pl0.c

plo 清华版的第二章的那个！！ 1． 基本内容（成绩范围：“中”、“及格”或“不及格”） 对PL/0作以下修改扩充： （1）增加单词：保留字 ELSE

} // condition

//////////////////////////////////////////////////////////////////////
void statement(symset fsys)
{
	int i, cx1, cx2;
	symset set1, set;

	if (sym == SYM_IDENTIFIER)
	{ // variable assignment
		mask* mk;
		if (! (i = position(id)))
		{
			error(11); // Undeclared identifier.
		}
		else if (table[i].kind != ID_VARIABLE)
		{
			error(12); // Illegal assignment.
			i = 0;
		}
		getsym();
		if (sym == SYM_BECOMES)
		{
			getsym();
		}
		else
		{
			error(13); // ':=' expected.
		}
		expression(fsys);
		mk = (mask*) &table[i];
		if (i)
		{
			gen(STO, level - mk->level, mk->address);
		}
	}
	else if (sym == SYM_CALL)
	{ // procedure call
		getsym();
		if (sym != SYM_IDENTIFIER)
		{
			error(14); // There must be an identifier to follow the 'call'.
		}
		else
		{
			if (! (i = position(id)))
			{
				error(11); // Undeclared identifier.
			}
			else if (table[i].kind == ID_PROCEDURE)
			{
				mask* mk;
				mk = (mask*) &table[i];
				gen(CAL, level - mk->level, mk->address);
			}
			else
			{
				error(15); // A constant or variable can not be called. 
			}
			getsym();
		}
	} 
	else if (sym == SYM_IF)
	{ // if statement
		getsym();
		set1 = createset(SYM_THEN, SYM_DO, SYM_NULL);
		set = uniteset(set1, fsys);
		condition(set);
		destroyset(set1);
		destroyset(set);
		if (sym == SYM_THEN)
		{
			getsym();
		}
		else
		{
			error(16); // 'then' expected.
		}
		cx1 = cx;
		gen(JPC, 0, 0);
		statement(fsys);
		code[cx1].a = cx;	
	}
	else if (sym == SYM_BEGIN)
	{ // block
		getsym();
		set1 = createset(SYM_SEMICOLON, SYM_END, SYM_NULL);
		set = uniteset(set1, fsys);
		statement(set);
		while (sym == SYM_SEMICOLON || inset(sym, statbegsys))
		{
			if (sym == SYM_SEMICOLON)
			{
				getsym();
			}
			else
			{
				error(10);
			}
			statement(set);
		} // while
		destroyset(set1);
		destroyset(set);
		if (sym == SYM_END)
		{
			getsym();
		}
		else
		{
			error(17); // ';' or 'end' expected.
		}
	}
	else if (sym == SYM_WHILE)
	{ // while statement
		cx1 = cx;
		getsym();
		set1 = createset(SYM_DO, SYM_NULL);
		set = uniteset(set1, fsys);
		condition(set);
		destroyset(set1);
		destroyset(set);
		cx2 = cx;
		gen(JPC, 0, 0);
		if (sym == SYM_DO)
		{
			getsym();
		}
		else
		{
			error(18); // 'do' expected.
		}
		statement(fsys);
		gen(JMP, 0, cx1);
		code[cx2].a = cx;
	}
	test(fsys, phi, 19);
} // statement
			
//////////////////////////////////////////////////////////////////////
void block(symset fsys)
{
	int cx0; // initial code index
	mask* mk;
	int block_dx;
	int savedTx;
	symset set1, set;

	dx = 3;
	block_dx = dx;
	mk = (mask*) &table[tx];
	mk->address = cx;
	gen(JMP, 0, 0);
	if (level > MAXLEVEL)
	{
		error(32); // There are too many levels.
	}
	do
	{
		if (sym == SYM_CONST)
		{ // constant declarations
			getsym();
			do
			{
				constdeclaration();
				while (sym == SYM_COMMA)
				{
					getsym();
					constdeclaration();
				}
				if (sym == SYM_SEMICOLON)
				{
					getsym();
				}
				else
				{
					error(5); // Missing ',' or ';'.
				}
			}
			while (sym == SYM_IDENTIFIER);
		} // if

		if (sym == SYM_VAR)
		{ // variable declarations
			getsym();
			do
			{
				vardeclaration();
				while (sym == SYM_COMMA)
				{
					getsym();
					vardeclaration();
				}
				if (sym == SYM_SEMICOLON)
				{
					getsym();
				}
				else
				{
					error(5); // Missing ',' or ';'.
				}
			}
			while (sym == SYM_IDENTIFIER);
//			block = dx;
		} // if

		while (sym == SYM_PROCEDURE)
		{ // procedure declarations
			getsym();
			if (sym == SYM_IDENTIFIER)
			{
				enter(ID_PROCEDURE);
				getsym();
			}
			else
			{
				error(4); // There must be an identifier to follow 'const', 'var', or 'procedure'.
			}


			if (sym == SYM_SEMICOLON)
			{
				getsym();
			}
			else
			{
				error(5); // Missing ',' or ';'.
			}

			level++;
			savedTx = tx;
			set1 = createset(SYM_SEMICOLON, SYM_NULL);
			set = uniteset(set1, fsys);
			block(set);
			destroyset(set1);
			destroyset(set);
			tx = savedTx;
			level--;

			if (sym == SYM_SEMICOLON)
			{
				getsym();
				set1 = createset(SYM_IDENTIFIER, SYM_PROCEDURE, SYM_NULL);
				set = uniteset(statbegsys, set1);
				test(set, fsys, 6);
				destroyset(set1);
				destroyset(set);
			}
			else
			{
				error(5); // Missing ',' or ';'.
			}
		} // while
		set1 = createset(SYM_IDENTIFIER, SYM_NULL);
		set = uniteset(statbegsys, set1);
		test(set, declbegsys, 7);
		destroyset(set1);
		destroyset(set);
	}
	while (inset(sym, declbegsys));

	code[mk->address].a = cx;
	mk->address = cx;
	cx0 = cx;
	gen(INT, 0, block_dx);
	set1 = createset(SYM_SEMICOLON, SYM_END, SYM_NULL);
	set = uniteset(set1, fsys);
	statement(set);
	destroyset(set1);
	destroyset(set);
	gen(OPR, 0, OPR_RET); // return
	test(fsys, phi, 8); // test for error: Follow the statement is an incorrect symbol.
	listcode(cx0, cx);
} // block

