Move some utility functions into the cdsl package.

- is_power_of_two
- next_power_of_two

Make sure we run doctests on these functions.

lib/cretonne/meta/constant_hash.py

@@ -6,6 +6,7 @@ don't attempt parfect hashing, but simply generate an open addressed
 quadratically probed hash table.
 """
 from __future__ import absolute_import
+from cdsl import next_power_of_two
 
 
 def simple_hash(s):
@@ -24,27 +25,6 @@ def simple_hash(s):
     return h
 
 
-def next_power_of_two(x):
-    """
-    Compute the next power of two that is greater than `x`:
-        >>> next_power_of_two(0)
-        1
-        >>> next_power_of_two(1)
-        2
-        >>> next_power_of_two(2)
-        4
-        >>> next_power_of_two(3)
-        4
-        >>> next_power_of_two(4)
-        8
-    """
-    s = 1
-    while x & (x + 1) != 0:
-        x |= x >> s
-        s *= 2
-    return x + 1
-
-
 def compute_quadratic(items, hash_function):
     """
     Compute an open addressed, quadratically probed hash table containing