Reaction of glucose with hydrogen iodide and heat?? (plz read below)

The reaction of glucose with hydrogen iodide and then heating gives hexane according to my text.
But i dont understand. plz explain
alcohol reacts with HI to form alkylhalide and if we heat it iodine will be eliminated producing alkene so how is hexane formed. Also how i carbonyl group reduced with HI

Alkyl iodides can react with HI to undergo reverse halogenation.
RI + HI ---> RH + I2