Use FastExp() more

src/pbrt/bssrdf.cpp

@@ -57,19 +57,18 @@ Float BeamDiffusionMS(Float sigma_s, Float sigma_a, Float g, Float eta, Float r)
         Float dr = std::sqrt(r * r + zr * zr), dv = std::sqrt(r * r + zv * zv);
         // Compute dipole fluence rate $\dipole(r)$ using Equation
         // $(\ref{eq:diffusion-dipole})$
-        Float phiD = Inv4Pi / D_g *
-                     (std::exp(-sigma_tr * dr) / dr - std::exp(-sigma_tr * dv) / dv);
+        Float phiD =
+            Inv4Pi / D_g * (FastExp(-sigma_tr * dr) / dr - FastExp(-sigma_tr * dv) / dv);
 
         // Compute dipole vector irradiance $-\N{}\cdot\dipoleE(r)$ using Equation
         // $(\ref{eq:diffusion-dipole-vector-irradiance-normal})$
-        Float EDn =
-            Inv4Pi *
-            (zr * (1 + sigma_tr * dr) * std::exp(-sigma_tr * dr) / (dr * dr * dr) -
-             zv * (1 + sigma_tr * dv) * std::exp(-sigma_tr * dv) / (dv * dv * dv));
+        Float EDn = Inv4Pi *
+                    (zr * (1 + sigma_tr * dr) * FastExp(-sigma_tr * dr) / (dr * dr * dr) -
+                     zv * (1 + sigma_tr * dv) * FastExp(-sigma_tr * dv) / (dv * dv * dv));
 
         // Add contribution from dipole for depth $\depthreal$ to _Ed_
         Float E = phiD * cPhi + EDn * cE;
-        Float kappa = 1 - std::exp(-2 * sigmap_t * (dr + zr));
+        Float kappa = 1 - FastExp(-2 * sigmap_t * (dr + zr));
         Ed += kappa * rhop * rhop * E;
     }
     return Ed / nSamples;
@@ -90,7 +89,7 @@ Float BeamDiffusionSS(Float sigma_s, Float sigma_a, Float g, Float eta, Float r)
         Float cosTheta_o = ti / d;
 
         // Add contribution of single scattering at depth $t$
-        Ess += rho * std::exp(-sigma_t * (d + tCrit)) / (d * d) *
+        Ess += rho * FastExp(-sigma_t * (d + tCrit)) / (d * d) *
                HenyeyGreenstein(cosTheta_o, g) * (1 - FrDielectric(-cosTheta_o, eta)) *
                std::abs(cosTheta_o);
     }
@@ -106,8 +105,8 @@ void ComputeBeamDiffusionBSSRDF(Float g, Float eta, BSSRDFTable *t) {
 
     // Choose albedo values of the diffusion profile discretization
     for (int i = 0; i < t->rhoSamples.size(); ++i)
-        t->rhoSamples[i] = (1 - std::exp(-8 * i / (Float)(t->rhoSamples.size() - 1))) /
-                           (1 - std::exp(-8));
+        t->rhoSamples[i] =
+            (1 - FastExp(-8 * i / (Float)(t->rhoSamples.size() - 1))) / (1 - FastExp(-8));
 
     ParallelFor(0, t->rhoSamples.size(), [&](int i) {
         // Compute the diffusion profile for the _i_th albedo sample

src/pbrt/bxdfs.cpp

@@ -455,7 +455,7 @@ pstd::optional<BSDFSample> HairBxDF::Sample_f(Vector3f wo, Float uc, Point2f u,
 
     // Sample $M_p$ to compute $\thetai$
     Float cosTheta = 1 + v[p] * std::log(std::max<Float>(u[0], 1e-5) +
-                                         (1 - u[0]) * std::exp(-2 / v[p]));
+                                         (1 - u[0]) * FastExp(-2 / v[p]));
     Float sinTheta = SafeSqrt(1 - Sqr(cosTheta));
     Float cosPhi = std::cos(2 * Pi * u[1]);
     Float sinTheta_i = -cosTheta * sinThetap_o + sinTheta * cosPhi * cosThetap_o;

src/pbrt/bxdfs.h

@@ -923,7 +923,7 @@ class LayeredBxDF {
     static Float Tr(Float dz, const Vector3f &w) {
         if (std::abs(dz) <= std::numeric_limits<Float>::min())
             return 1;
-        return std::exp(-std::abs(dz / w.z));
+        return FastExp(-std::abs(dz / w.z));
     }
 
     // LayeredBxDF Protected Members
@@ -1000,9 +1000,9 @@ class HairBxDF {
                     Float sinTheta_o, Float v) {
         Float a = cosTheta_i * cosTheta_o / v;
         Float b = sinTheta_i * sinTheta_o / v;
-        Float mp =
-            (v <= .1) ? (std::exp(LogI0(a) - b - 1 / v + 0.6931f + std::log(1 / (2 * v))))
-                      : (std::exp(-b) * I0(a)) / (std::sinh(1 / v) * 2 * v);
+        Float mp = (v <= .1)
+                       ? (FastExp(LogI0(a) - b - 1 / v + 0.6931f + std::log(1 / (2 * v))))
+                       : (FastExp(-b) * I0(a)) / (std::sinh(1 / v) * 2 * v);
         CHECK(!IsInf(mp) && !IsNaN(mp));
         return mp;
     }

src/pbrt/util/spectrum.h

@@ -72,7 +72,7 @@ PBRT_CPU_GPU inline Float Blackbody(Float lambda, Float T) {
     const Float kb = 1.3806488e-23;
     // Return emitted radiance for blackbody at wavelength _lambda[i]_
     Float l = lambda * 1e-9f;
-    Float Le = (2 * h * c * c) / (Pow<5>(l) * (std::exp((h * c) / (l * kb * T)) - 1));
+    Float Le = (2 * h * c * c) / (Pow<5>(l) * (FastExp((h * c) / (l * kb * T)) - 1));
     CHECK(!IsNaN(Le));
     return Le;
 }

src/pbrt/util/spectrum_test.cpp

@@ -41,7 +41,7 @@ TEST(Spectrum, Blackbody) {
     // consistent with this.
     for (Float T : {2700, 3000, 4500, 5600, 6000}) {
         Float lambdaMax = 2.8977721e-3 / T * 1e9;
-        Float lambda[3] = {Float(.999 * lambdaMax), lambdaMax, Float(1.001 * lambdaMax)};
+        Float lambda[3] = {Float(.99 * lambdaMax), lambdaMax, Float(1.01 * lambdaMax)};
         EXPECT_LT(Blackbody(lambda[0], T), Blackbody(lambda[1], T));
         EXPECT_GT(Blackbody(lambda[1], T), Blackbody(lambda[2], T));
     }