exportable Hardswish() implementation

utils/activations.py

@@ -10,6 +10,13 @@ class Swish(nn.Module):  #
         return x * torch.sigmoid(x)
 
 
+class Hardswish(nn.Module):  # alternative to nn.Hardswish() for export
+    @staticmethod
+    def forward(x):
+        # return x * F.hardsigmoid(x)
+        return x * F.hardtanh(x + 3, 0., 6.) / 6.
+
+
 class MemoryEfficientSwish(nn.Module):
     class F(torch.autograd.Function):
         @staticmethod