1. Algorithm for One-pass Macro Processor
main () /* main program */ {
EXPANDING = 0; /* definition case; a control variable for reading input record from input sources */
while (OPCODE != ‘END’) {
GETLINE (line); /* get a next line (from expansion or definition); label, opcode, operands */
PROCESSLINE (line); /* define or expand a line after getting it; label, opcode, operands*/ }
PROCESSLINE (line)
search NAMTAB for line.opcode;
if (found)
EXPAND (line); /* expand macro definition with arguments from invocation */
else if
DEFINE (line); /* put macro definition in DEFTAB */
else
write the source line to expand file;
CmpE Software Systems
Prof. Weider Yu

2. Algorithm for One-pass Macro Processor
DEFINE (line) {
enter line.label into NAMTAB; /* enter macro name into NAMTAB */
enter macro prototype into DEFTAB; /* the first declaration statement */
LEVEL = 1;
while (LEVEL > 0) {
GETLINE (line); /* get the next line of the macro definition */
if (line != comment line) {
substitute positional notation for parameters; /* &param_1  ?1, etc. */
enter line into DEFTAB;
if (OPCODE = ‘MACRO’)
LEVEL = LEVEL +1;
else if (OPCODE = ‘MEND’)
LEVEL = LEVEL –1; }
store pointers (label->begin and label->end) in NAMTAB; /* store macro def. begin and end pointers */
CmpE Software Systems
Prof. Weider Yu

3. Algorithm for One-pass Macro Processor
EXPAND (line) {
EXPANDING = 1; /* expansion case; ready to read input from DEFTAB*/
get the first line of macro definition (macro prototype) from DEFTAB;
set up arguments (from macro invocation) in ARGTAB;
write macro invocation to expanded file (output file) as a comment;
while (OPCODE != MEND) { /* while not end of macro definition */
GETLINE (line);
PROCESSLINE (line); }
EXPANDING = 0; /* macro expansion is done */
GETLINE (line)
if (EXPANDING = 1) {
get next line of macro definition from DEFTAB;
substitute arguments from ARGTAB for position notation;
else
read next line from input file; /* read the source program file */
CmpE Software Systems
Prof. Weider Yu

4. One-pass Macro Processor Algorithm
A flow chart for the one-pass macro processor algorithm. 2
INPUT FILE
READ (next line) 2 1
GETLINE
READ (next line)
MACRO
PROCESSOR
DEFTAB 5
SUBSTITUTE (arguments) 4
PROCESSLINE
DEFINE
ENTER (macro prototype/line)
WRITE (source line) 3 5
EXPANDED FILE
SEARCH 5
EXPAND
ARGTAB
NAMTAB
ENTER (macro name)
SET UP (arguments)
CmpE Software Systems
Prof. Weider Yu