Some minor changes to avoid compiler errors in cygwin.

dlib/float_details.h

@@ -105,11 +105,18 @@ namespace dlib
 
         double      _frexp(double      v, int* e) const { return frexp(v,e); }
         float       _frexp(float       v, int* e) const { return frexpf(v,e); }
-        long double _frexp(long double v, int* e) const { return frexpl(v,e); }
 
         double      _ldexp(double      v, int e) const { return ldexp(v,e); }
         float       _ldexp(float       v, int e) const { return ldexpf(v,e); }
+
+#ifdef __CYGWIN__
+        // frexpl and ldexpl aren't available on cygwin so just use the double version.
+        long double _frexp(long double v, int* e) const { return _frexp((double)v,e); }
+        long double _ldexp(long double v, int e) const { return _ldexp((double)v,e); }
+#else
+        long double _frexp(long double v, int* e) const { return frexpl(v,e); }
         long double _ldexp(long double v, int e) const { return ldexpl(v,e); }
+#endif
 
         template <typename T>
         void convert_from_T (

dlib/statistics/vector_normalizer_frobmetric.h

@@ -157,7 +157,7 @@ namespace dlib
                 unsigned long max_iter_
             ) 
             {
-                _C = C_;
+                _c = C_;
 
                 _cur_iter = 0;
                 _gradient_thresh = eps_;
@@ -178,7 +178,7 @@ namespace dlib
                 for (long i = 0; i < grad.size(); ++i)
                 {
                     const bool at_lower_bound = (0 >= u(i) && grad(i) > 0);
-                    const bool at_upper_bound = (_C/grad.size() <= u(i) && grad(i) < 0);
+                    const bool at_upper_bound = (_c/grad.size() <= u(i) && grad(i) < 0);
                     if (!at_lower_bound && !at_upper_bound)
                         max_gradient = std::max(std::abs(grad(i)), max_gradient);
                 }
@@ -207,7 +207,7 @@ namespace dlib
 
             unsigned long _max_iter;
             unsigned long _cur_iter;
-            double _C;
+            double _c;
             double _gradient_thresh;
         };