//////////////////////////////////////////////////////////////////////
int base(int stack[], int currentLevel, int levelDiff)
{
	int b = currentLevel;
	
	while (levelDiff--)
		b = stack[b];
	return b;
} // base

//////////////////////////////////////////////////////////////////////
// interprets and executes codes.
void interpret()
{
	int pc;        // program counter
	int stack[STACKSIZE];
	int top;       // top of stack
	int b;         // program, base, and top-stack register
	instruction i; // instruction register

	printf("Begin executing PL/0 program.\n");

	pc = 0;
	b = 1;
	top = 3;
	stack[1] = stack[2] = stack[3] = 0;
	do
	{
		i = code[pc++];
		switch (i.f)
		{
		case LIT:
			stack[++top] = i.a;
			break;
		case OPR:
			switch (i.a) // operator
			{
			case OPR_RET:
				top = b - 1;
				pc = stack[top + 3];
				b = stack[top + 2];
				break;
			case OPR_NEG:
				stack[top] = -stack[top];
				break;
			case OPR_ADD:
				top--;
				stack[top] += stack[top + 1];
				break;
			case OPR_MIN:
				top--;
				stack[top] -= stack[top + 1];
				break;
			case OPR_MUL:
				top--;
				stack[top] *= stack[top + 1];
				break;
			case OPR_DIV:
				top--;
				if (stack[top + 1] == 0)
				{
					fprintf(stderr, "Runtime Error: Divided by zero.\n");
					fprintf(stderr, "Program terminated.\n");
					continue;
				}
				stack[top] /= stack[top + 1];
				break;
			case OPR_ODD:
				stack[top] %= 2;
				break;
			case OPR_EQU:
				top--;
				stack[top] = stack[top] == stack[top + 1];
				break;
			case OPR_NEQ:
				top--;
				stack[top] = stack[top] != stack[top + 1];
			case OPR_LES:
				top--;
				stack[top] = stack[top] < stack[top + 1];
				break;
			case OPR_GEQ:
				top--;
				stack[top] = stack[top] >= stack[top + 1];
			case OPR_GTR:
				top--;
				stack[top] = stack[top] > stack[top + 1];
				break;
			case OPR_LEQ:
				top--;
				stack[top] = stack[top] <= stack[top + 1];
			} // switch
			break;
		case LOD:
			stack[++top] = stack[base(stack, b, i.l) + i.a];
			break;
		case STO:
			stack[base(stack, b, i.l) + i.a] = stack[top];
			printf("%d\n", stack[top]);
			top--;
			break;
		case CAL:
			stack[top + 1] = base(stack, b, i.l);
			// generate new block mark
			stack[top + 2] = b;
			stack[top + 3] = pc;
			b = top + 1;
			pc = i.a;
			break;
		case INT:
			top += i.a;
			break;
		case JMP:
			pc = i.a;
			break;
		case JPC:
			if (stack[top] == 0)
				pc = i.a;
			top--;
			break;
		} // switch
	}
	while (pc);

	printf("End executing PL/0 program.\n");
} // interpret

//////////////////////////////////////////////////////////////////////
void main ()
{
	FILE* hbin;
	char s[80];
	int i;
	symset set, set1, set2;

	printf("Please input source file name: "); // get file name to be compiled
	scanf("%s", s);
	if ((infile = fopen(s, "r")) == NULL)
	{
		printf("File %s can't be opened.\n", s);
		exit(1);
	}

	phi = createset(SYM_NULL);
	relset = createset(SYM_EQU, SYM_NEQ, SYM_LES, SYM_LEQ, SYM_GTR, SYM_GEQ, SYM_NULL);
	
	// create begin symbol sets
	declbegsys = createset(SYM_CONST, SYM_VAR, SYM_PROCEDURE, SYM_NULL);
	statbegsys = createset(SYM_BEGIN, SYM_CALL, SYM_IF, SYM_WHILE, SYM_NULL);
	facbegsys = createset(SYM_IDENTIFIER, SYM_NUMBER, SYM_LPAREN, SYM_NULL);

	err = cc = cx = ll = 0; // initialize global variables
	ch = ' ';
	kk = MAXIDLEN;

	getsym();

	set1 = createset(SYM_PERIOD, SYM_NULL);
	set2 = uniteset(declbegsys, statbegsys);
	set = uniteset(set1, set2);
	block(set);
	destroyset(set1);
	destroyset(set2);
	destroyset(set);
	destroyset(phi);
	destroyset(relset);
	destroyset(declbegsys);
	destroyset(statbegsys);
	destroyset(facbegsys);

	if (sym != SYM_PERIOD)
		error(9); // '.' expected.
	if (err == 0)
	{
		hbin = fopen("hbin.txt", "w");
		for (i = 0; i < cx; i++)
			fwrite(&code[i], sizeof(instruction), 1, hbin);
		fclose(hbin);
	}
	if (err == 0)
		interpret();
	else
		printf("There are %d error(s) in PL/0 program.\n", err);
	listcode(0, cx);
} // main

//////////////////////////////////////////////////////////////////////
// eof pl0.c