fix CUDA float4 issues

test/test_example.py

@@ -0,0 +1,24 @@
+import unittest
+from tinygrad.tensor import Tensor
+
+class TestExample(unittest.TestCase):
+  def test_example_readme(self):
+    x = Tensor.eye(3, requires_grad=True)
+    y = Tensor([[2.0,0,-2.0]], requires_grad=True)
+    z = y.matmul(x).sum()
+    z.backward()
+
+    print(x.grad.numpy())  # dz/dx
+    print(y.grad.numpy())  # dz/dy
+
+  def test_example_matmul(self):
+    x = Tensor.eye(256, requires_grad=True)
+    y = Tensor.eye(256, requires_grad=True)
+    z = y.matmul(x).sum()
+    z.backward()
+
+    print(x.grad.numpy())  # dz/dx
+    print(y.grad.numpy())  # dz/dy
+
+if __name__ == '__main__':
+  unittest.main()