refactor 2

Author: sivasathyaseeelan

src/PoissonRandom.jl

@@ -84,29 +84,30 @@ end
 
 # Procedure F
 function procf(λ, K::Int, s::Float64)
-    INV_SQRT_2PI = 0.3989422804014327  # 1/sqrt(2π)
+    # can be pre-computed, but does not seem to affect performance
+    INV_SQRT_2PI = inv(sqrt(2pi))
     ω = INV_SQRT_2PI / s
-    b1 = 1 / (24 * λ)
-    b2 = 0.3 * b1^2
-    c3 = b1 * b2 / 7
+    b1 = inv(24) / λ
+    b2 = 0.3 * b1 * b1
+    c3 = inv(7) * b1 * b2
     c2 = b2 - 15 * c3
     c1 = b1 - 6 * b2 + 45 * c3
     c0 = 1 - b1 + 3 * b2 - 15 * c3
 
     if K < 10
         px = -λ
-        log_py = K * log(λ) - loggamma(K + 1)  # log(K!) via loggamma
+        log_py = K * log(λ) - loggamma(K + 1) # log(K!) via loggamma
         py = exp(log_py)
     else
-        δ = 1 / (12 * K)
+        δ = inv(12) / K
         δ -= 4.8 * δ^3
         V = (λ - K) / K
-        px = K * log1pmx(V) - δ  # avoids need for table
+        px = K * log1pmx(V) - δ # avoids need for table
         py = INV_SQRT_2PI / sqrt(K)
     end
     X = (K - λ + 0.5) / s
     X2 = X^2
-    fx = -X2 / 2 # missing negation in pseudo-algorithm, but appears in fortran code.
+    fx = X2 / -2 # missing negation in pseudo-algorithm, but appears in fortran code.
     fy = ω * (((c3 * X2 + c2) * X2 + c1) * X2 + c0)
     return px, py, fx, fy
 end