Macro Processors Chapter 5 1 Introduction l Concept

Macro Processors Chapter 5 1

Introduction l Concept » A macro instruction is a notational convenience for the programmer » It allows the programmer to write shorthand version of a program (module programming) » The macro processor replaces each macro invocation with the corresponding sequence of statements (expanding) 2

Macro Processor l l Recognize macro definitions Save the macro definition Recognize macro calls Expand macro calls Source Code (with macro) Macro Processor Expanded Code Compiler or Assembler obj 3

Macro Definition l l copy code parameter substitution conditional macro expansion macro instruction defining macros 4

Copy code -- Example Source STRG MACRO STA DATA 1 STB DATA 2 STX DATA 3 MEND. STRG. . Expanded source. . . STA DATA 1 STB DATA 2 STX DATA 3. { { 5

Macro vs. Subroutine l Macro » the statement of expansion are generated each time the macro are invoked l Subroutine » the statement in a subroutine appears only once 6

Parameter Substitution -- Example Source STRG MACRO &a 1, &a 2, &a 3 STA &a 1 STB &a 2 STX &a 3 MEND. STRG DATA 1, DATA 2, DATA 3. STRG DATA 4, DATA 5, DATA 6. . Expanded souce. . . STA STB STX. { { DATA 1 DATA 2 DATA 3 DATA 4 DATA 5 DATA 6 7

Parameter Substitution l Dummy arguments » Positional argument STRG DATA 1, DATA 2, DATA 3 GENER , , DIRECT, , , 3 » Keyword argument STRG &a 3=DATA 1, &a 2=DATA 2, &a 1=DATA 3 GENER TYPE=DIRECT, CHANNEL=3 l Example: Fig. 4. 1, Fig. 4. 2 » Labels are avoided in macro definition 8

One-Pass Macro Processor l Prerequisite » every macro must be defined before it is called l Sub-procedures » macro definition: DEFINE » macro invocation: EXPAND NAMTAB MACRO DEFINE DEFTAB CALL EXPAND ARGTAB PROCESSLINE 9

Data Structures -- Global Variables l l l DEFTAB NAMTAB ARGTAB EXPANDING 11

ARGTAB 1 F 1 2 BUFFER 3 LENGTH 12

Nested Macros Definition l Macro definition within macros » process macro definition during expansion time l Example 4. 3 13

Figure 4. 3 (b) 14

One-Pass Macro Processor That Allows Nested Macro Definition l Sub-procedures » macro definition: DEFINE » macro invocation: EXPAND l EXPAND may invoke DEFINE when encounter macro definition NAMTAB DEFTAB ARGTAB Expanding MACRO DEFINE CALL EXPAND PROCESSLINE MACRO Definition 15

1 -Pass Macro Processor 18

Comparison of Macro Processors Design l Single pass » every macro must be defined before it is called » one-pass processor can alternate between macro definition and macro expansion » nested macro definitions may be allowed but nested calls are not l Two pass algorithm » Pass 1: Recognize macro definitions » Pass 2: Recognize macro calls » nested macro definitions are not allowed 19

Machine Independent Macro Processor Feature 20

Concatenation of Macro Parameters l Pre-concatenation » LDA l Post-concatenation » LDA l X&ID 1 Example: Figure 4. 6 21

Generation of Unique Labels l Example » JEQ *-3 » inconvenient, error-prone, difficult to read l Example Figure 4. 7 – $LOOP TD =X’&INDEV’ TD =X’F 1’ » 1 st call: – $AALOOP » 2 nd call: – $ABLOOP 22

RDBUFF F 1, BUFFER, LENGTH

Conditional Macro Expansion l Macro-time conditional statements » Example: Figure 4. 8 » IF-ELSE-ENDIF l Macro-time variables » any symbol that begins with the character & and that is not a macro parameter » macro-time variables are initialized to 0 » macro-time variables can be changed with their values using SET – &EORCK SET 1 25

RDBUFF F 3, BUF, RECL, 04, 2048 RDBUFF 0 E, BUFFER, LENGTH, , 80

RDBUFF F 1, BUFF, RLENG, 04

Conditional Macro Expansion (Cont. ) l Macro-time looping statement » Example: Figure 4. 9 » WHILE-ENDW l Macro processor function » %NITEMS: THE NUMBER OF MEMBERS IN AN ARGUMENT LIST 29

Nested Macro Invocations l Macro invocations within macros » process macro invocation during expansion time l Recursive macro expansion » Example: Figure 4. 11 » Problems: – ARGTAB – EXPANDING » Solution – Recursive call – While loop with stack 30

ARGTAB DEFTAB MACRO Definition NAMTAB DEFINE GETLINE PROCESSLINE Macro Invocation EXPAND ARGTAB 31

1 -Pass Macro Processor 32

Allowing Nested Macro Invocation 33

Macro-Assembler l Advantage » reduce 1 pass » share same data structure l Disadvantage » more complex 34

Pass 1 R READ Search (Pseudo-Op Table) Type? Search NAMTAB (Macro Name Table) MACRO Define Process pseudo-ops Search (Machine Op Table) R R Process machine instruction MACRO Expand R R Pass 2

General Purpose Macro Processor l ELENA » Software: Practice and Experience, Vol. 14, pp. 519 -531, Jun. 1984 l Macro definition » header: – a sequence of keywords and parameter markers (%) – at least one of the first two tokens in a macro header must be a keyword, not a parameter marker » body: – the character & identifies a local label – macro time instruction (. SET, . IF. JUMP, . E) – macro time variables or labels (. ) 36

ELENA (cont. ) l Macro invocation » There is no single token that constitutes the macro “name” » Constructing an index of all macro headers according to the keywords in the first two tokens of the header » Example – DEFINITION: l l ADD %1 TO %2 ADD %1 TO THE FIRST ELEMENT OF %2 – INVOCATION: l DISPLAY TABLE DISPLAY %1 %1 TABLE 37