Arithmetic encoding and decoding of an information signal

A method comprising the steps of:

• providing a sequence of n-bit symbols, n being an integer and n.gtoreq.1;
• providing finite sized first and second registers for storing an A parameter and a C parameter, respectively, the C parameter having a relationship with a boundary of a value interval and the A parameter having a relationship with the size of the interval;
• (a) inputting a symbol of the information signal and a value of at least one corresponding probability of the symbol for encoding;
• (b) retrieving the values for the A and C parameters from the first and second registers, respectively, truncating the value of the A parameter 0.b.sub.0 b.sub.1 . . . b.sub.i-1 b.sub.i . . . to bit b.sub.i-1, and if b.sub.i-1 =`0` and b.sub.i =`1` then raising b.sub.i-1 to `1`;
• (c) splitting the value interval corresponding to the value retrieved from the first register into sub intervals corresponding to the at least one probability value, and selecting one of the subintervals in response to the symbol;
• (d) updating the value of at least the A parameter to correspond with the size of the selected subinterval, in order to become the new size of the interval for encoding the next symbol in the information signal;
• (e) storing the updated value for the A parameter in the first register;
• (f) continuing the method starting at step (a) for encoding the next symbol.

A method comprising the steps of:

• providing a sequence of n-bit symbols, n being an integer and n.gtoreq.1;
• providing finite sized first and second registers for storing an A parameter and a C parameter, respectively, the C parameter having a relationship with a boundary of a value interval and the A parameter having a relationship with the size of the interval;
• (a) inputting a symbol of the information signal and at least one corresponding probability value of the associated symbol for encodings;
• (b) retrieving the values for the A and C parameters from the first and second registers, respectively, truncating the value of the A parameter 0.b.sub.0 b.sub.1 . . . b.sub.i-1 b.sub.i . . . to bit b.sub.i-1, and making bit b.sub.i-1 equal to `1`;
• (c) splitting the value interval corresponding to the value retrieved from the first register into sub intervals corresponding to the at least one probability value, and selecting one of the subintervals in response to the symbol;
• (d) updating the value of at least the A parameter to correspond with the size of the selected subinterval, in order to become the new size of the interval for encoding the next symbol in the information signal;
• (e) storing the updated value for the A parameter in the first registers;
• (f) continuing the method starting at step (a) for encoding the next symbol.

Apparatus comprising:

• input means for receiving an arithmetically encoded information signal;
• finite sized first and second registers, the first register for storing an A parameter, the A parameter having a relationship with a size of a value interval, the second register for storing a C parameter, the contents of the second register before a decoding step being obtained from the contents of the second register obtained in a previous decoding step, by shifting m bits of the arithmetically encoded information signal into the second register, where m is a variable integer and m.gtoreq.0;
• generator means for generating at least one probability value for an associated symbol to be decoded;
• retrieval means for retrieving the values for the A and C parameters from the first and second registers, respectively, including means if b.sub.i equals `1`, for truncating the value of the A parameter 0.b.sub.0 b.sub.1 . . . b.sub.i-1 b.sub.i . . . to bit b.sub.i-1 and adding `1` at the position of bit b.sub.i-1 to the truncated value of A;
• deriving means for deriving a symbol in response to the at least one probability value, and in response to a value for the A parameter and a value for the C parameter;
• means for updating the value of at least the A parameter in order to become the new size of the interval for decoding the next symbol of the information signal;
• means for outputting the derived symbol in an information signal including a sequence of n-bit symbols, n being an integer and n.gtoreq.1;
• means for storing the updated value for the A parameter in the first register.

Apparatus comprising:

• input means for receiving an arithmetically encoded information signal;
• finite sized first and second registers, the first register for storing an A parameter, the A parameter having a relationship with a size of a value interval, the second register for storing a C parameter, the contents of the second register before a decoding step being obtained from the contents of the second register obtained in a previous decoding step, by shifting m bits of the arithmetically encoded information signal into the second register, where m is a variable integer and m.gtoreq.0;
• generator means for generating at least one probability value for an associated symbol to be decoded;
• retrieval means for retrieving the values for the A and C parameters from the first and second registers, respectively, for truncating the value of the A parameter 0.b.sub.0 b.sub.1 . . . b.sub.i-1 b.sub.i . . . to bit b.sub.i-1, and for if b.sub.i-1 =`0` and b.sub.i =`1` then raising b.sub.i-1 to `1`.
• deriving means for deriving a symbol in response to the at least one probability value, and in response to a value for the A parameter and a value for the C parameter;
• means for updating the value of at least the A parameter in order to become the new size of the interval for decoding the next symbol of the information signal;
• means for outputting the decoded symbol in an information signal including a sequence of n-bit symbols, n being an integer and n.gtoreq.1;
• means for storing the updated value for the A parameter in the first register.

Apparatus comprising:

• input means for receiving an arithmetically encoded information signals;
• finite sized first and second registers, the first register for storing an A parameter, the A parameter having a relationship with the size of a value interval, the second register for storing a C parameter, the contents of the second register before a decoding step being obtained from the contents of the second register obtained in a previous decoding step, by shifting m bits of the arithmetically encoded information signal into the second register, where m is a variable integer and m.gtoreq.0;
• generator means for generating at least one probability value for an associated symbol to be decoded;
• retrieval means for retrieving the values for the A and C parameters from the first and second registers, respectively, truncating the value of the A parameter 0.b.sub.0 b.sub.1 . . . b.sub.i-1 b.sub.i . . . to the bit b.sub.i-1, and making bit b.sub.i-1 equal to `1`;
• deriving means for deriving a symbol in response to the at least one probability value, and in response to a value for the A parameter and a value for the C parameter;
• means for updating the value of at least the A parameter in order to become the new size of the interval for decoding the next symbol of the information signal;
• means for outputting the decoded symbol in an information signal including a sequence of n-bit symbols, n being an integer and n.gtoreq.1;
• means for storing the updated value for the A parameter in the first register.