Introduction, Macro Definition and Call, Macro Expansion, Nested Macro Calls, Advanced Macro Facilities, Design Of a Macro Preprocessor, Design of a Macro Assembler, Functions of a Macro Processor, Basic Tasks of a Macro Processor, Design Issues of Macro Processors, Features, Macro Processor Design Options, Two-Pass Macro Processors, One-Pass Macro Processors

1. Subject-System Programming
Sub. Code-2150708
Unit- 4 (Macro and Macro pre-
processor)
By- Prof. Deepmala Sharma
MBICT CVM group, Anand
(V.V.Nagar)

2. Contents
• What is Macro?
• Advantages and disadvantages of Macro
• Applications of Macro
• Difference between Macro and Subroutines
• Macro Definition and Call
• Macro Expansion
• Handling Macro calls and Macro expansion
• Features of Macro facility
– Lexical expansion and parameter substitution
– Nested Macro Calls
– Advanced Macro Facilities
• Design Of a Macro Pre-processor
– Functions of a Macro Processor
– Basic Tasks of a Macro Processor
– Design Issues of Macro Processors,
– Features,
– Macro Processor Design Options,
– Two-Pass Macro Processors, and One-Pass Macro Processors
• Design of a Macro Assembler

3. Macro and Macro processor
• Macro:-
– Macro instructions are single line abbreviations for group
of instructions.
– Using a macro, programmer can define a single
“instruction” to represent block of code.
– Ex: #define in C and MACRO <Macro Name> in Assembly
language
• Macro processor-
– Macro instructions are an extension of the basic assembly
language that can simplify debugging and program
modification during translation.
– To process macro instructions , most assembler use pre-
processors known as Macro processors

4. Advantages and Disadvantages
• The advantages of using macro are as follows:
– Simplify and reduce the amount of repetitive coding.
– Reduce the possibility of errors caused by repetitive
coding
– Make an assembly program more readable
• The disadvantage of the macro is the size of the
program. The reason is, the pre-processor will
replace all the macros in the program by its real
definition prior to the compilation process of the
program.

5. Applications of Macro
• when assembly language programming was
commonly used to write programs for digital
computers
• the use of macro instructions was initiated for
two main purposes:
• to reduce the amount of program coding that
had to be written by generating several
assembly language statements from one
macro instruction

6. MACROS PROCEDURE
1
The corresponding machine code
is written every time a macro is
called in a program.
1 The Corresponding m/c code is
written only once in memory
2
Program takes up more memory
space.
2 Program takes up comparatively
less memory space.
3
No transfer of program counter. 3 Transferring of program counter is
required.
4
No overhead of using stack for
transferring control.
4 Overhead of using stack for
transferring control.
5
Execution is fast 5 Execution is comparatively slow.
6
Assembly time is more. 6 Assembly time is comparatively
less.
7
More advantageous to the
programs when repeated group of
instruction is too short.
7 More advantageous to the
programs when repeated group of
instructions is quite large.
Difference between MACRO and PROCEDURE

7. Difference between MACRO and Subroutine

8. Design of Macro pre-processor

9. Macro definition and call
• A macro is a unit of specification for program generation
through expansion.
• A macro consists of a name, a set of formal parameters and
a body of code.
• The use of macro name with a set of actual parameters is
replaced by code generated from its body.
• The formal structure of a macro includes the following
features:
– Macro prototype statement: Specifies the name of the macro
and type of formal parameters.
– Model statements: Specify the statements in the body of the
macro from which assembly language statements are to be
generated during expansion.
– Macro preprocessor statement: Specifies the statement used
for performing auxiliary function during macro expansion

10. Macro Statements
• A macro prototype statement
• where [<formal parameter spec> [,...]] defines
the parameter name and its kind, which are of
the following form:
• A macro can be called by writing the name of the
macro in the mnemonic field of the assembly
language called macro call
• macro call Statement:

11. Example of macro definition and call
• Macro Definition
• Macro Call
Name of macro
Start of definition
Sequence of instructions
End of definition

