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

    Purpose:        Subtract one packed decimal string from a second
    Format:         opcode sublen.rw,subaddr.ab,
                           diflen.rw,difaddr.ab                 ;4 operand
                    opcode sublen.rw,subaddr.ab,minlen.rw,
                           minaddr.ab,diflen.rw,difaddr.ab      ;6 operand
    Operation:      {dif string} = {dif string} - {sub string}  ;4 operand
                    {dif string} = {min string} - {sub string}  ;6 operand
    C. Codes:       N = {{dif string} LSS 0}, V = {decimal overflow},
                    Z = {{dif string} EQL 0}, C = 0
    Exceptions:     Reserved operand, decimal overflow
    Opcode:         25    SUBP4    Subtract packed 4 operand
                    23    SUBP6    Subtract packed 6 operand
    Description:    sub as specified by subaddr and sublen is subtracted
                    from dif as specified by difaddr and diflen (in 4
                    operand form) or min as specified by minaddr and
                    minlen (in 6 operand form) and the result is placed
                    in dif.
    Notes:          After execution of SUBP4:

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

                    After execution of SUBP6:

                    R0 = 0
                    R1 = address of the byte containing the
                         most-significant digit of the subtrahend string
                    R2 = 0
                    R3 = address of the byte containing the
                         most-significant digit of the minuend string
                    R4 = 0
                    R5 = address of the byte containing the
                         most-significant digit of the difference string