ncform

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#pragma lib	"libl.a"
int yylineno =1;
# define YYU(x) x
char yytext[YYLMAX];
struct yysvf *yylstate [YYLMAX], **yylsp, **yyolsp;
Uchar yysbuf[YYLMAX];
Uchar *yysptr = yysbuf;
int *yyfnd;
extern struct yysvf *yyestate;
int yyprevious = YYNEWLINE;
# ifdef LEXDEBUG
extern void allprint(int);
# endif
yylook(void){
	struct yysvf *yystate, **lsp;
	struct yywork *yyt;
	struct yysvf *yyz;
	int yych;
	struct yywork *yyr;
# ifdef LEXDEBUG
	int debug;
# endif
	Uchar *yylastch;
	/* start off machines */
# ifdef LEXDEBUG
	debug = 0;
# endif
	if (!yymorfg)
		yylastch = (Uchar*)yytext;
	else {
		yymorfg=0;
		yylastch = (Uchar*)yytext+yyleng;
		}
	for(;;){
		lsp = yylstate;
		yyestate = yystate = yybgin;
		if (yyprevious==YYNEWLINE) yystate++;
		for (;;){
# ifdef LEXDEBUG
			if(debug)fprintf(yyout,"state %d\n",yystate-yysvec-1);
# endif
			yyt = yystate->yystoff;
			if(yyt == yycrank){		/* may not be any transitions */
				yyz = yystate->yyother;
				if(yyz == 0)break;
				if(yyz->yystoff == yycrank)break;
				}
			*yylastch++ = yych = input();
		tryagain:
# ifdef LEXDEBUG
			if(debug){
				fprintf(yyout,"char ");
				allprint(yych);
				putchar('\n');
				}
# endif
			yyr = yyt;
			if ( (int)yyt > (int)yycrank){
				yyt = yyr + yych;
				if (yyt <= yytop && yyt->verify+yysvec == yystate){
					if(yyt->advance+yysvec == YYLERR)	/* error transitions */
						{unput(*--yylastch);break;}
					*lsp++ = yystate = yyt->advance+yysvec;
					goto contin;
					}
				}
# ifdef YYOPTIM
			else if((int)yyt < (int)yycrank) {		/* r < yycrank */
				yyt = yyr = yycrank+(yycrank-yyt);
# ifdef LEXDEBUG
				if(debug)fprintf(yyout,"compressed state\n");
# endif
				yyt = yyt + yych;
				if(yyt <= yytop && yyt->verify+yysvec == yystate){
					if(yyt->advance+yysvec == YYLERR)	/* error transitions */
						{unput(*--yylastch);break;}
					*lsp++ = yystate = yyt->advance+yysvec;
					goto contin;
					}
				yyt = yyr + YYU(yymatch[yych]);
# ifdef LEXDEBUG
				if(debug){
					fprintf(yyout,"try fall back character ");
					allprint(YYU(yymatch[yych]));
					putchar('\n');
					}
# endif
				if(yyt <= yytop && yyt->verify+yysvec == yystate){
					if(yyt->advance+yysvec == YYLERR)	/* error transition */
						{unput(*--yylastch);break;}
					*lsp++ = yystate = yyt->advance+yysvec;
					goto contin;
					}
				}
			if ((yystate = yystate->yyother) && (yyt= yystate->yystoff) != yycrank){
# ifdef LEXDEBUG
				if(debug)fprintf(yyout,"fall back to state %d\n",yystate-yysvec-1);
# endif
				goto tryagain;
				}
# endif
			else
				{unput(*--yylastch);break;}
		contin:
# ifdef LEXDEBUG
			if(debug){
				fprintf(yyout,"state %d char ",yystate-yysvec-1);
				allprint(yych);
				putchar('\n');
				}
# endif
			;
			}
# ifdef LEXDEBUG
		if(debug){
			fprintf(yyout,"stopped at %d with ",lsp>yylstate?*(lsp-1)-yysvec-1:0);
			allprint(yych);
			putchar('\n');
			}
# endif
		while (lsp-- > yylstate){
			*yylastch-- = 0;
			if (*lsp != 0 && (yyfnd= (*lsp)->yystops) && *yyfnd > 0){
				yyolsp = lsp;
				if(yyextra[*yyfnd]){		/* must backup */
					while(yyback((*lsp)->yystops,-*yyfnd) != 1 && lsp > yylstate){
						lsp--;
						unput(*yylastch--);
						}
					}
				yyprevious = YYU(*yylastch);
				yylsp = lsp;
				yyleng = yylastch-(Uchar*)yytext+1;
				yytext[yyleng] = 0;
# ifdef LEXDEBUG
				if(debug){
					fprintf(yyout,"\nmatch '%s'", yytext);
					fprintf(yyout," action %d\n",*yyfnd);
					}
# endif
				return(*yyfnd++);
				}
			unput(*yylastch);
			}
		if (yytext[0] == 0  /* && feof(yyin) */)
			{
			yysptr=yysbuf;
			return(0);
			}
		yyprevious = input();
		yytext[0] = yyprevious;
		if (yyprevious>0)
			output(yyprevious);
		yylastch = (Uchar*)yytext;
# ifdef LEXDEBUG
		if(debug)putchar('\n');
# endif
		}
	return(0);	/* shut up the compiler; i have no idea what should be returned */
	}
yyback(int *p, int m)
{
if (p==0) return(0);
while (*p)
	{
	if (*p++ == m)
		return(1);
	}
return(0);
}
	/* the following are only used in the lex library */
yyinput(void){
	return(input());
}
void
yyoutput(int c)
{
	output(c);
}
void
yyunput(int c)
{
	unput(c);
}