12. Macro Expansion
• Replacement of macro call by corresponding sequence
of instructions is called as macro expansion
• To expand a macro, the name of the macro is placed in
the operation field, and no special directives are
necessary.
• The assembly code sequence INCR A, B, AREG
is an example of the macro call
• the assembler recognizes INCR as the name of the
macro, expands the macro, and places a copy of the
macro definition (along with the parameter
substitutions)
• ‘+’ sign in the preceding label field denote the
expanded code

13. Example
MACRO
INCR &A, &B, AREG
MOVER REG &A
ADD REG & B
MOVEM REG & A
MEND
Macro definitionMacro call
 A and B are an actual
parameters
 &A and &B are formal
parameters
Macro call
Expanded code

14. First Macro Example:-
#include <stdio.h>
#define SquareOf(x) x*x // (Macro definition)
void main() {
int xin=3;
printf("nxin=%i",xin);
printf("nSquareOf(xin)=%i",SquareOf(xin)); // (macro call)
printf("nSquareOf(xin+4)=%i",SquareOf(xin+4));
printf("nSquareOf(xin+xin)=%i",SquareOf(xin+xin));
}

15. Lexical Expansion and Parameter
Substitution (Lexical Substitution)
• Two key points concerning macro expansion
are:
– Expansion time control flow: This determines the
order in which model statements (body) are
visited during macro expansion.
– Lexical Substitution: It is used to generate an
assembly statement from a model
statement(body).

16. Four ways of specifying arguments to
a macro call (Parameter Substitution)
• A) Positional argument or Parameter
Argument are matched with dummy arguments
according to order in which they appear or
compute the ordinal position of the formal
parameters.
• INCR A,B,C
• ‘A’ replaces first dummy argument
• ‘B’ replaces second dummy argument
• ‘C’ replaces third dummy argument

17. Example
• Macro definition
– MACRO
– MNAME &par1, &par2, &par3
– MOVER &par1, &par2
– ADD &par1, &par3
– MOVEM &par1, &par2
– MEND
• Macro call
– MNAME REG1, A, B
• Expanded code
– MOVER REG1, A
– ADD REG1, B
– MOVEM REG1, A
Formal Par Actual par
&par1 REG1
&par2 A
&par3 B

18. • B) keyword arguments or parameters
• This allows reference to dummy arguments by
name as well as by position.
• The parameter specification are useful when
macros use a long list of parameters
• Format: &<name_of_par>=<actual_par>

19. Example
• Macro definition
– MACRO
– MNAME &par1=, &par2=, &par3=
– MOVER &par1, &par2
– ADD &par1, &par3
– MOVEM &par1, &par2
– MEND
• Macro call
– 1. MNAME par1=REG1, par2=A, par3=B OR
– 2. MNAME par1=A, par2=REG1, par3=B
• 1. Expanded code
– MOVER REG1, A
– ADD REG1, B OR
– MOVEM REG1, A
2. Expanded code
MOVER A, REG1
ADD A, B
MOVEM A, REG1

20. • C) keyword Default Parameters
• If a parameter has the same value in most calls
on a macro, this value can be specified as its
default value in the macro definition itself.
• If a macro call does not explicitly specify the value
of the parameter, the pre-processor uses its
default value; otherwise, it uses the value
specified in the macro call.
• Par. spec. required when the parameter takes the
same value in most calls.
• Format :

21. Example
• Macro definition
– MACRO
– MNAME &par1= REG1, &par2=, &par3=
– MOVER &par1, &par2
– ADD &par1, &par3
– MOVEM &par1, &par2
– MEND
• Macro call
– 1. MNAME par2=A, par3=B OR
– 2. MNAME par1=REG2, par2=A, par3=B
• 1. Expanded code
– MOVER REG1, A
– ADD REG1, B OR
– MOVEM REG1, A
2. Expanded code
MOVER REG2, A
ADD REG2, B
MOVEM REG2, A

22. • d) Mixed Parameters
• A macro definition may use both positional and
keyword parameters. In such a case, all
• positional parameters must precede all keyword
parameters in a macro call
• This makes the search and association of the
actual parameters to the corresponding formal
parameter easier.
• The parameters can be used not only in the
operation field, but also in all the field of the
instruction

