Data processing systems

An apparatus for determining a data value to use for a data position of a stored data array in a data processing system, the apparatus comprising:

• reading circuitry configured to read a stored header data block for a block of the data array that the data position falls within;
• determining circuitry configured to determine whether the header data block contains an indication that all of the data positions for the block of the data array have the same data value;
• and the determining circuitry is further configured to, when it is determined from the header data block that all of the data positions of the stored data array for the block of the data array that the header data block relates to have the same data value:
• determine from other data stored in the header data block the value to use for the data position.

A computer readable storage medium storing computer software code which when executing on at least one processor performs a method of determining a data value to use for a data position of a stored data array in a data processing system, the method comprising:

• reading by processing circuitry a stored header data block for a block of the data array that the data position falls within;
• determining by processing circuitry whether the header data block contains an indication that all of the data positions for the block of the data array have the same data value;
• and, when it is determined from the header data block that all of the data positions of the stored data array for the block of the data array that the header data block relates to have the same data value:
• determining by processing circuitry from other data stored in the header data block the value to use for the data position.