Binary Arithmetic Decoder and Binary Arithmetic Decoding Device

A binary arithmetic decoder comprising:

• a binary-arithmetic-decoding processing unit that decodes input encoded data into binary data and outputs the binary data;
• a multi-value unit that converts the binary data output by the binary-arithmetic-decoding processing unit into multi-value data and outputs the multi-value data;
• and
• a context-index calculating unit that derives a context index based on the decoded binary data and the multi-value data and outputs the context index to the binary-arithmetic-decoding processing unit, wherein
• the binary-arithmetic-decoding processing unit includes:
• a context-variable retaining unit that derives, based on the context index output from the context-index calculating unit, a first context variable included a first probability state index representing a code occurrence probability and a value of a first superior probability code having a high occurrence probability and retains the first context variable;
• a range-length/offset-variable retaining unit that retains a range length indicating an entire section length in a real number section of an occurrence probability and an offset indicating a present position in the range length;
• a first LPS/MPS determining unit that determines, using the first probability state index, the range length, and the offset, whether a code of first binary data is an inferior probability code or a superior probability code and outputs a result of the determination;
• a first renormalization processing unit that performs renormalization processing on the range length and the offset;
• and
• a context-variable calculating unit that derives the first binary data using the first context variable and the determination result and outputs the first binary data to the multi-value unit, and
• the first renormalization processing unit:
• in parallel to determination processing of the first LPS/MPS determining unit, regards the code of the first binary data as the inferior probability code, updates the range length and the offset, and performs first renormalization processing on the range length and the offset after the update until the range length after the update becomes a predetermined section length or more,
• in parallel to the determination processing of the first LPS/MPS determining unit, regards the code of the first binary data as the superior probability code, updates the range length and the offset, and performs second renormalization processing on the range length and the offset after the update until the range length after the update becomes a predetermined section length or more, and
• selects, according to the determination result, the range length and the offset after renormalization by the first renormalization processing or the range length and the offset after renormalization by the second renormalization processing and outputs the range length and the offset to the range-length/offset-variable retaining unit.