23. Example
• Macro definition
– MACRO
– MCALC &par1=, &par2=, &par3=MULT, &par4=
– &par4
– MOVER REG1, &par1
– ADD REG1, &par2
– MOVEM REG1, &par1
– MEND
• Macro call
– MCALC A, B, par4=loop
• 1. Expanded code
– +loop MOVER REG1, A
– MULT REG1, B
– MOVEM REG1, A

24. Flow of control during macro
expansion
• Flow of control during expansion.
– The default flow of control during macro expansion is
sequential. its start with statement following the
macro prototype statement and ending with the
statement preceding the MEND statement.
– A pre-processor statement can alter the flow of
control during expansion such that some model
statements are never visited during expansion is called
conditional expansion.
– Same statement are repeatedly visited during
expansion is called loops expansion.

25. Flow of control during macro
expansion
• The flow of control during macro expansion is
implemented using a macro expansion counter (MEC)
• Algorithm of macro expansion:
• 1. MEC:=statement number of first statement following
the prototype stmt.
• 2. While statement pointed by MEC is not a MEND
statement.
– a. If a model statement then
• i. Expand the statement
• ii. MEC:=MEC+1;
– b. Else (i.e. a pre-processor statement)
• i. MEC:= new value specified in the statement.
• 3. Exit from macro expansion.

26. Nested Macro Facility
• Nested Macro Definition:
• Nested macro definition are those cases where the definition of
one macro is contained within the definition of another
• Example :
• MACRO
• MAC_X &par1, &par2
• MOVER REG1, &par1
– MACRO
– MAC_Y &par2, REG=REG3
– ADD REG, &par2
– MOVEM REG, &par2
– MEND
• PRINT &par1
• MEND

27. Nested Macro Facility
• Nested Macro Expansion and Call:
• A model statement in a macro may constitute a
call on another macro.
• Such calls are known as nested macro calls
• Macro containing the nested call is the outer
macro and, Macro called is inner macro
• They follow LIFO rule.
• Thus, in structure of nested macro calls,
• expansion of latest macro call (i.e inner macro) is
• completed first.

28. Example
• MACRO
– MAC_Y &par2, REG=REG3
– ADD REG, &par2
– MOVEM REG, &par2
– MEND
• MACRO
– MAC_X &par1, &par2
– MOVER REG1, &par1
– MAC_Y &par2, REG=REG3
• PRINT &par1
• MEND

29. Nested Expansion
Macro call Expansion Nested expansion
MAC_X A, B + MOVER REG1, A + MOVER REG1, A
+MAC_Y B, REG2 ++ADD REG2, B
+PRINT A ++ MOVEM REG2, B
+PRINT A

30. Recursive macro call
• A recursive macro is a situation where the macro
expands itself.
• Note: Macro definition does not contain any statement
to stop any of the inner expansions and return to
complete the outer ones. This lead to infinite loop.
• The conditional statement is one mechanism to handle
recursive call
• MACRO
– MAC_Y &par=A
– MOVER REG1, &par
– MAC_Y &par=A
• MEND

31. ADVANCED MACRO FACILITIES
• Facilities for change of flow of control
• Expansion time variables
• Attributes of parameters
• Advance directives
– The Remove Directive
– The IRP Directive
– The REPEAT Directive

32. For change of flow of control:-
Two features are provided for this purpose
1) Expansion time Sequencing Symbol
2) Expansion time Statements ( AIF,AGO,ANOP)
Sequencing Symbol( SS)
SS is defined by putting it in the label field of a stmt in the macro
body.
Statements (syntax)
AIF-> AIF ( <expression>) <Sequencing Symbol (SS)>
Expression includes relational expression ( LT, NE etc.). If condition
is true then control is transferred to SS.
AGO-> AGO <SS>  unconditional transfer
ANOP-> <SS> ANOP  used to define SS

33. Example
MACRO
TEST &X, &Y, &Z
AIF (&Y EQ &X) .ONLY
MOVER AREG, &Y
AGO .LAST
.ONLY MOVER AREG, &Z
.LAST MEND
REPRESENTING SS
If condition is true ( Y= X) then control will be transferred
to .ONLY

