The present invention provides a backlight module, comprising a light source module and an optical control layer disposed on the light source module. Said method comprises a step of the statistical analysis of driving vectors representing the signal determining a finished set of code vectors representing said driving vectors. An additional string entry is added to the data structure based on a combination of the current portion and a previous portion of the input stream, wherein the additional string entry corresponds to a subset of the combination that fails to match any of the plurality of existing string entries in the data structure.