can someone explaine this to me? Given a macro definition as the following, what

Question

can someone explaine this to me?

Given a macro definition as the following, what is the expansion result of a macro 7. invocation like "RDBUFF oE,BUFFER,LENGTH..80"? (5%) RDBUFF MACRO &INDEV;, &BUFADR; &RECLTH; &EOR;,&MAXLTH; (&EOR; NE IF &EORCK; ENDIF CLEAR LOOP COUNTER CLEAR X CLEAR A (&EORCK; EQ 1) IF LDCH XT&EOR;' SET EOR CHARACTER RMO A, S ENDIF (&MAXLTH; EQ LDT #4096 SET MAX LENGTH 4096 ELSE SET MAXIMUM RECORD LENGTH +LDT H&MAXLTH; ENDIF SLOOP TD X &INDEV; TEST IN PUT DEVICE JEQ SLOOP LOOP UNTIL READY RD X &INDEV;" READ CHARACTER INTO REG A (&EORCK; EQ 1) COMPR AS TEST FOR END OF RECORD JEQ EXIT LOOP IF EOR ENDIF STCH &BUFADR; X STORE CHARACTER IN BUFFER TIXR. T LOOP UNLESS MAXIMUM LENGTH JLT SLOOP HAS BEEN REACHED SEXIT STX &RECLTH; SAVE RECORD LENGTH MEND

Explanation / Answer

Macro Processors:

Macro is a unit of specification for program generation through expansion. A macro represents a commonly used group of statements in the source programming language.The macro processor replaces each macro instruction with the corresponding group of source language statements. This is called expanding of macros.

A macro consists of a name , a set of formal parameters and body of code.

Macro definitions consists of

(1). Macro prototype   (2). One or more model (3). Macro processor

Macro definition is in between a macro header statement and macro end statement.

Syntax of macro prototype statement:-

<macro name> [ < formal parameter spec > [ ;...]]

where

< macro name > = it is in the mnemonic field of an assembly statement

< formal parameter spec > is in the following form

< parameter name > [ < parameter kind > ]

Syntax of the macro call is

< macro name > [ < actual parameter spec > [;..]]

Macro Expansion:-

           (a). Expansion time control flow

           (b). Lexical substitution

Algorithm for Macro Expansion:-

1. Initialise the macro expansion counter (MEC).

2. Check the statement which is pointed MEC is not a mend statement.

(a) if statement is model statement

                 then expand the statement and

                   increment the MAC by 1

      else

      MAC:= new value specified in the statement

3. Exit from the macro expansion.

Solution:-

                             RDBUFF F31 , BUF, RECL , 04, 2048

                             CLEAR           X                                CLEAR LOOP COUNTER

                             CLEAR           A

                             LDCH            =X'04'                         SET EOR CHARACTER

                             RMO             A,S

                            +LDT             #2048                        SET MAXIMUM RECORD LENGTH

            $AALOOP TD =X'F3'    TEST INPUT DEVICE

   JEQ $AALOOP    LOOP UNTIL READY

   RD =X'F3'    READ CHARACTER INTI REG A

COMPR    A,S                           TEST FOR END OF RECORD

                         JEQ              $AAEXIT                      EXIT LOOP IF EOR

                         STCH           BUF, X                          STORE CHARACTER IN BUFFER

                         TIXR                T                               LOOP UNLESS MAXIMUM LENGTH

                         JLT              $AALOOP                    HAS BEEN REACHED

       $AAEXIT    STX                RECL                          SAVE RECORD LENGTH

* Hope you know the basic macro syntax                  

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