Switch to mathutil from pyutil (it has tests, and has already been ported to

Python 3).

src/allmydata/util/_python3.py

@@ -17,6 +17,7 @@ if PY2:
 PORTED_MODULES = [
     "allmydata.util.assertutil",
     "allmydata.util.humanreadable",
+    "allmydata.util.mathutil",
     "allmydata.util.namespace",
     "allmydata.util._python3",
 ]

src/allmydata/util/mathutil.py

@@ -1,71 +1,20 @@
 """
 A few commonly needed functions.
+
+Backwards compatibility for direct imports.
+
+Ported to Python 3.
 """
 
-import math
+from __future__ import division
+from __future__ import absolute_import
+from __future__ import print_function
+from __future__ import unicode_literals
 
-def div_ceil(n, d):
-    """
-    The smallest integer k such that k*d >= n.
-    """
-    return (n/d) + (n%d != 0)
+from future.utils import PY2
+if PY2:
+    from builtins import filter, map, zip, ascii, chr, hex, input, next, oct, open, pow, round, super, bytes, dict, int, list, object, range, str, max, min  # noqa: F401
 
-def next_multiple(n, k):
-    """
-    The smallest multiple of k which is >= n.
-    """
-    return div_ceil(n, k) * k
 
-def pad_size(n, k):
-    """
-    The smallest number that has to be added to n so that n is a multiple of k.
-    """
-    if n%k:
-        return k - n%k
-    else:
-        return 0
-
-def is_power_of_k(n, k):
-    return k**int(math.log(n, k) + 0.5) == n
-
-def next_power_of_k(n, k):
-    if n == 0:
-        x = 0
-    else:
-        x = int(math.log(n, k) + 0.5)
-    if k**x < n:
-        return k**(x+1)
-    else:
-        return k**x
-
-def ave(l):
-    return sum(l) / len(l)
-
-def log_ceil(n, b):
-    """
-    The smallest integer k such that b^k >= n.
-
-    log_ceil(n, 2) is the number of bits needed to store any of n values, e.g.
-    the number of bits needed to store any of 128 possible values is 7.
-    """
-    p = 1
-    k = 0
-    while p < n:
-        p *= b
-        k += 1
-    return k
-
-def log_floor(n, b):
-    """
-    The largest integer k such that b^k <= n.
-    """
-    p = 1
-    k = 0
-    while p <= n:
-        p *= b
-        k += 1
-    return k - 1
-
-def round_sigfigs(f, n):
-    fmt = "%." + str(n-1) + "e"
-    return float(fmt % f)
+# The API importers expect:
+from pyutil.mathutil import div_ceil, next_multiple, pad_size, is_power_of_k, next_power_of_k, ave, log_ceil, log_floor, round_sigfigs