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

    Purpose:        Compare two character strings
    Format:         opcode len.rw,src1addr.ab,src2addr.ab       ;3 operand
                    opcode src1len.rw,src1addr.ab,fill.rb       ;5 operand
                      src2len.rw,src2addr.ab
    Operation:      {compare two strings with optional filling}
    C. Codes:       [final codes reflect last affecting of codes
                     in the operation.]
                    N = {{first byte} LSS {second byte}}, Z =
                    {{first byte} EQL {second byte}}, V = 0,
                    C = {{first byte} LSSU {second byte}}
    Exceptions:     None
    Opcodes:        29    CMPC3    Compare character 3 operand
                    2D    CMPC5    Compare character 5 operand
    Description:    In 3-operand format the bytes of string 1 specified
                    by len and src1addr are compared with string 2
                    specified by len and src2addr. In 5-operand format
                    the bytes of string 1 specified by src1len and
                    src1addr are compared with string 2 specified by
                    src2len and src2addr. If one string is longer than
                    the other the shorter string is conceptually
                    extended by appending bytes with the value of fill
                    to the end. Comparison proceeds until all the bytes
                    have been examined or inequality is detected.
                    Condition codes are affected by the last character
                    comparison.
    Notes:         After execution of CMPC3:

                    R0 = number of bytes remaining in string 1 (including
                         byte that terminated comparison); R0 is 0
                         only is strings are equal
                    R1 = address of the byte in string 1 that
                         terminated comparison; if strings are equal,
                         address of one byte beyond string 1
                    R2 = R0
                    R3 = address of the byte in string 2 that
                         terminated comparison; if strings are equal,
                         address of one byte beyond string 2

           After execution of CMPC5:

                    R0 = number of bytes remaining in string 1 (including
                         byte that terminated comparison); R0 is 0
                         only if string1 and string 2 are of equal length
                         or string 1 was exhausted before comparison
                         terminated
                    R1 = address of the byte in string 1 that
                         terminated comparison; if comparison did not
                         terminate before string 1 exhausted,
                         address of one byte beyond string 1
                    R2 = number of bytes remaining in string 2 (including
                         byte that terminated comparison); R2 is 0 only
                         if string 1  and string 2 are of equal length or
                         string 2 was exhausted before comparison terminated
                    R3 = address of the byte in string 2 that
                         terminated comparison; if conmparison did not
                         terminate before string 2 was exhausted,
                         address of one byte beyond string 2