Data replacement method and circuit for motion prediction cache

A method for replacing image data in a motion prediction cache comprised of a plurality of cache lines, the method comprising:

• for each of the cache lines, calculating a tag distance between pixels stored in the cache line and uncached pixels that are to be stored in the motion prediction cache;
• comparing the tag distances to each other to determine a maximum tag distance;
• and
• replacing the pixels in one of the cache lines having the maximum tag distance with the uncached pixels.

A system for decoding a video bitstream comprising:

• a motion prediction cache having a data memory for storing a plurality of cache lines and having a tag memory for storing a plurality of tag entries wherein each tag entry includes at least one attribute of a respective one of the cache lines, the tag memory being organized as a plurality of sets defined according to the at least one attribute;
• a control module in communication with the motion prediction cache and adapted to receive a request for a cache line, the request indicating at least one attribute of the cache line, wherein the control module searches one of the sets according to the at least one attribute to determine whether a tag entry for the requested cache line is in the tag memory and determines a tag distance for each of the tag entries in the set if the tag entry is not in the tag memory;
• and
• a state machine in communication with the motion prediction cache and configured to identify one of the cache lines in the data memory for replacement by the requested cache line if the tag entry for the requested cache line is not in the tag memory.