Implementation of simple macro using C - programming language

1. System Programming Sunita M. Dol, CSE Dept
Walchand Institute of Technology, Solapur Page 1
HANDOUT#04
Aim:
Implementation of simple macro
Theory:
A macro is a unit of specification for program generation through expansion.
Macro Definition
A macro definition is enclosed between a macro header statement and a macro end
statement. Macro definitions are typically located at the start of a program. Macro
definition consists of:
1. Macro prototype statements
2. One or more model statements
3. Macro preprocessor statements
1. Macro prototype statements.
The macro prototype statement declares the name of the macro and the names and
kinds of its parameters. The macro prototype statement has the following syntax:
<macro name> [<formal parameter specification>[ …..]]
where <macro name> appears in the mnemonic field of assembly Statement and
<formal parameter specification> is of the form
&<parameter name> [<parameter kind>]
2. Model statements.
A model statement is a statement from which assembly language statements may
be generated during macro expansion.
3. Macro preprocessor statements.
A preprocessor statement is used to perform auxiliary functions during macro
expansion.

2. System Programming Sunita M. Dol, CSE Dept
Walchand Institute of Technology, Solapur Page 2
Macro call
A macro is called by writing the macro name in the mnemonic field of an
assembly statement. The macro call has syntax
<macro name> [<actual parameter specification>[,….]]
where actual parameter resembles an operand specification in assembly statement.
Example
The definition of macro INCR is given below
MACRO
INCR &MEM_VAL, &INCR_VAL, &REG
MOVER &REG, &MEM_VAL
ADD &REG, &INCR-VAL
MOVEM &REG, &MEM_VAL
MEND
Macro Expansion
A macro leads to macro expansion. During macro expansion, the use of a macro
name with a set of actual parameters i.e. the macro call statement is replaced by a
sequence of assembly code. To differentiate between the original statement of a
program and the statements resulting from macro expansion, each expanded
statement is marked with a ‘+’ preceding its label field.
There are two kinds of expansions
1. Lexical expansion.
2. Semantic expansion
1. Lexical expansion.
Lexical expansion implies replacement of a character string by another character
string during program generation. It replaces the occurrences of formal parameter
by corresponding actual parameters.
Example
Consider the following macro definition
MACRO
INCR &MEM_VAL, &INCR_VAL, &REG
MOVER &REG, &MEM_VAL
ADD &REG, &INCR-VAL
MOVEM &REG, &MEM_VAL

3. System Programming Sunita M. Dol, CSE Dept
Walchand Institute of Technology, Solapur Page 3
MEND
Consider macro call statement on INCR
INCR A, B, AREG
The values of formal parameters are:
Formal parameter value
MEM_VAL A
INCR_VAL B
REG AREG
Lexical expansion of the model statement leads to the code
+ MOVER AREG, A
+ ADD AREG, B
+ MOVEM AREG, A
2. Semantic expansion
Semantic expansion implies generation of instructions tailored to the requirements
of a specific usage e.g. generation of type specific instruction for manipulation of
byte and word operands. It is characterized by the fact that different use of macro
can lead to codes which differ in the number, sequence and opcodes of
instructions.
Example
Consider the macro definition
MACRO
CLEAR &X, &N
LCL &M
&M SET 0
MOVER AREG, =’0’
.MORE MOVEM AREG, &X+&M
&M SET &M+1
AIF (&M NE N) .MORE
MEND
Consider the macro call CLEAR B, 3

4. System Programming Sunita M. Dol, CSE Dept
Walchand Institute of Technology, Solapur Page 4
This macro call leads to generation of statements:
+ MOVER AREG, =’0’
+ MOVEM AREG, B
+ MOVEM AREG, B+1
+ MOVEM AREG, B+2
Input:
#include<stdio.h>
#define xyz 5
#define asd 10
#define pf printf
#define sf scanf
void main(void)
{
pf("Enter a no:");
sf("%d",&a);
b=asd+xyz;
pf("xyz=%d",b);
}
Output:
The old program
#include<stdio.h>
#define xyz 5
#define asd 10
#define pf printf
#define sf scanf
void main(void)
{

5. System Programming Sunita M. Dol, CSE Dept
Walchand Institute of Technology, Solapur Page 5
pf("Enter a no:");
sf("%d",&a);
b=asd+xyz;
pf("xyz=%d",b);
}
Macro Expansion
xyz 5
asd 10
pf printf
sf scanf
The new program
#include<stdio.h>
void main(void)
{
printf("Enter a no:");
scanf("%d",&a);
b=10+5;
printf("xyz=%d",b);
}
Conclusion:
A macro is a unit of specification for program generation through expansion. A
simple macro is implemented in C-language