Data compression and decompression

A computer-implemented method for decompressing, compressed data, the compressed data comprising an m-bit encoding representing the two least significant bits of each decompressed data value of a group of m decompressed data values, wherein the m-bit encoding is from either:

• (i) a first group of encodings comprising (2m−4) m-bit encodings, or (ii) a second group of encodings comprising four m-bit encodings, the method comprising:
• mapping the m-bit encoding onto 2m output bits representing the two least significant bits of each of the m decompressed data values,
• wherein if the m-bit encoding is from the first group of encodings, the 2m output bits representing the two least significant bits of each of the m decompressed data values comprise:
• (i) a second least significant bit of each of the m decompressed data values which is equal to a respective bit of the m-bit encoding, and (ii) a least significant bit for each of the m decompressed data values, and
• wherein if the m-bit encoding is from the second group of encodings, the two least significant bits of each of the m decompressed data values represented by the 2m output bits are equal to the two least significant bits of the other ones of the m decompressed data values represented by the 2m output bits.

A decompression unit configured to decompress compressed data, the compressed data comprising an m-bit encoding representing the two least significant bits of each decompressed data value of a group of m decompressed data values, wherein the m-bit encoding is from either:

• (i) a first group of encodings comprising (2m−4) m-bit encodings, or (ii) a second group of encodings comprising four m-bit encodings, the decompression unit comprising:
• mapping logic configured to map the m-bit encoding onto 2m output bits representing the two least significant bits of each of the m decompressed data values, wherein the mapping logic is configured such that:
• when the m-bit encoding is from the first group of encodings, the 2m output bits representing the two least significant bits of each of the m decompressed data values comprise:
• (i) a second least significant bit of each of the m decompressed data values which is equal to a respective bit of the m-bit encoding, and (ii) a least significant bit for each of the m decompressed data values, and
• when the m-bit encoding is from the second group of encodings, the two least significant bits of each of the m decompressed data values represented by the 2m output bits are equal to the two least significant bits of the other ones of the m decompressed data values represented by the 2m output bits.