Decoding base instructions modified by a prefix instruction using modifier bits

摘要

A method 300 for decoding instructions in a computer program wherein the instructions comprise one or more base instructions that are subject to modification by one or more other instructions. An instruction comprising one or more modifier bits is received 302 at a decoder. The decoder 304 analyses the modifier bits to determine whether the received instruction is a base instruction 306 (i.e. an instruction subject to modification by one or more other instructions). If the received instruction is determined to be a base instruction the decoder determines whether there are a predetermined number of stored prefix instructions for the base instruction 314. If there is not the predetermined number of stored prefix instructions for the base instruction an error has occurred and exception handling code is invoked 320.