add

    OpenVMS usage:word_signed
    type:         word (signed)
    access:       read only
    mechanism:    by reference

    The addend operand to be added to the value of sum. The add
    argument is the address of a signed word that contains the addend
    operand.

 sum

    OpenVMS usage:word_signed
    type:         word integer (signed)
    access:       modify
    mechanism:    by reference

    The word to which add is added. The sum argument is the address
    of a signed word integer containing this value. The add operand
    is added to the sum operand, and the value of the sum argument is
    replaced by the result of this addition. The sum argument must be
    word-aligned; in other words, its address must be a multiple of
    2.

 sign

    OpenVMS usage:word_signed
    type:         word integer (signed)
    access:       write only
    mechanism:    by reference

    Sign of the sum argument. The sign argument is the address of
    a signed word integer that is assigned the value -1, 0, or 1,
    depending on whether the new value of sum is negative, 0, or
    positive.