1. A method comprising: detecting a sign assignment instruction having an input operand and an output operand identical in size to each other, the sign assignment instruction operating on an input operand having a packed decimal format, the sign assignment instruction operating to assign a value of zero to a packed decimal data value of the input operand having a value of negative zero; analyzing, based on the detecting, the input operand of the sign assignment instruction to determine whether a value of the input operand results from an add or subtract operation and whether the value is greater than the value prior to the operation; and based on the analyzing determining at least one of one of that the value of the input operand does not result from an add or subtract operation or that the value is not greater than the value prior to the operation, checking, based on the input operand and the output operand of the sign assignment instruction having identical addresses, a possibility that the value of the input operand of the sign assignment instruction is negative zero; and generating and inserting an instruction for executing the sign assignment instruction only when there is the possibility that the value is negative zero.