34. Expansion time variables
EV’s are variables which can be only used during the expansion
of macro calls.
It may be of two types:-
1) Local EV (LCL) can be used only in one particular macro.
2) Global EV (GBL) works like global variables.
Syntax:-
LCL <EV specification>, ………
GBL <EV specification>, ……..
Values of EV can be changed using SET (preprocessor stmt).
<EV specification> SET <SET expression>

35. Example of EV
MACRO
TESTEV
LCL &A
&A SET 1
LCL &A declares local variable A

36. Attributes of parameters
An attribute is written using the syntax:-
<attribute name> ’ <formal parameter specification>
T– type
L – length
S – size
Example
MACRO
ME &A
AIF (L’&A EQ 1) .NEXT
------
-----

37. EXAMPLE
MACRO
TEST &X, &N, R=AREG
LCL &M
&M SET 0
.PQ MOVEM &R, &X+&M
&M SET &M + 1
AIF (&M NE N) .PQ
MEND
MACRO CALL
TEST S,10
REPRESENTS PARAMETER NAME
REPRESENTS EXPAN. VAR. NAME
REPRESENTS SEQUENCING SYMBOL
NAME
REPRESENTS ACTUAL PARAMETER NAME

38. Advance directives
• The Remove Directive: Remove Macro from MDT(Macro definition table).
• The IRP Directive: (Indefinite repeat): It is used by programmer to direct
the assembler to repeatedly duplicate and assemble the sequence a
number of times determined by a compound parameter.
• IRP example
– Macro
– MAC_X &P, &Q
– IRP &P
– ADD REG1, &P
– IRP
– MEND
• MACRO CALL
– MAX_X (A ,B, #3), H
• On execution
– ADD REG1, A
– ADD REG1, B
– ADD REG1, #3

39. The REPEAT (REPT)Directive
• REPEAT: ): This is another facility with assembler to duplicate and
assemble the sequence a number of times during macro expansion.
• Syntax: REPT <expression>
– MACRO
– DEF_R
– LCL &P
– &P SET 5
– REPT 5
– DC ‘&P’
– &P SET &P+1
– ENDM
– MEND
– On execution
– 5,6,7,8,9,10 will be output

40. Design issues of Macro preocessor
• Flexible data structures and databases
• Attributes of macro arguments/parameter
name
• Default arguments/ formal parameter value at
macro definition time
• Numeric values of arguments/ actual
parameter value at macro call
• Comments in macros

41. Features of macro processor
• Associating macro parameters with their
arguments
• Delimiting macro parameters
• Directives related to arguments
• Automatic label generation
• Machine independent features

42. Design of Macro Preprocessor

43. Functions of Macro preprocessor
• Macro processor will perform the following
tasks-
– Identifies macro definitions and calls in the
program.
– Determines formal parameters and their values.
– Keeps track of the values of expansion time
variables and sequencing symbols declared in a
macro.
– Handles expansion time control flow and performs
expansion of model statements.

44. Two pass Macro Processor
• General Design Steps
• Step 1: Specification of Problem:-
• Step 2 Specification of databases:-
• Step 3 Specification of database
formats
• Step 4 : Algorithm

45. Specify the problem
• In Pass-I the macro definitions are searched
and stored in the macro definition table and
the entry is made in macro name table
• In Pass-II the macro calls are identified and the
arguments are placed in the appropriate place
and the macro calls are replaced by macro
definitions.

46. Specification of databases:-
Pass 1:-
• The input macro source program.
• The output macro source program to be used by Pass2.
• Macro-Definition Table (MDT), to store the body of macro
defns.
• Macro-Definition Table Counter (MDTC), to mark next
available entry MDT.
• Macro- Name Table (MNT), used to store names of macros.
• Macro Name Table counter (MNTC), used to indicate the
next available entry in MNT.
• Argument List Array (ALA), used to substitute index markers
for dummy arguments before storing a macro-defns.

