scan.c

Scanner

This is the lexical analysis stage (scanner) of the compiler. It turns the input program a stream of tokens, including their associated attributes (names, values, etc).

/*
 *	NMH's Simple C Compiler, 2011,2012,2022
 *	Lexical analysis (scanner)
 */

#include "defs.h"
#include "data.h"
#include "decl.h"

int next(void) {
	int	c;

	if (Putback) {
		c = Putback;
		Putback = 0;
		return c;
	}
	if (Mp) {
		if ('\0' == *Macp[Mp-1]) {
			Macp[Mp-1] = NULL;
			return Macc[--Mp];
		}
		else {
			return *Macp[Mp-1]++;
		}
	}
	c = fgetc(Infile);
	if ('\n' == c) Line++;
	return c;
}

void putback(int c) {
	Putback = c;
}

static int hexchar(void) {
	int	c, h, n = 0, f = 0;

	while (isxdigit(c = next())) {
		h = chrpos("0123456789abcdef", tolower(c));
		n = n * 16 + h;
		f = 1;
	}
	putback(c);
	if (!f)
		error("missing digits after '\\x'", NULL);
	if (n > 255)
		error("value out of range after '\\x'", NULL);
	return n;
}

static int scanch(void) {
	int	i, c, c2;

	c = next();
	if ('\\' == c) {
		switch (c = next()) {
		case 'a': return '\a';
		case 'b': return '\b';
		case 'f': return '\f';
		case 'n': return '\n';
		case 'r': return '\r';
		case 't': return '\t';
		case 'v': return '\v';
		case '\\': return '\\';
		case '"': return '"' | 256;
		case '\'': return '\'';
		case '0': case '1': case '2':
		case '3': case '4': case '5':
		case '6': case '7':
			for (c2 = i = 0; isdigit(c) && c < '8'; c = next()) {
				if (++i > 3) break;
				c2 = c2 * 8 + (c - '0');
			}
			putback(c);
			return c2;
		case 'x':
			return hexchar();
		default:
			cerror("unknown escape sequence: %s", c);
			return ' ';
		}
	}
	else {
		return c;
	}
}

static int scanint(int c) {
	int	val, radix, k, i = 0;

	val = 0;
	radix = 10;
	if ('0' == c) {
		Text[i++] = '0';
		if ((c = next()) == 'x') {
			radix = 16;
			Text[i++] = c;
			c = next();
		}
		else {
			radix = 8;
		}
	}
	while ((k = chrpos("0123456789abcdef", tolower(c))) >= 0) {
		Text[i++] = c;
		if (k >= radix)
			cerror("invalid digit in integer literal: %s", c);
		val = val * radix + k;
		c = next();
	}
	putback(c);
	Text[i] = 0;
	return val;
}

static int scanstr(char *buf) {
	int	i, c;

	buf[0] = '"';
	for (i=1; i<TEXTLEN-2; i++) {
		if ((c = scanch()) == '"') {
			buf[i++] = '"';
			buf[i] = 0;
			return Value = i;
		}
		buf[i] = c;
	}
	fatal("string literal too long");
	return 0;
}

static int scanident(int c, char *buf, int lim) {
	int	i = 0;

	while (isalpha(c) || isdigit(c) || '_' == c) {
		if (lim-1 == i) {
			error("identifier too long", NULL);
			i++;
		}
		else if (i < lim-1) {
			buf[i++] = c;
		}
		c = next();
	}
	putback(c);
	buf[i] = 0;
	return i;
}

int skip(void) {
	int	c, p, nl;

	c = next();
	nl = 0;
	for (;;) {
		if (EOF == c) {
			strcpy(Text, "<EOF>");
			return EOF;
		}
		while (' ' == c || '\t' == c || '\n' == c ||
			'\r' == c || '\f' == c
		) {
			if ('\n' == c) nl = 1;
			c = next();
		}
		if (nl && c == '#') {
			preproc();
			c = next();
			continue;
		}
		nl = 0;
		if (c != '/')
			break;
		if ((c = next()) != '*') {
			putback(c);
			c = '/';
			break;
		}
		p = 0;
		while ((c = next()) != EOF) {
			if ('/' == c && '*' == p) {
				c = next();
				break;
			}
			p = c;
		}
	}
	return c;
}

