Profiling speedup #3: reduce number of function calls inside get_index_from_base_index because it gets called *a lot* in loops

atrcopy/segments.py

@@ -606,7 +606,7 @@ class DefaultSegment(object):
             index = r.get_reverse_index(base_index)
         else:
             index = base_index - r.get_raw_index(0)
-            if not self.is_valid_index(index):
+            if index < 0 or index >= self.rawdata.data_length:
                 raise IndexError("index %d not in this segment" % base_index)
         return index