Merge pull request opencv#17916 from SinM9:mish_functor_sin

Author: alalek

modules/dnn/src/layers/elementwise_layers.cpp

@@ -669,9 +669,14 @@ struct MishFunctor : public BaseFunctor
             {
                 // Use fast approximation introduced in https://github.com/opencv/opencv/pull/17200
                 float x = srcptr[i];
-                float eX = exp(std::min(x, 20.f));
-                float n = (eX + 2) * eX;
-                dstptr[i] = (x * n) / (n + 2);
+                if (x >= 8.f)
+                    dstptr[i] = x;
+                else
+                {
+                    float eX = exp(x);
+                    float n = (eX + 2) * eX;
+                    dstptr[i] = (x * n) / (n + 2);
+                }
             }
         }
     }