message: Optimize Mish for CPU backend
diff: @@ -667,8 +667,11 @@ struct MishFunctor : public BaseFunctor
  {
  for( int i = 0; i < len; i++ )
  {
  + // Use fast approximation introduced in https://github.com/opencv/opencv/pull/17200
  float x = srcptr[i];
  - dstptr[i] = x * tanh(log(1.0f + exp(x)));
  + float eX = exp(std::min(x, 20.f));
  + float n = (eX + 2) * eX;
  + dstptr[i] = (x * n) / (n + 2);
  }
  }
  }
  