{1}{2}}}{eta}\right), eta\right)}\right) \]

   14. distribute-neg-frac N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \color{blue}{\frac{\mathsf{neg}\left(\frac{1}{2}\right)}{eta}}, eta\right)}\right) \]

   15. metadata-eval N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \frac{\color{blue}{\frac{-1}{2}}}{eta}, eta\right)}\right) \]

   16. lower-/.f32 97.4

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \color{blue}{\frac{-0.5}{eta}}, eta\right)}\right) \]

5. Simplified 97.4%

   \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \frac{-0.5}{eta}, eta\right)}}\right) \]
6. Step-by-step derivation

   1. lift-*.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\left(sinTheta\_O \cdot sinTheta\_O\right)} \cdot \frac{\frac{-1}{2}}{eta} + eta}\right) \]

   2. lift-/.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\left(sinTheta\_O \cdot sinTheta\_O\right) \cdot \color{blue}{\frac{\frac{-1}{2}}{eta}} + eta}\right) \]

   3. lift-*.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\left(sinTheta\_O \cdot sinTheta\_O\right)} \cdot \frac{\frac{-1}{2}}{eta} + eta}\right) \]

   4. associate-*l* N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{sinTheta\_O \cdot \left(sinTheta\_O \cdot \frac{\frac{-1}{2}}{eta}\right)} + eta}\right) \]

   5. *-commutative N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\left(sinTheta\_O \cdot \frac{\frac{-1}{2}}{eta}\right) \cdot sinTheta\_O} + eta}\right) \]

   6. lower-fma.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\mathsf{fma}\left(sinTheta\_O \cdot \frac{\frac{-1}{2}}{eta}, sinTheta\_O, eta\right)}}\right) \]

   7. lift-/.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot \color{blue}{\frac{\frac{-1}{2}}{eta}}, sinTheta\_O, eta\right)}\right) \]

   8. associate-*r/ N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(\color{blue}{\frac{sinTheta\_O \cdot \frac{-1}{2}}{eta}}, sinTheta\_O, eta\right)}\right) \]

   9. lift-*.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(\frac{\color{blue}{sinTheta\_O \cdot \frac{-1}{2}}}{eta}, sinTheta\_O, eta\right)}\right) \]

   10. lower-/.f32 98.1

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(\color{blue}{\frac{sinTheta\_O \cdot -0.5}{eta}}, sinTheta\_O, eta\right)}\right) \]

7. Applied egg-rr 98.1%

   \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\mathsf{fma}\left(\frac{sinTheta\_O \cdot -0.5}{eta}, sinTheta\_O, eta\right)}}\right) \]
8. Add Preprocessing

Alternative 3: 97.4% accurate, 1.2× speedup

Math

\[\begin{array}{l} \\ \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \frac{-0.5}{eta}, eta\right)}\right) \end{array} \]

FPCore

(FPCore (sinTheta_O h eta)
 :precision binary32
 (asin (/ h (fma (* sinTheta_O sinTheta_O) (/ -0.5 eta) eta))))

C

float code(float sinTheta_O, float h, float eta) {
	return asinf((h / fmaf((sinTheta_O * sinTheta_O), (-0.5f / eta), eta)));
}

Julia

function code(sinTheta_O, h, eta)
	return asin(Float32(h / fma(Float32(sinTheta_O * sinTheta_O), Float32(Float32(-0.5) / eta), eta)))
end

Derivation

1. Initial program 92.2%

   \[\sin^{-1} \left(\frac{h}{\sqrt{eta \cdot eta - \frac{sinTheta\_O \cdot sinTheta\_O}{\sqrt{1 - sinTheta\_O \cdot sinTheta\_O}}}}\right) \]
2. Add Preprocessing

3. Taylor expanded in sinTheta_O around 0

   \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{eta + \frac{-1}{2} \cdot \frac{{sinTheta\_O}^{2}}{eta}}}\right) \]
4. Step-by-step derivation

   1. +-commutative N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\frac{-1}{2} \cdot \frac{{sinTheta\_O}^{2}}{eta} + eta}}\right) \]

   2. associate-*r/ N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\frac{\frac{-1}{2} \cdot {sinTheta\_O}^{2}}{eta}} + eta}\right) \]

   3. *-commutative N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\frac{\color{blue}{{sinTheta\_O}^{2} \cdot \frac{-1}{2}}}{eta} + eta}\right) \]

   4. associate-/l* N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{{sinTheta\_O}^{2} \cdot \frac{\frac{-1}{2}}{eta}} + eta}\right) \]

   5. metadata-eval N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{{sinTheta\_O}^{2} \cdot \frac{\color{blue}{\mathsf{neg}\left(\frac{1}{2}\right)}}{eta} + eta}\right) \]

