Patent ID: 8378861

Claim:
An apparatus for processing data comprising: processing circuitry configured to perform processing using arithmetic coding, said arithmetic coding transforming between a stream of data values and a stream of coded data values and using a plurality of contexts, each of said plurality of contexts having a context index value and one or more associated probability values, said probability values each indicating, for a current context reached in said stream of data values, a probability that a next data value within said stream will have a predicted value associated with that probability; a probability value memory configured to store said one or more probability values for said plurality of contexts; and a cache memory, coupled to said processing circuitry and to said probability value memory, configured to cache from said probability value memory said one or more probability values for each of a group of contexts from within said plurality of contexts and to be addressed for access by said processing circuitry with a current context index value associated with said current context; wherein at least some of said context index values are mapped to said plurality of contexts such that context index values used to process data values close by in position within said stream of data values have a greater statistical likelihood of sharing a group of contexts than context index values used to process data values far away in position within said stream of data values.