Issue with mpreal and std::numeric_limits, i.e. digits is not a constant. Added a digits() traits in NumTraits with fallback to static constant. Specialization for mpreal added in MPRealSupport.

1 files changed, 34 insertions, 0 deletions

diff --git a/Eigen/src/Core/NumTraits.h b/Eigen/src/Core/NumTraits.h
index aebc0c259..4d896a098 100644
--- a/Eigen/src/Core/NumTraits.h
+++ b/Eigen/src/Core/NumTraits.h
@@ -41,6 +41,34 @@ struct default_digits10_impl<T,false,true> // Integer
   static int run() { return 0; }
 };
 
+
+// default implementation of digits(), based on numeric_limits if specialized,
+// 0 for integer types, and log2(epsilon()) otherwise.
+template< typename T,
+          bool use_numeric_limits = std::numeric_limits<T>::is_specialized,
+          bool is_integer = NumTraits<T>::IsInteger>
+struct default_digits_impl
+{
+  static int run() { return std::numeric_limits<T>::digits; }
+};
+
+template<typename T>
+struct default_digits_impl<T,false,false> // Floating point
+{
+  static int run() {
+    using std::log;
+    using std::ceil;
+    typedef typename NumTraits<T>::Real Real;
+    return int(ceil(-log(NumTraits<Real>::epsilon())/log(static_cast<Real>(2))));
+  }
+};
+
+template<typename T>
+struct default_digits_impl<T,false,true> // Integer
+{
+  static int run() { return 0; }
+};
+
 } // end namespace internal
 
 /** \class NumTraits
@@ -119,6 +147,12 @@ template<typename T> struct GenericNumTraits
   }
 
   EIGEN_DEVICE_FUNC
+  static inline int digits()
+  {
+    return internal::default_digits_impl<T>::run();
+  }
+
+  EIGEN_DEVICE_FUNC
   static inline Real dummy_precision()
   {
     // make sure to override this for floating-point types