📄 pl0.c
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// pl0 compiler source code
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "pl0.h"
#include "set.c"
//////////////////////////////////////////////////////////////////////
// print error message.
void error(int n)
{
int i;
printf(" ");
for (i = 1; i <= cc - 1; i++)
printf(" ");
printf("^\n");
printf("Error %3d: %s\n", n, err_msg[n]);
err++;
} // error
//////////////////////////////////////////////////////////////////////
void getch(void)
{
if (cc == ll)
{
if (feof(infile))
{
printf("\nPROGRAM INCOMPLETE\n");
exit(1);
}
ll = cc = 0;
printf("%5d ", cx);
while ( (!feof(infile)) // added & modified by alex 01-02-09
&& ((ch = getc(infile)) != '\n'))
{
printf("%c", ch);
line[++ll] = ch;
} // while
printf("\n");
line[++ll] = ' ';
}
ch = line[++cc];
} // getch
//////////////////////////////////////////////////////////////////////
// gets a symbol from input stream.
void getsym(void)
{
int i, k;
char a[MAXIDLEN + 1];
while (ch == ' ')
getch();
if (isalpha(ch))
{ // symbol is a reserved word or an identifier.
k = 0;
do
{
if (k < MAXIDLEN)
a[k++] = ch;
getch();
}
while (isalpha(ch) || isdigit(ch));
a[k] = 0;
strcpy(id, a);
word[0] = id;
i = NRW;
while (strcmp(id, word[i--]));
if (++i)
sym = wsym[i]; // symbol is a reserved word
else
sym = SYM_IDENTIFIER; // symbol is an identifier
}
else if (isdigit(ch))
{ // symbol is a number.
k = num = 0;
sym = SYM_NUMBER;
do
{
num = num * 10 + ch - '0';
k++;
getch();
}
while (isdigit(ch));
if (k > MAXNUMLEN)
error(25); // The number is too great.
}
else if (ch == ':')
{
getch();
if (ch == '=')
{
sym = SYM_BECOMES; // :=
getch();
}
else
{
sym = SYM_NULL; // illegal?
}
}
else if (ch == '>')
{
getch();
if (ch == '=')
{
sym = SYM_GEQ; // >=
getch();
}
else
{
sym = SYM_GTR; // >
}
}
else if (ch == '<')
{
getch();
if (ch == '=')
{
sym = SYM_LEQ; // <=
getch();
}
else if (ch == '>')
{
sym = SYM_NEQ; // <>
getch();
}
else
{
sym = SYM_LES; // <
}
}
else
{ // other tokens
i = NSYM;
csym[0] = ch;
while (csym[i--] != ch);
if (++i)
{
sym = ssym[i];
getch();
}
else
{
printf("Fatal Error: Unknown character.\n");
exit(1);
}
}
} // getsym
//////////////////////////////////////////////////////////////////////
// generates (assembles) an instruction.
void gen(int x, int y, int z)
{
if (cx > CXMAX)
{
printf("Fatal Error: Program too long.\n");
exit(1);
}
code[cx].f = x;
code[cx].l = y;
code[cx++].a = z;
} // gen
//////////////////////////////////////////////////////////////////////
// tests if error occurs and skips all symbols that do not belongs to s1 or s2.
void test(symset s1, symset s2, int n)
{
symset s;
if (! inset(sym, s1))
{
error(n);
s = uniteset(s1, s2);
while(! inset(sym, s))
getsym();
destroyset(s);
}
} // test
//////////////////////////////////////////////////////////////////////
int dx; // data allocation index
// enter object(constant, variable or procedre) into table.
void enter(int kind)
{
mask* mk;
tx++;
strcpy(table[tx].name, id);
table[tx].kind = kind;
switch (kind)
{
case ID_CONSTANT:
if (num > MAXADDRESS)
{
error(25); // The number is too great.
num = 0;
}
table[tx].value = num;
break;
case ID_VARIABLE:
mk = (mask*) &table[tx];
mk->level = level;
mk->address = dx++;
break;
case ID_PROCEDURE:
mk = (mask*) &table[tx];
mk->level = level;
break;
} // switch
} // enter
//////////////////////////////////////////////////////////////////////
// locates identifier in symbol table.
int position(char* id)
{
int i;
strcpy(table[0].name, id);
i = tx + 1;
while (strcmp(table[--i].name, id) != 0);
return i;
} // position
//////////////////////////////////////////////////////////////////////
void constdeclaration()
{
if (sym == SYM_IDENTIFIER)
{
getsym();
if (sym == SYM_EQU || sym == SYM_BECOMES)
{
if (sym == SYM_BECOMES)
error(1); // Found ':=' when expecting '='.
getsym();
if (sym == SYM_NUMBER)
{
enter(ID_CONSTANT);
getsym();
}
else
{
error(2); // There must be a number to follow '='.
