AN APPARATUS, METHOD, AND PROGRAMS FOR ARITHMETIC ENCODING AND DECODING

The present invention aims to increase an encoding efficiency when the occurrence probability of LPS (less probable symbol) is low. An encoding apparatus has a interval size (A), a interval limit value (C), divides a set interval which is set on a number line, selects a sub-interval corresponding to an occurring symbol, updates the interval size (A) and the interval limit value (C) with a limited precision based on the selected sub-interval size, and encodes a coordinate within the interval. Based on the probability (the occurrence probability of symbol) output from a learning memory, the sub-interval size (LSZ, dLSZ) and the sub-interval limit value are obtained. A correction value calculator computes the correction value based on the dLSZ, reflects the computed correction value (dA, dC) to the renormalized subinterval size (rA) and the renormalized sub-interval limit value (rC), updates the interval size (A7) to the sub-interval size, updates the interval limit value (C8) to the sub-interval limit value, and outputs a code.