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Do a prefetch of 1 token

C is a LR(2) language so it means we need 2 tokens in order to
decide what is the next step. We have solving this problem with
backtracking and a tricky ahead, that was used only to detect that
the proximus token was ':' or not. Since we want to remove the
backtracking we need a real ahead() function, and the better
way is having a prefetch token.

--- a/lex.c

+++ b/lex.c

@@ -9,10 +9,9 @@

 #include "symbol.h"

 #include "sizes.h"

-#define NR_KEYW_HASH 16

-

 unsigned char yytoken;

 char yytext[IDENTSIZ + 1];

+static char yybuf[IDENTSIZ + 1];

 unsigned linenum;

 unsigned columnum;

 const char *filename;

@@ -24,7 +23,7 @@

 };

 static FILE *yyin;

-

+static struct symbol yysym = {.name = ""}, *yynval = &yysym;

 struct symbol *yyval;

 struct symbol *

@@ -50,6 +49,7 @@

 	v = strtoll(s, NULL, base);

 	sym = lookup(NULL, NS_IDEN);

+	sym->tok = CONSTANT;

 	sym->ctype = *tp;

 	switch (tp->type) {

@@ -72,7 +72,7 @@

 	return sym;

 }

-static char

+static struct symbol *

 number(void)

 {

 	register char *bp, ch;

@@ -90,7 +90,7 @@

 		ungetc(ch, yyin);

 	}

-	for (bp = yytext; bp < &yytext[IDENTSIZ]; *bp++ = ch) {

+	for (bp = yybuf; bp < &yybuf[IDENTSIZ]; *bp++ = ch) {

 		ch = getc(yyin);

 		switch (base) {

 		case 8:

@@ -108,13 +108,11 @@

 		}

 	}

-end:	if (bp == &yytext[IDENTSIZ])

-		error("identifier too long %s", yytext);

+end:	if (bp == &yybuf[IDENTSIZ])

+		error("identifier too long %s", yybuf);

 	*bp = '\0';

 	ungetc(ch, yyin);

-	yyval = integer(yytext, base);

-

-	return CONSTANT;

+	return integer(yybuf, base);

 }

 void

@@ -169,35 +167,36 @@

 	}

 }

-static unsigned char

+static struct symbol *

 iden(void)

 {

 	register char ch, *bp;

-	for (bp = yytext; bp < &yytext[IDENTSIZ]; *bp++ = ch) {

+	for (bp = yybuf; bp < &yybuf[IDENTSIZ]; *bp++ = ch) {

 		if (!isalnum(ch = getc(yyin)) && ch != '_')

 			break;

 	}

-	if (bp == &yytext[IDENTSIZ])

-		error("identifier too long %s", yytext);

+	if (bp == &yybuf[IDENTSIZ])

+		error("identifier too long %s", yybuf);

 	*bp = '\0';

 	ungetc(ch, yyin);

-	yyval = lookup(yytext, NS_IDEN);

-	return yyval->tok;

+	return lookup(yybuf, NS_IDEN);

 }

 static unsigned char

 skip(void)

 {

-	register int c;

+	static int c;

 	extern char parser_out_home;

-	while (isspace(c = getc(yyin))) {

-		switch (c) {

-		case '\n': ++linenum, columnum = 1; break;

-		case '\t': columnum += 8;	    break;

-		default:   ++columnum;		    break;

+	if (c != EOF) {

+		while (c != EOF && isspace(c = getc(yyin))) {

+			switch (c) {

+			case '\n': ++linenum, columnum = 1; break;

+			case '\t': columnum += 8;	    break;

+			default:   ++columnum;		    break;

+			}

 		}

 	}

 	if (c == EOF) {

@@ -214,14 +213,14 @@

 {

 	register char c = getc(yyin);

-	yytext[1] = c;

-	yytext[2] = '\0';

+	yybuf[1] = c;

+	yybuf[2] = '\0';

 	if (c == '=')

 		return eq;

 	else if (c == op && rep)

 		return rep;

-	yytext[1] = '\0';

+	yybuf[1] = '\0';

 	ungetc(c, yyin);

 	return op;

 }

@@ -231,23 +230,24 @@

 {

 	static char tokens[2][3] = {

 		{GE, SHL, SHL_EQ},

-		{LE, SHR, SHR_EQ}};

+		{LE, SHR, SHR_EQ}

+	};

 	register char c = getc(yyin);

 	register char *tp = tokens[op == '>'];

-	yytext[1] = c;

-	yytext[2] = '\0';

+	yybuf[1] = c;

+	yybuf[2] = '\0';

 	if (c == '=') {

 		return tp[0];

 	} else if (c == op) {

 		if ((c = getc(yyin)) == '=')  {

-			yytext[2] = c;

-			yytext[3] = '\0';

+			yybuf[2] = c;

+			yybuf[3] = '\0';

 			return tp[2];

 		}

 		op = tp[1];

 	} else {

-		yytext[1] = '\0';

+		yybuf[1] = '\0';

 	}

 	ungetc(c, yyin);

 	return op;

@@ -258,13 +258,13 @@

 {

 	register int c = getc(yyin);

-	yytext[1] = c;

+	yybuf[1] = c;

 	switch (c) {

 	case '-': return DEC;

 	case '>': return INDIR;

 	case '=': return SUB_EQ;

 	default:

-		yytext[1] = '\0';

+		yybuf[1] = '\0';

 		ungetc(c, yyin);

 		return '-';

 	}

@@ -275,8 +275,8 @@

 {

 	register unsigned char c = getc(yyin);

-	yytext[0] = c;

-	yytext[1] = '\0';

+	yybuf[0] = c;

+	yybuf[1] = '\0';

 	switch (c) {

 	case '=': return follow('=', EQ, 0);

 	case '^': return follow('^', XOR_EQ, 0);

@@ -297,16 +297,21 @@

 {

 	register unsigned char c;

+	strcpy(yytext, yybuf);

+	yyval = yynval;

+	yytoken = yynval->tok;

+	yynval = &yysym;

+

 	if (!skip()) {

-		yytoken = EOFTOK;

+		yysym.tok = EOFTOK;

 	} else {

 		ungetc(c = getc(yyin), yyin);

 		if (isalpha(c) || c == '_')

-			yytoken = iden();

+			yynval = iden();

 		else if (isdigit(c))

-			yytoken = number();

+			yynval = number();

 		else

-			yytoken = operator();

+			yysym.tok = operator();

 	}

 }

@@ -313,12 +318,7 @@

 unsigned char

 ahead(void)

 {

-	register char c;

-

-	if (!skip())

-		return EOFTOK;

-	ungetc(c = getc(yyin), yyin);

-	return c;

+	return yynval->tok;

 }

 char

@@ -347,10 +347,11 @@

 	if (file == NULL) {

 		yyin = stdin;

 		filename = "(stdin)";

-		return;

+	} else {

+		if ((yyin = fopen(file, "r")) == NULL)

+			die("file '%s' not found", file);

+		filename = file;

 	}

-	if ((yyin = fopen(file, "r")) == NULL)

-		die("file '%s' not found", file);

-	filename = file;

 	columnum = linenum = 1;

+	next();      /* prefetch first token */

 }