Specify correct uuid variant in convert_time_to_uuid

Related to pycassa#180

pycassa/util.py

@@ -84,29 +84,30 @@ def convert_time_to_uuid(time_arg, lowest_val=True, randomize=False):
 
     if randomize:
         rand_bits = random.getrandbits(8 + 8 + 48)
-        clock_seq_low = rand_bits & 0xffL # 8 bits, no offset
-        clock_seq_hi_variant = (rand_bits & 0xff00L) / 0x100 # 8 bits, 8 offset
-        node = (rand_bits & 0xffffffffffff0000L) / 0x10000L # 48 bits, 16 offset
+        clock_seq_low = rand_bits & 0xffL  # 8 bits, no offset
+        # keep the first two bits as 10 for the uuid variant
+        clock_seq_hi_variant = 0b10000000 | (0b00111111 & ((rand_bits & 0xff00L) >> 8))  # 8 bits, 8 offset
+        node = (rand_bits & 0xffffffffffff0000L) >> 16  # 48 bits, 16 offset
     else:
         # In the event of a timestamp tie, Cassandra compares the two
         # byte arrays directly. This is a *signed* comparison of each byte
         # in the two arrays.  So, we have to make each byte -128 or +127 for
         # this to work correctly.
         #
         # For the clock_seq_hi_variant, we don't get to pick the two most
-        # significant bits (they're always 01), so we are dealing with a
+        # significant bits (they're always 10), so we are dealing with a
         # positive byte range for this particular byte.
         if lowest_val:
             # Make the lowest value UUID with the same timestamp
             clock_seq_low = 0x80L
-            clock_seq_hi_variant = 0 & 0x3fL # The two most significant bits
-                                             # will be 0 and 1, no matter what
+            clock_seq_hi_variant = 0 & 0x80L # The two most significant bits
+                                             # will be 10 for the variant
             node = 0x808080808080L # 48 bits
         else:
             # Make the highest value UUID with the same timestamp
             clock_seq_low = 0x7fL
-            clock_seq_hi_variant = 0x3fL # The two most significant bits will
-                                         # 0 and 1, no matter what
+            clock_seq_hi_variant = 0xbfL # The two most significant bits will
+                                         # 10 for the variant
             node = 0x7f7f7f7f7f7fL # 48 bits
     return uuid.UUID(fields=(time_low, time_mid, time_hi_version,
                         clock_seq_hi_variant, clock_seq_low, node), version=1)