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Yes, Amit is right. The idBase should be 2^window and not
2^window-1. Infact, in the earliar code, it was 2^window
only. This way, for each pattern index in the feature types,
there is a 2^window (0 to (2^window-1)) feature ids reserved
at different offsets for each pattern index. If we keep it
2^(window-1), then feature ids will overlap as there is no
sufficient gap between two pattern's baseId.