Arithmetic encoder for arithmetically encoding and arithmetic decoder for arithmetically decoding a sequence of information values, methods for arithmetically encoding and decoding a sequence of information values and computer program for implementing these methods

A method of arithmetically encoding a sequence of information values into a bitstream, the bitstream comprising an arithmetic coded bitstream, the method comprising:

• symbolizing the information values into symbol strings so as to acquire a sequence of symbols;
• arithmetically encoding the sequence of symbols by
• subdividing a current interval, which defines a current version of a coding state of an arithmetic encoder, for each symbol, according to a probability estimate for a respective symbol, into a plurality of subintervals,
• selecting a subinterval out of the plurality of the subintervals according to a symbol value of the respective symbol so as to acquire an updated version of the coding state of the arithmetic encoder, defined by the selected subinterval, for encoding a next symbol of the sequence of symbols,
• renormalizing encoder-internal parameters which define the coding state under continuing the bitstream, and
• providing the bitstream with entry point information allowing for resuming arithmetic decoding the bitstream from a predetermined entry point onward,
• wherein the entry point information comprises information on a coding state of an arithmetic decoder, which occurs in the arithmetic decoder when the arithmetic decoder decodes the bitstream until the predetermined entry point,
• wherein the coding state of the arithmetic decoder is defined by decoder-internal parameters comprising an interval width parameter indicating a width of the current interval and a pointer pointing into the current interval and the information on the coding state of the arithmetic decoder comprises a value of the pointer while being free of a value of the interval width parameter, the method further comprising
• setting the value of the interval width parameter comprised by the information on the coding state of the arithmetic decoder to be equal to a predetermined value and using the predetermined value for the interval width parameter when resuming the arithmetic encoding the sequence of symbols from the predetermined entry point onwards, or
• preliminarily interrupting the arithmetic encoding the sequence of symbols by arithmetically encoding a symbol of a predetermined symbol value immediately ahead the predetermined entry point before resuming the arithmetic encoding the sequence of symbols from the predetermined entry point onwards, and set the value of the interval width parameter comprised by the information on the coding state of the arithmetic decoder to be equal to a current value of the interval width parameter as manifesting itself in the arithmetic encoding the sequence of symbols up to the predetermined entry point, comprising the symbol of the predetermined symbol value.