Microprocessor designers have increasingly endeavored to improve performance in various microprocessors by defining an instruction which does a common function in order to save executing a number of instructions to perform the same function. For this reason, some microprocessors have an instruction for setting a selected bit field in an operand to all 1's, or for clearing a selected bit field in the operand to all 0's. Typically, a sequence of microcode instructions is used to implement such a bit field instruction by shifting 0's or 1's, as appropriate, into the operand at a designated location. As a result, several iterative cycles are required to execute a bit field instruction.
An object of the present invention is to overcome the performance delay caused by iterative execution of microcode for a bit field instruction.