   6. distribute-neg-frac N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{{sinTheta\_O}^{2} \cdot \color{blue}{\left(\mathsf{neg}\left(\frac{\frac{1}{2}}{eta}\right)\right)} + eta}\right) \]

   7. metadata-eval N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{{sinTheta\_O}^{2} \cdot \left(\mathsf{neg}\left(\frac{\color{blue}{\frac{1}{2} \cdot 1}}{eta}\right)\right) + eta}\right) \]

   8. associate-*r/ N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{{sinTheta\_O}^{2} \cdot \left(\mathsf{neg}\left(\color{blue}{\frac{1}{2} \cdot \frac{1}{eta}}\right)\right) + eta}\right) \]

   9. lower-fma.f32 N/A

      \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\mathsf{fma}\left({sinTheta\_O}^{2}, \mathsf{neg}\left(\frac{1}{2} \cdot \frac{1}{eta}\right), eta\right)}}\right) \]

   10. unpow2 N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(\color{blue}{sinTheta\_O \cdot sinTheta\_O}, \mathsf{neg}\left(\frac{1}{2} \cdot \frac{1}{eta}\right), eta\right)}\right) \]

   11. lower-*.f32 N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(\color{blue}{sinTheta\_O \cdot sinTheta\_O}, \mathsf{neg}\left(\frac{1}{2} \cdot \frac{1}{eta}\right), eta\right)}\right) \]

   12. associate-*r/ N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \mathsf{neg}\left(\color{blue}{\frac{\frac{1}{2} \cdot 1}{eta}}\right), eta\right)}\right) \]

   13. metadata-eval N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \mathsf{neg}\left(\frac{\color{blue}{\frac{1}{2}}}{eta}\right), eta\right)}\right) \]

   14. distribute-neg-frac N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \color{blue}{\frac{\mathsf{neg}\left(\frac{1}{2}\right)}{eta}}, eta\right)}\right) \]

   15. metadata-eval N/A

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \frac{\color{blue}{\frac{-1}{2}}}{eta}, eta\right)}\right) \]

   16. lower-/.f32 97.4

       \[\leadsto \sin^{-1} \left(\frac{h}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \color{blue}{\frac{-0.5}{eta}}, eta\right)}\right) \]

5. Simplified 97.4%

   \[\leadsto \sin^{-1} \left(\frac{h}{\color{blue}{\mathsf{fma}\left(sinTheta\_O \cdot sinTheta\_O, \frac{-0.5}{eta}, eta\right)}}\right) \]
6. Add Preprocessing

Alternative 4: 95.6% accurate, 1.5× speedup

Math

\[\begin{array}{l} \\ \sin^{-1} \left(\frac{h}{eta}\right) \end{array} \]

FPCore

(FPCore (sinTheta_O h eta) :precision binary32 (asin (/ h eta)))

C

float code(float sinTheta_O, float h, float eta) {
	return asinf((h / eta));
}

Fortran

real(4) function code(sintheta_o, h, eta)
    real(4), intent (in) :: sintheta_o
    real(4), intent (in) :: h
    real(4), intent (in) :: eta
    code = asin((h / eta))
end function

Julia

function code(sinTheta_O, h, eta)
	return asin(Float32(h / eta))
end

MATLAB

function tmp = code(sinTheta_O, h, eta)
	tmp = asin((h / eta));
end

Derivation

1. Initial program 92.2%

   \[\sin^{-1} \left(\frac{h}{\sqrt{eta \cdot eta - \frac{sinTheta\_O \cdot sinTheta\_O}{\sqrt{1 - sinTheta\_O \cdot sinTheta\_O}}}}\right) \]
2. Add Preprocessing

3. Taylor expanded in eta around inf

   \[\leadsto \sin^{-1} \color{blue}{\left(\frac{h}{eta}\right)} \]
4. Step-by-step derivation

   1. lower-/.f32 96.0

      \[\leadsto \sin^{-1} \color{blue}{\left(\frac{h}{eta}\right)} \]

5. Simplified 96.0%

   \[\leadsto \sin^{-1} \color{blue}{\left(\frac{h}{eta}\right)} \]
6. Add Preprocessing

Reproduce

herbie shell --seed 2024207 
(FPCore (sinTheta_O h eta)
  :name "HairBSDF, gamma for a refracted ray"
  :precision binary32
  :pre (and (and (and (<= -1.0 sinTheta_O) (<= sinTheta_O 1.0)) (and (<= -1.0 h) (<= h 1.0))) (and (<= 0.0 eta) (<= eta 10.0)))
  (asin (/ h (sqrt (- (* eta eta) (/ (* sinTheta_O sinTheta_O) (sqrt (- 1.0 (* sinTheta_O sinTheta_O)))))))))