1. A decoder of Low Density Parity Check codewords on GF(r q ), the decoder using the iterative belief propagation algorithm and comprising at least storing means to store a posteriori information on variables; updating means to update the a posteriori information on variables; first computation means to compute variable to constraint messages from a posteriori information on variables and variable to constraint messages from previous iteration; second computation means to compute constraint to variable messages from variable to constraint messages computed by the first computation means; and third and fourth computation means to update the a posteriori information on variables; wherein the decoder comprises: first shuffle means to transfer the a posteriori information on variables to the first computation means; second shuffle means to transfer information from the third computation means to the fourth computation means; and compression-storage-decompression means of constraint to variable messages.