Macro exit directive

    Format

      .MEXIT

1  –  Description

    .MEXIT terminates a macro expansion before the end of the macro.
    Termination is the same as if .ENDM were encountered. You can
    also use the directive within repeat blocks. .MEXIT is useful
    in conditional expansion of macros and repeat blocks because it
    bypasses the complexities of nested conditional directives and
    alternate assembly paths.

2  –  Notes

    o  When .MEXIT occurs in a repeat block, the assembler terminates
       the current repetition of the range and suppresses further
       expansion of the repeat range.

    o  When macros or repeat blocks are nested, .MEXIT exits to the
       next higher level of expansion.

    o  If .MEXIT occurs outside a macro definition or a repeat block,
       the assembler displays an error message.

3  –  Examples

      Example 1
      The following macro definition uses the .MEXIT directive
      to exit the current macro when it has finished processing a
      particular kind of argument:

                .macro STORE REG, LOCATION
                    .if identical,<REG>,<FP>
                        STQ REG, LOCATION
                        .mexit
                    .endc
                    .if identical,<REG>,<SP>
                        STQ REG, LOCATION
                        .mexit
                    .endc
                    .if identical,<%extract(0,1,<REG>)>,<R>
                        STQ REG, LOCATION
                        .mexit
                    .endc
                    .if identical,<%extract(0,1,<REG>)>,<F>
                        STT REG, LOCATION
                        .mexit
                    .endc
                    .error "Register argument is not a register"
                .endm STORE

      Example 2
      In this example, the STORE macro (as defined in Example 1)
      attempts to recognize its REG argument as either FP, SP, an
      integer register (a register with R as its first letter),
      or a floating-point register (a register with F as its first
      letter). The following example show two expansions of the STORE
      macro:

                STORE R1, 0(SP)
                    .if identical,<R1>,<FP>
                    .endc
                    .if identical,<R1>,<SP>
                    .endc
                    .if identical,<%extract(0,1,<R1>)>, <R>
                    .if identical,<R>,<R>
                        STQ R1, 0(SP)
                        .mexit

                STORE 24(SP), 16(SP)
                    .if identical,<24(SP)>,<FP>
                    .endc
                    .if identical,<24(SP)>,<SP>
                    .endc
                    .if identical,<%extract(0,1,<24(SP)>)>,<R>
                    .if identical,<2>,<R>
                    .endc
                    .if identical, <%extract(0,1<24(SP)>)>,<F>
                    .if identical,<2>,<F>
                    .endc
                    .error "Register argument is not a register"

      The first call of the STORE macro stores R1 at 0(SP). The
      STORE macro determines to do an integer store by recognizing
      the letter R as the first letter of the register name. After
      it has done so, it abandons further expansion of the macro
      using the .MEXIT directive. The second invocation attempts to
      store 24(SP) at 16(SP). Since the STORE macro cannot identify
      24(SP) as a legitimate register in any of the four forms it
      recognizes, the STORE macro does not attempt to store the
      REG argument, and does not abandon expansion with the .MEXIT
      directive. Instead, the STORE macro expands and issues a
      diagnostic message.