feat(atenlib): op(trunc) (#515)

aten::trunc

```
<
  domain: "onnxscript.atenlib",
  opset_import: ["" : 18]
>
aten_trunc (self) => (return_val)
{
   tmp = Abs (self)
   integer_parts = Floor (tmp)
   tmp_0 = Constant <value = float tmp_0 {0}> ()
   tmp_0_cast = CastLike (tmp_0, self)
   is_negative = Less (self, tmp_0_cast)
   tmp_1 = Neg (integer_parts)
   return_val = Where (is_negative, tmp_1, integer_parts)
}
```

Author: justinchuby

onnxscript/function_libs/torch_aten/ops/core.py

@@ -5573,10 +5573,14 @@ def aten_true_divide(self: TensorType, other: TensorType) -> TensorType:
     raise NotImplementedError()
 
 
-def aten_trunc(self: TensorType) -> TensorType:
+@torch_op("aten::trunc")
+def aten_trunc(self: TFloatOrBFloat16) -> TFloatOrBFloat16:
     """trunc(Tensor self) -> Tensor"""
 
-    raise NotImplementedError()
+    # Reference https://github.com/onnx/onnx/issues/4588#issuecomment-1463970126
+    integer_parts = op.Floor(op.Abs(self))
+    is_negative = op.Less(self, 0.0)
+    return op.Where(is_negative, op.Neg(integer_parts), integer_parts)
 
 
 def aten_type_as(self: TensorType, other: TensorType) -> TensorType:

onnxscript/tests/function_libs/torch_aten/ops_correctness_test.py

@@ -389,6 +389,7 @@ def _where_input_wrangler(
     "tan": core_ops.aten_tan,
     "tanh": core_ops.aten_tanh,
     "topk": core_ops.aten_topk,
+    "trunc": core_ops.aten_trunc,
     "unsqueeze": core_ops.aten_unsqueeze,
     "view": core_ops.aten_view,
     "where": (core_ops.aten_where, _where_input_wrangler),