}
}
else
{
error(3); // There must be an '=' to follow the identifier.
}
} else error(4);
// There must be an identifier to follow 'const', 'var', or 'procedure'.
} // constdeclaration
//////////////////////////////////////////////////////////////////////
void vardeclaration(void)
{
if (sym == SYM_IDENTIFIER)
{
enter(ID_VARIABLE);
getsym();
}
else
{
error(4); // There must be an identifier to follow 'const', 'var', or 'procedure'.
}
} // vardeclaration
//////////////////////////////////////////////////////////////////////
void listcode(int from, int to)
{
int i;
printf("\n");
for (i = from; i < to; i++)
{
printf("%5d %s\t%d\t%d\n", i, mnemonic[code[i].f], code[i].l, code[i].a);
}
printf("\n");
} // listcode
//////////////////////////////////////////////////////////////////////
void factor(symset fsys)
{
void expression(symset fsys);
int i;
symset set;
test(facbegsys, fsys, 24); // The symbol can not be as the beginning of an expression.
while (inset(sym, facbegsys))
{
if (sym == SYM_IDENTIFIER)
{
if ((i = position(id)) == 0)
{
error(11); // Undeclared identifier.
}
else
{
switch (table[i].kind)
{
mask* mk;
case ID_CONSTANT:
gen(LIT, 0, table[i].value);
break;
case ID_VARIABLE:
mk = (mask*) &table[i];
gen(LOD, level - mk->level, mk->address);
break;
case ID_PROCEDURE:
error(21); // Procedure identifier can not be in an expression.
break;
} // switch
}
getsym();
}
else if (sym == SYM_NUMBER)
{
if (num > MAXADDRESS)
{
error(25); // The number is too great.
num = 0;
}
gen(LIT, 0, num);
getsym();
}
else if (sym == SYM_LPAREN)
{
getsym();
set = uniteset(createset(SYM_RPAREN, SYM_NULL), fsys);
expression(set);
destroyset(set);
if (sym == SYM_RPAREN)
{
getsym();
}
else
{
error(22); // Missing ')'.
}
}
test(fsys, createset(SYM_LPAREN, SYM_NULL), 23);
} // while
} // factor
//////////////////////////////////////////////////////////////////////
void term(symset fsys)
{
int mulop;
symset set;
set = uniteset(fsys, createset(SYM_TIMES, SYM_SLASH, SYM_NULL));
factor(set);
while (sym == SYM_TIMES || sym == SYM_SLASH)
{
mulop = sym;
getsym();
factor(set);
if (mulop == SYM_TIMES)
{
gen(OPR, 0, OPR_MUL);
}
else
{
gen(OPR, 0, OPR_DIV);
}
} // while
destroyset(set);
} // term
//////////////////////////////////////////////////////////////////////
void expression(symset fsys)
{
int addop;
symset set;
set = uniteset(fsys, createset(SYM_PLUS, SYM_MINUS, SYM_NULL));
if (sym == SYM_PLUS || sym == SYM_MINUS)
{
addop = sym;
getsym();
term(set);
if (addop == SYM_MINUS)
{
gen(OPR, 0, OPR_NEG);
}
}
else
{
term(set);
}
while (sym == SYM_PLUS || sym == SYM_MINUS)
{
addop = sym;
getsym();
term(set);
if (addop == SYM_PLUS)
{
gen(OPR, 0, OPR_ADD);
}
else
{
gen(OPR, 0, OPR_MIN);
}
} // while
destroyset(set);
} // expression
//////////////////////////////////////////////////////////////////////
void condition(symset fsys)
{
int relop;
symset set;
if (sym == SYM_ODD)
{
getsym();
expression(fsys);
gen(OPR, 0, 6);
}
else
{
set = uniteset(relset, fsys);
expression(set);
destroyset(set);
if (! inset(sym, relset))
{
error(20);
}
else
{
relop = sym;
getsym();
expression(fsys);
switch (relop)
{
case SYM_EQU:
gen(OPR, 0, OPR_EQU);
break;
case SYM_NEQ:
gen(OPR, 0, OPR_NEQ);
break;
case SYM_LES:
gen(OPR, 0, OPR_LES);
break;
case SYM_GEQ:
gen(OPR, 0, OPR_GEQ);
break;
case SYM_GTR:
gen(OPR, 0, OPR_GTR);
break;
case SYM_LEQ:
gen(OPR, 0, OPR_LEQ);
break;
} // switch
} // else
} // else
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