Expose is_signed for dtype (#29511)

Summary:
Changelog:
- Expose is_signed for torch.dtype by modifying torch/csrc/Dtype.cpp
- Allow half, bfloat16 and bool to also been "known" by the isSignedType function
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29511

Test Plan:
- Add tests in test/test_torch.py

Closes https://github.com/pytorch/pytorch/issues/29475

Differential Revision: D18439030

Pulled By: albanD

fbshipit-source-id: 4b1f9da70c1c8dfd0a5bc028b6936acd1c64af47

c10/core/ScalarType.h

@@ -316,11 +316,11 @@ static inline bool isSignedType(ScalarType t) {
     case ScalarType::name:                       \
       return std::numeric_limits<ctype>::is_signed;
 
-    switch (t) {
-      AT_FORALL_SCALAR_TYPES_AND(Half, CASE_SIGNED)
-      default:
-        AT_ERROR("Unknown ScalarType");
-    }
+  switch (toUnderlying(t)) {
+    AT_FORALL_SCALAR_TYPES_AND3(Half, Bool, BFloat16, CASE_SIGNED)
+    default:
+      AT_ERROR("Unknown ScalarType");
+  }
   #undef CASE_SIGNED
 }
 

test/test_torch.py

@@ -2427,6 +2427,14 @@ class _TestTorchMixin(object):
         x = torch.Tensor([1, nan, 2])
         self.assertEqual(torch.isnan(x), torch.ByteTensor([0, 1, 0]))
 
+    def test_dtype_is_signed(self):
+        for dtype in torch.testing.get_all_dtypes():
+            self.assertEqual(dtype.is_signed, torch.is_signed(torch.tensor(0, dtype=dtype)))
+
+        self.assertFalse(torch.quint8.is_signed)
+        self.assertTrue(torch.qint8.is_signed)
+        self.assertTrue(torch.qint32.is_signed)
+
     def test_RNGState(self):
         state = torch.get_rng_state()
         stateCloned = state.clone()

torch/csrc/Dtype.cpp

@@ -29,6 +29,15 @@ PyObject *THPDtype_is_floating_point(THPDtype *self, PyObject *noargs)
   }
 }
 
+PyObject *THPDtype_is_signed(THPDtype *self, PyObject *noargs)
+{
+  if (at::isSignedType(self->scalar_type)) {
+    Py_RETURN_TRUE;
+  } else {
+    Py_RETURN_FALSE;
+  }
+}
+
 PyObject *THPDtype_reduce(THPDtype *self, PyObject *noargs)
 {
   /*
@@ -42,6 +51,7 @@ typedef PyObject *(*getter)(PyObject *, void *);
 
 static struct PyGetSetDef THPDtype_properties[] = {
   {"is_floating_point", (getter)THPDtype_is_floating_point, nullptr, nullptr, nullptr},
+  {"is_signed", (getter)THPDtype_is_signed, nullptr, nullptr, nullptr},
   {nullptr}
 };