replaced some std::log/exp calls by the math::fastlog/exp equivalent

src/integrators/pssmlt/pssmlt_sampler.cpp

@@ -50,7 +50,7 @@ void PSSMLTSampler::serialize(Stream *stream, InstanceManager *manager) const {
 }
 
 void PSSMLTSampler::configure() {
-	m_logRatio = -std::log(m_s2/m_s1);
+	m_logRatio = -math::fastlog(m_s2/m_s1);
 	m_time = 0;
 	m_largeStepTime = 0;
 	m_largeStep = false;

src/libcore/warp.cpp

@@ -137,7 +137,7 @@ Point2 Warp::squareToStdNormal(const Point2 &sample) {
 }
 
 Float Warp::squareToStdNormalPdf(const Point2 &pos) {
-	return INV_TWOPI * std::exp(-(pos.x*pos.x + pos.y*pos.y)/2.0f);
+	return INV_TWOPI * math::fastexp(-(pos.x*pos.x + pos.y*pos.y)/2.0f);
 }
 
 static Float intervalToTent(Float sample) {

src/rfilters/gaussian.cpp

@@ -52,8 +52,8 @@ public:
 	Float eval(Float x) const {
 		Float alpha = -1.0f / (2.0f * m_stddev*m_stddev);
 		return std::max((Float) 0.0f,
-			std::exp(alpha * x * x) -
-			std::exp(alpha * m_radius * m_radius));
+			math::fastexp(alpha * x * x) -
+			math::fastexp(alpha * m_radius * m_radius));
 	}
 
 	std::string toString() const {