From b97911dd189c0377df6ba4ef1a710105b9437a3c Mon Sep 17 00:00:00 2001
From: Till Hoffmann <tillahoffmann@gmail.com>
Date: Mon, 4 Apr 2016 19:16:03 +0100
Subject: Refactored code into type-specific helper functions.

---
 Eigen/src/Core/SpecialFunctions.h | 86 +++++++++++++++++++++++++++++----------
 1 file changed, 65 insertions(+), 21 deletions(-)

(limited to 'Eigen/src/Core/SpecialFunctions.h')

diff --git a/Eigen/src/Core/SpecialFunctions.h b/Eigen/src/Core/SpecialFunctions.h
index 26b92607c..772449bc7 100644
--- a/Eigen/src/Core/SpecialFunctions.h
+++ b/Eigen/src/Core/SpecialFunctions.h
@@ -744,6 +744,56 @@ struct zeta_impl {
 };
     
 #else
+
+template <typename Scalar>
+struct zeta_impl_series {
+  EIGEN_DEVICE_FUNC
+  static EIGEN_STRONG_INLINE Scalar run(const Scalar) {
+    EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false),
+                        THIS_TYPE_IS_NOT_SUPPORTED);
+    return Scalar(0);
+  }
+};
+
+template <>
+struct zeta_impl_series<float> {
+  EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
+  static bool run(float& a, float& b, float& s, const float x, const float machep) {
+    int i = 0;  
+    while(i < 9)
+    {
+        i += 1;
+        a += 1.0f;
+        b = numext::pow( a, -x );
+        s += b;
+        if( numext::abs(b/s) < machep )
+            return true;
+    }
+    
+    //Return whether we are done
+    return false;
+  }
+};
+
+template <>
+struct zeta_impl_series<double> {
+  EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
+  static bool run(double& a, double& b, double& s, const double x, const double machep) {
+    int i = 0;  
+    while( (i < 9) || (a <= 9.0) )
+    {
+        i += 1;
+        a += 1.0;
+        b = numext::pow( a, -x );
+        s += b;
+        if( numext::abs(b/s) < machep )
+            return true;
+    }
+    
+    //Return whether we are done
+    return false;
+  }
+};
     
 template <typename Scalar>
 struct zeta_impl {
@@ -809,18 +859,18 @@ struct zeta_impl {
         Scalar p, r, a, b, k, s, t, w;
         
         const Scalar A[] = {
-            12.0,
-            -720.0,
-            30240.0,
-            -1209600.0,
-            47900160.0,
-            -1.8924375803183791606e9, /*1.307674368e12/691*/
-            7.47242496e10,
-            -2.950130727918164224e12, /*1.067062284288e16/3617*/
-            1.1646782814350067249e14, /*5.109094217170944e18/43867*/
-            -4.5979787224074726105e15, /*8.028576626982912e20/174611*/
-            1.8152105401943546773e17, /*1.5511210043330985984e23/854513*/
-            -7.1661652561756670113e18 /*1.6938241367317436694528e27/236364091*/
+            Scalar(12.0),
+            Scalar(-720.0),
+            Scalar(30240.0),
+            Scalar(-1209600.0),
+            Scalar(47900160.0),
+            Scalar(-1.8924375803183791606e9), /*1.307674368e12/691*/
+            Scalar(7.47242496e10),
+            Scalar(-2.950130727918164224e12), /*1.067062284288e16/3617*/
+            Scalar(1.1646782814350067249e14), /*5.109094217170944e18/43867*/
+            Scalar(-4.5979787224074726105e15), /*8.028576626982912e20/174611*/
+            Scalar(1.8152105401943546773e17), /*1.5511210043330985984e23/854513*/
+            Scalar(-7.1661652561756670113e18) /*1.6938241367317436694528e27/236364091*/
             };
             
         const Scalar maxnum = NumTraits<Scalar>::infinity();
@@ -854,16 +904,10 @@ struct zeta_impl {
          */
         s = numext::pow( q, -x );
         a = q;
-        i = 0;
         b = zero;
-        while( (i < 9) || (a <= Scalar(9)) )
-        {
-            i += 1;
-            a += one;
-            b = numext::pow( a, -x );
-            s += b;
-            if( numext::abs(b/s) < machep )
-                return s;
+        // Run the summation in a helper function that is specific to the floating precision
+        if (zeta_impl_series<Scalar>::run(a, b, s, x, machep)) {
+            return s;
         }
         
         w = a;
-- 
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