Decoding device and coding method

A coding method implemented by a processing unit of a computing device, comprising:

• encoding stages in which one of N code streams is generated by encoding multiple unit symbols each having an N×M bit width (N, M both are positive integers) in such a way that i (1<=i<=N) partial symbol from a top symbol of unit symbols pertains to the i code stream;
• wherein
• the step of encoding is performed by the processing unit;
• at the time of encoding one partial symbol, in which a hierarchical structure of N-level hierarchy which connects multiple probabilistic models and each hierarchy of the relevant hierarchical structure corresponds one-to-one to each of the N code streams;
• one of the stages is a specific stage which specifies one of the multiple probabilistic models on the basis of the hierarchical structure connected in such a way that probabilistic models which pertain to a leaf side of the relevant hierarchical structure is specified on the basis of the value of the other corresponding partial symbol which pertain to a unit symbol which is similar to one partial symbol encoded using probabilistic models pertaining to the lateral side hierarchy and probabilistic models pertaining to the relevant lateral side;
• and
• the step of encoding includes a separate encoding step in which the previous partial symbol is encoded using previously specified probabilistic models.