static int keyword(char *s) {
	switch (*s) {
	case '#':
		switch (s[1]) {
		case 'd':
			if (!strcmp(s, "#define")) return P_DEFINE;
			break;
		case 'e':
			if (!strcmp(s, "#else")) return P_ELSE;
			if (!strcmp(s, "#endif")) return P_ENDIF;
			break;
		case 'i':
			if (!strcmp(s, "#ifdef")) return P_IFDEF;
			if (!strcmp(s, "#ifndef")) return P_IFNDEF;
			if (!strcmp(s, "#include")) return P_INCLUDE;
			break;
		case 'u':
			if (!strcmp(s, "#undef")) return P_UNDEF;
			break;
		}
		break;
	case 'b':
		if (!strcmp(s, "break")) return BREAK;
		break;
	case 'c':
		if (!strcmp(s, "case")) return CASE;
		if (!strcmp(s, "char")) return CHAR;
		if (!strcmp(s, "continue")) return CONTINUE;
		break;
	case 'd':
		if (!strcmp(s, "default")) return DEFAULT;
		if (!strcmp(s, "do")) return DO;
		break;
	case 'e':
		if (!strcmp(s, "else")) return ELSE;
		if (!strcmp(s, "enum")) return ENUM;
		if (!strcmp(s, "extern")) return EXTERN;
		break;
	case 'f':
		if (!strcmp(s, "for")) return FOR;
		break;
	case 'i':
		if (!strcmp(s, "if")) return IF;
		if (!strcmp(s, "int")) return INT;
		break;
	case 'r':
		if (!strcmp(s, "return")) return RETURN;
		break;
	case 's':
		if (!strcmp(s, "sizeof")) return SIZEOF;
		if (!strcmp(s, "static")) return STATIC;
		if (!strcmp(s, "switch")) return SWITCH;
		break;
	case 'v':
		if (!strcmp(s, "void")) return VOID;
		break;
	case 'w':
		if (!strcmp(s, "while")) return WHILE;
		break;
	case '_':
		if (!strcmp(s, "__argc")) return __ARGC;
		break;
	}
	return 0;
}

static int macro(char *name) {
	int	y;

	y = findmac(name);
	if (!y || Types[y] != TMACRO)
		return 0;
	playmac(Mtext[y]);
	return 1;
}

static int scanpp(void) {
	int	i, c, t;