47. Specification of databases:-
• Pass 2:-
• The copy of the input from Pass1.
• The output expanded source to be given to assembler.
• MDT, created by Pass1.
• MNT, created by Pass1.
• Macro-Definition Table Pointer (MDTP), used to
indicate the next line of text to be used during macro-
expansion.
• Argument List Array (ALA), used to substitute macro-
call arguments for the index markers in the stored
macro-defns

48. Specification of Database format

49. Specification of Database format

50. EXAMPLE
MACRO
TEST &X, &N, R=AREG
LCL &M
&M SET 0
.PQ MOVEM &R, &X+&M
&M SET &M + 1
AIF (&M NE N) .PQ
MEND
MACRO CALL
TEST S,10
REPRESENTS PARAMETER NAME
REPRESENTS EXPAN. VAR. NAME
REPRESENTS SEQUENCING SYMBOL
NAME
REPRESENTS ACTUAL PARAMETER NAME

51. X
N
R
PNTAB
M
EVNTAB
R AREG
KPDTAB
PQ
SSNTAB
S
10
AREG
APTAB
0
EVTAB
27
SSTAB

52. Name #PP #KP #EV MDTP KPDTP SSTP
TEST 2 1 1 25 10 5
MNT
25 LCL (E,1)
26 (E,1) SET 0
27 MOVEM (P,3),(P,1)+(E,1)
28 (E,1) SET (E,1) +1
29 AIF (E,1) NE (P,2) (S,1)
30 MEND
MDT

53. Steps for MNT Entry
Name #PP #KP #EV MDTP KPDTP SSTP
TEST &X, &N, R=AREG
STRUCTURE OF MNT
For each positional parameter
(i) Enter Parameter name in PNTAB [PNTAB_ptr]
(ii)PNTAB_ptr := PNTAB_Ptr + 1;
(iii)# PP := # PP + 1 :
PNTAB
x
#pp=1
N
#pp=1+1=2

54. .PQ MOVEM &R, &X+&M
SSNTAB
a) If SS is present in SSNTAB then get index No.
Else
1 Enter SS in SSNTAB, then get index No. and
2. Enter MDT_Ptr in SSTAB
b) For a parameter , generate the specification ( p,#n).
c) For an expansion variable,generate the
specification ( E, # m).
.PQ
SSTAB
5
27
.PQ MOVEM &R, &X+&M
MOVEM (P,3) , (P,1)+(E,1) Enter this line into MDT
Steps for Model Stmt

55. Argument List Array (ALA):
• ALA is used during both Pass1 & Pas2 but for some what
reverse functions.
• During Pass1, in order to simplify later argument
replacement during macro expansion, dummy arguments
are replaced with positional indicators when defn is stored.
Ex. # 1, # 2, # 3 etc.
• The ith dummy argument on the macro-name is
represented in the body by #i.
• These symbols are used in conjunction with ALA prepared
before expansion of a macro-call.
• Symbolic dummy argument are retained on macro-name to
enable the macro processor to handle argument
replacement byname rather by position.

56. During pass-I

57. Algorithm
• Pass1 of macro processor makes a line-by-line scan
over its input.
• Set MDTC = 1 as well as MNTC = 1.
• Read next line from input program.
• If it is a MACRO pseudo-op, the entire macro definition
except this (MACRO) line is stored in MDT.
• The name is entered into Macro Name Table along with
a pointer to the first location of MDT entry of the
definition.
• When the END pseudo-op is encountered all the
macro-defns have been processed, so control is
transferred to pass2

58. MDTC 1
MNTC 1
MDTC MDTC+1
MDTC MDTC+1
Enter Macro Name and Current
value of MDTC in MNT

59. Algorithm for Pass – 2
• This algorithm reads one line of i/p prog. at a time.
• for each Line it checks if op-code of that line matches any of the MNT
entry.
• When match is found (i.e. when call is pointer called MDTF to
corresponding macro defns stored in MDT.
• The initial value of MDTP is obtained from MDT index field of MNT
entry.
• The macro expander prepares the ALA consisting of a table of dummy
argument indices & corresponding arguments to the call.
• Reading proceeds from the MDT, as each successive line is read, The
values form the argument list one substituted for dummy arguments
indices in the macro defn.
• Reading MEND line in MDT terminates expansion of macro & scanning
continues from the input file.
• When END pseudo-op encountered , the expanded source program is
given to the assembler

60. MDTP  MDTP + 1

61. Pass structure of Macro assembler

62. Macro assembler flow chart