1. A method of executing an instruction set to select a set of registers, the method comprising: reading a first instruction of the instruction set; interpreting a first operand of the first instruction to represent a first register S of said set of registers to be selected, where S is an integer; interpreting a second operand of the first instruction to represent a number N of registers to be selected; selecting N consecutive registers starting at the first register S to form the set of registers; reading a second instruction of the instruction set; determining that the second instruction is not integral with the first instruction; reading a third instruction and a fourth instruction of the instruction set; determining that the third instruction is integral with the fourth instruction; interpreting an operand of the fourth instruction to be a bitmap in which each bit corresponds to a register; and selecting those registers for which the corresponding bit has a predetermined value.