Interval width update process in the arithmetic coding method

摘要

The present invention relates to an interval width update process in arithmetic coding, characterized in thatPPa set of values ={A[0],A[1], . . . ,A[r-1]}, is selected and the interval width is maintained as an index Wi in said set,PPa single table lookup simultaneously updates the interval width and supplies the augend and shift by performing the following operation:PP (Wi+1, Xi, Ri)=ƒ"(Si, Wi)PP in which the function . function." is implemented by a single table lookup, in which p(Si) and P(Si) are determined from Si, A[Wi] is determined from Wi, p(Si)· A[Wi] and Ri=P(Si)·A[Wi] are computed, the shift Xi necessary for representing p(Si)·A[Wi]·2.sup.Xi in is determined. Wi+1 is determined in such a way that A[Wi+1] is the best representative of p(Si) ·A[Wi]·2.sup.Xi, followed by return to Wi+1, Xi and Ri.