Merge lp:~habnabit/pyskein/getrandbits into lp:pyskein

[Aaron Gallagher]

Submitting a branch for fixing #1198768.

Unmerged revisions

419. By Aaron Gallagher on 2013-07-08

Add skein.Random.getrandbits and a test.

=== modified file 'src/skein.py'
--- src/skein.py	2011-06-04 14:14:40 +0000
+++ src/skein.py	2013-07-08 01:35:29 +0000
@@ -98,6 +98,15 @@
         return r * self._RECIP_BPF
 
 
+    def getrandbits(self, n_bits):
+        """Get some number of random bits as an integer."""
+        if n_bits <= 0:
+            raise ValueError('number of bits must be greater than zero')
+        n_bytes = (n_bits + 7) // 8
+        val = int.from_bytes(self.read(n_bytes), 'little')
+        return val >> (n_bytes * 8 - n_bits)
+
+
     def getstate(self):
         """Return internal state; can be passed to setstate() later."""
         return (self._state,
 
=== modified file 'test/test_skein.py'
--- test/test_skein.py	2010-12-22 16:49:46 +0000
+++ test/test_skein.py	2013-07-08 01:35:29 +0000
@@ -202,6 +202,14 @@
             self.assertEqual(r.read(i)+r.read(5000-i),
                              skein.Random(b"abc").read(5000))
 
+    def testPRNGgetrandbitsAdvancesState(self):
+        r1 = skein.Random(b"123", hasher=self.HASHER)
+        s1 = r1.read(2)
+        r1.getrandbits(32)
+        s2 = r1.read(2)
+        r2 = skein.Random(b"123", hasher=self.HASHER)
+        self.assertNotEqual(s1 + s2, r2.read(4))
+
     def testStreamCipher(self):
         c = skein.StreamCipher(key=b"secret", hasher=self.HASHER)
         x = c.encrypt(b"foobar")