VMS Help MACRO, VAX MACRO Assembler, Instructions, ADDPx  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Purpose:        Add one packed decimal string to another
    Format:         opcode addlen.rw,addaddr.ab,
                      sumlen.rw, sumaddr.ab                  ;4 operand
                    opcode add1len.rw,add1addr.ab,add2len.rw,
                      add2addr.ab,sumlen.rw,sumaddr.ab       ;6 operand
    Operation:      {sum string} = {sum string} +
                      {add string}                           ;4 operand
                    {sum string} = {add1 string} +
                      {add2 string}                          ;6 operand
    C. Codes:       N = {{sum string} LSS 0}, Z = {{sum string} EQL 0},
                    V = {decimal overflow}, C = 0
    Exceptions:     Reserved operand, decimal overflow
    Opcodes:        80    ADDP4    Add packed 4 operand
                    81    ADDP6    Add packed 6 operand
    Description:    In 4 operand format, the addend string as specified
                    by addlen and addaddr is added to the sum string
                    specified by sumlen and sumaddr, and sum is replaced
                    by the result. In 6 operand format, the addend 1
                    string specified by add1len and add1addr is added to
                    the addend 2 string specified by add2len and
                    add2addr, and the sum string is replaced by the
                    result.

               Notes:          After execution of ADDP4:

                    R0 = 0
                    R1 = address of the byte containing the
                         most-significant digit of the addend string
                    R2 = 0
                    R3 = address of the byte containing the
                         most-significant digit of the sum string

                    After execution of ADDP6:

                    R0 = 0
                    R1 = address of the byte containing the
                         most-significant digit of the addend 1 string
                    R2 = 0
                    R3 = address of the byte containing the
                         most-significant digit of the addend 2 string
                    R4 = 0
                    R5 = address of the byte containing the
                         most-significant digit of the sum string