Use a pure-python version of bisect_left, to fix 32-bit issues

The default bisect module includes a fast C implementation, which
requires that array indices fit within the system "long" type.  For
32-bit systems, that's not acceptable, as the table indices for raw
data can exceed 2^32 very quickly.  A pure python version works fine.

nilmdb/server/nilmdb.py

@@ -23,7 +23,6 @@ from nilmdb.server.errors import NilmDBError, StreamError, OverlapError
 import sqlite3
 import os
 import errno
-import bisect
 
 # Note about performance and transactions:
 #
@@ -516,6 +515,17 @@ class NilmDB(object):
         # And that's all
         return
 
+    def _bisect_left(self, a, x, lo, hi):
+        # Like bisect.bisect_left, but doesn't choke on large indices on
+        # 32-bit systems, like bisect's fast C implementation does.
+        while lo < hi:
+            mid = (lo + hi) / 2
+            if a[mid] < x:
+                lo = mid + 1
+            else:
+                hi = mid
+        return lo
+
     def _find_start(self, table, dbinterval):
         """
         Given a DBInterval, find the row in the database that
@@ -526,10 +536,10 @@ class NilmDB(object):
         # Optimization for the common case where an interval wasn't truncated
         if dbinterval.start == dbinterval.db_start:
             return dbinterval.db_startpos
-        return bisect.bisect_left(table,
+        return self._bisect_left(table,
-                                  dbinterval.start,
+                                 dbinterval.start,
-                                  dbinterval.db_startpos,
+                                 dbinterval.db_startpos,
-                                  dbinterval.db_endpos)
+                                 dbinterval.db_endpos)
 
     def _find_end(self, table, dbinterval):
         """
@@ -545,10 +555,10 @@ class NilmDB(object):
         # want to include the given timestamp in the results.  This is
         # so a queries like 1:00 -> 2:00 and 2:00 -> 3:00 return
         # non-overlapping data.
-        return bisect.bisect_left(table,
+        return self._bisect_left(table,
-                                  dbinterval.end,
+                                 dbinterval.end,
-                                  dbinterval.db_startpos,
+                                 dbinterval.db_startpos,
-                                  dbinterval.db_endpos)
+                                 dbinterval.db_endpos)
 
     def stream_extract(self, path, start = None, end = None,
                        count = False, markup = False, binary = False):