Added U64 which always returns a long.

Added some comments.

src/ZODB/utils.py

@@ -88,6 +88,7 @@ import TimeStamp, time, struct
 t32 = 1L << 32
 
 def p64(v, pack=struct.pack):
+    """Pack an integer or long into a 8-byte string"""
     if v < t32: h=0
     else:
         h=v/t32
@@ -95,6 +96,7 @@ def p64(v, pack=struct.pack):
     return pack(">II", h, v)
 
 def u64(v, unpack=struct.unpack):
+    """Unpack an 8-byte string into a 64-bit (or long) integer"""
     h, v = unpack(">ii", v)
     if v < 0: v=t32+v
     if h:
@@ -102,6 +104,13 @@ def u64(v, unpack=struct.unpack):
         v=h*t32+v
     return v
 
+def U64(v, unpack=struct.unpack):
+    """Same as u64 but always returns a long."""
+    h, v = unpack(">II", v)
+    if h:
+        v=h*t32+v
+    return v
+
 def cp(f1, f2, l):
     read=f1.read
     write=f2.write