fix div 0 error of fftfreq (#49954)

* fix div 0 error of fftfreq

* fix div 0 error of fftfreq

* bug fix

* add 'n' value check

python/paddle/fft.py

@@ -1275,6 +1275,8 @@ def fftfreq(n, d=1.0, dtype=None, name=None):
             #  Tensor(shape=[5], dtype=float32, place=CUDAPlace(0), stop_gradient=True,
             #           [ 0.        ,  0.40000001,  0.80000001, -0.80000001, -0.40000001])
     """
+    if d * n == 0:
+        raise ValueError("d or n should not be 0.")
 
     dtype = paddle.framework.get_default_dtype()
     val = 1.0 / (n * d)

python/paddle/fluid/tests/unittests/fft/test_fft.py

@@ -1823,6 +1823,23 @@ class TestFftFreq(unittest.TestCase):
             )
 
 
+@place(DEVICES)
+@parameterize(
+    (TEST_CASE_NAME, 'n', 'd', 'dtype', 'expect_exception'),
+    [
+        ('test_with_0_0', 0, 0, 'float32', ValueError),
+        ('test_with_n_0', 20, 0, 'float32', ValueError),
+        ('test_with_0_d', 0, 20, 'float32', ValueError),
+    ],
+)
+class TestFftFreqException(unittest.TestCase):
+    def test_fftfreq2(self):
+        """Test fftfreq with d = 0"""
+        with paddle.fluid.dygraph.guard(self.place):
+            with self.assertRaises(self.expect_exception):
+                paddle.fft.fftfreq(self.n, self.d, self.dtype)
+
+
 @place(DEVICES)
 @parameterize(
     (TEST_CASE_NAME, 'n', 'd', 'dtype'),