Arithmetic Operations: Sub Word Parallelism

SUB WORD PARALLELISM

A subword is a lower precision unit of data contained within a word. In subword parallelism, multiple subwords are packed into a word and then process whole words. With the appropriate subword boundaries this technique results in parallel processing of subwords. Since the same instruction is applied to all subwords within the word, This is a form of SIMD(Single Instruction Multiple Data) processing.

It is possible to apply subword parallelism to noncontiguous subwords of different sizes within a word. In practical implementation is simple if subwords are same size and they are contiguous within a word. The data parallel programs that benefit from subword parallelism tend to process data that are of the same size.

For example if word size is 64bits and subwords sizes are 8,16 and 32 bits. Hence an instruction operates on eight 8bit subwords, four 16bit subwords, two 32bit subwords or one 64bit subword in parallel.

·        Subword parallelism is an efficient and flexible solution for media processing because algorithm exhibit a great deal of data parallelism on lower precision data.

·        It is also useful for computations unrelated to multimedia that exhibit data parallelism on lower precision data.

·       Graphics and audio applications can take advantage of performing simultaneous operations on short vectors