Update optimized Delta codec for bool (#595)

* Update optimized `Delta` codec for `bool`

Previously `bool` just worked with `Delta`. However this was not
actually tested. The optimized version switched to `np.subtract` for
in-place computation, which works for other types. Though `bool` needs
special handling. Fortunately this can be done with `np.not_equal`,
which has the same behavior.

Also include a test for `bool` data to make sure this is handled
correctly going forward.

* Simplify type check

This is a bit more succinct and gets to the core point. Namely
`arr.dtype` determines this code path.

Also comparing directly to `bool` works here. It is a bit faster as well
since we need not construct an `np.dtype` object.

* Drop extraneous `0`s

numcodecs/delta.py

@@ -64,7 +64,10 @@ def encode(self, buf):
 
         # compute differences
         # using np.subtract for in-place operations
-        np.subtract(arr[1:], arr[0:-1], out=enc[1:])
+        if arr.dtype == bool:
+            np.not_equal(arr[1:], arr[:-1], out=enc[1:])
+        else:
+            np.subtract(arr[1:], arr[:-1], out=enc[1:])
 
         return enc
 

numcodecs/tests/test_delta.py

@@ -14,6 +14,7 @@
 # mix of shapes: 1D, 2D, 3D
 # mix of orders: C, F
 arrays = [
+    np.random.randint(0, 1, size=110, dtype='?').reshape(10, 11),
     np.arange(1000, dtype='<i4'),
     np.linspace(1000, 1001, 1000, dtype='<f4').reshape(100, 10),
     np.random.normal(loc=1000, scale=1, size=(10, 10, 10)).astype('<f8'),