1. A computer program product for executing a machine instruction in a central processing unit, the computer program product comprising: a computer readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: obtaining, by a processor, a machine instruction for execution, the machine instruction being defined for computer execution according to a computer architecture, the machine instruction comprising: at least one opcode field to provide an opcode, the opcode identifying a Vector Generate Mask operation; a first register field to be used to designate a first register, the first register comprising a first operand; a first field to specify a starting position; and a second field to specify an ending position; and executing the machine instruction, the executing comprising: generating a mask for one or more elements of the first operand, the generating comprising setting one or more positions in the mask to a predefined value beginning at the starting position in the mask and ending at the ending position.