	if (Rejected != -1) {
		t = Rejected;
		Rejected = -1;
		strcpy(Text, Rejtext);
		Value = Rejval;
		return t;
	}
	for (;;) {
		Value = 0;
		c = skip();
		memset(Text, 0, 4);
		Text[0] = c;
		switch (c) {
		case '!':
			if ((c = next()) == '=') {
				Text[1] = '=';
				return NOTEQ;
			}
			else {
				putback(c);
				return XMARK;
			}
		case '%':
			if ((c = next()) == '=') {
				Text[1] = '=';
				return ASMOD;
			}
			else {
				putback(c);
				return MOD;
			}
		case '&':
			if ((c = next()) == '&') {
				Text[1] = '&';
				return LOGAND;
			}
			else if ('=' == c) {
				Text[1] = '=';
				return ASAND;
			}
			else {
				putback(c);
				return AMPER;
			}
		case '(':
			return LPAREN;
		case ')':
			return RPAREN;
		case '*':
			if ((c = next()) == '=') {
				Text[1] = '=';
				return ASMUL;
			}
			else {
				putback(c);
				return STAR;
			}
		case '+':
			if ((c = next()) == '+') {
				Text[1] = '+';
				return INCR;
			}
			else if ('=' == c) {
				Text[1] = '=';
				return ASPLUS;
			}
			else {
				putback(c);
				return PLUS;
			}
		case ',':
			return COMMA;
		case '-':
			if ((c = next()) == '-') {
				Text[1] = '-';
				return DECR;
			}
			else if ('=' == c) {
				Text[1] = '=';
				return ASMINUS;
			}
			else {
				putback(c);
				return MINUS;
			}
		case '/':
			if ((c = next()) == '=') {
				Text[1] = '=';
				return ASDIV;
			}
			else {
				putback(c);
				return SLASH;
			}
		case ':':
			return COLON;
		case ';':
			return SEMI;
		case '<':
			if ((c = next()) == '<') {
				Text[1] = '<';
				if ((c = next()) == '=') {
					Text[2] = '=';
					return ASLSHIFT;
				}
				else {
					putback(c);
					return LSHIFT;
				}
			}
			else if ('=' == c) {
				Text[1] = '=';
				return LTEQ;
			}
			else {
				putback(c);
				return LESS;
			}
		case '=':
			if ((c = next()) == '=') {
				Text[1] = '=';
				return EQUAL;
			}
			else {
				putback(c);
				return ASSIGN;
			}
		case '>':
			if ((c = next()) == '>') {
				Text[1] = '>';
				if ((c = next()) == '=') {
					Text[1] = '=';
					return ASRSHIFT;
				}
				else {
					putback(c);
					return RSHIFT;
				}
			}
			else if ('=' == c) {
				Text[1] = '=';
				return GTEQ;
			}
			else {
				putback(c);
				return GREATER;
			}
		case '?':
			return QMARK;
		case '[':
			return LBRACK;
		case ']':
			return RBRACK;
		case '^':
			if ((c = next()) == '=') {
				Text[1] = '=';
				return ASXOR;
			}
			else {
				putback(c);
				return CARET;
			}
		case '{':
			return LBRACE;
		case '|':
			if ((c = next()) == '|') {
				Text[1] = '|';
				return LOGOR;
			}
			else if ('=' == c) {
				Text[1] = '=';
				return ASOR;
			}
			else {
				putback(c);
				return PIPE;
			}
		case '}':
			return RBRACE;
		case '~':
			return TILDE;
		case EOF:
			strcpy(Text, "<EOF>");
			return XEOF;
		case '\'':
			Text[1] = Value = scanch();
			if ((c = next()) != '\'')
				error(
				 "expected '\\'' at end of char literal",
					NULL);
			Text[2] = '\'';
			return INTLIT;
		case '"':
			Value = scanstr(Text);
			return STRLIT;
		case '#':
			Text[0] = '#';
			scanident(next(), &Text[1], TEXTLEN-1);
			if ((t = keyword(Text)) != 0)
				return t;
			error("unknown preprocessor command: %s", Text);
			return IDENT;
		case '.':
			for (i=1; i<3; i++)
				Text[i] = next();
			Text[i] = 0;
			if (strcmp(Text, "..."))
				error("malformed ellipsis: '%s'", Text);
			return ELLIPSIS;
		default:
			if (isdigit(c)) {
				Value = scanint(c);
				return INTLIT;
			}
			else if (isalpha(c) || '_' == c) {
				Value = scanident(c, Text, TEXTLEN);
				if (Expandmac && macro(Text))
					break;
				if ((t = keyword(Text)) != 0)
					return t;
				return IDENT;
			}
			else {
				cerror("funny input character: %s", c);
				break;
			}
		}
	}
}

int scan(void) {
	int	t;

	do {
		t = scanpp();
		if (!Inclev && Isp && XEOF == t)
			fatal("missing #endif at EOF");
	} while (frozen(1));
	if (t == Syntoken)
		Syntoken = 0;
	return t;
}

int scanraw(void) {
	int	t, oisp;

	oisp = Isp;
	Isp = 0;
	Expandmac = 0;
	t = scan();
	Expandmac = 1;
	Isp = oisp;
	return t;
}

void reject(void) {
	Rejected = Token;
	Rejval = Value;
	strcpy(Rejtext, Text);
}

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