n1.c

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

		if (i = vmot()) {
			return(i);
		}
		goto g0;
	case 'h': 	/* horiz mot */
		numerr.type = numerr.escarg = 0; numerr.esc = k;
		if (i = hmot())
			return(i);
		goto g0;
	case '|':	/* narrow space */
		if (NROFF)
			goto g0;
		return(makem((int)(EM)/6));
	case '^':	/* half narrow space */
		if (NROFF)
			goto g0;
		return(makem((int)(EM)/12));
	case 'w':	/* width function */
		setwd();
		goto g0;
	case 'p':	/* spread */
		spread++;
		goto g0;
	case 'N':	/* absolute character number */
		numerr.type = numerr.escarg = 0; numerr.esc = k;
		if ((i = setabs()) == 0)
			goto g0;
		return i;
	case 'H':	/* character height */
		numerr.type = numerr.escarg = 0; numerr.esc = k;
		return(setht());
	case 'S':	/* slant */
		numerr.type = numerr.escarg = 0; numerr.esc = k;
		return(setslant());
	case 'z':	/* zero with char */
		return(setz());
	case 'l':	/* hor line */
		numerr.type = numerr.escarg = 0; numerr.esc = k;
		setline();
		goto g0;
	case 'L':	/* vert line */
		numerr.type = numerr.escarg = 0; numerr.esc = k;
		setvline();
		goto g0;
	case 'D':	/* drawing function */
		numerr.type = numerr.escarg = 0; numerr.esc = k;
		setdraw();
		goto g0;
	case 'X':	/* \X'...' for copy through */
		setxon();
		goto g0;
	case 'b':	/* bracket */
		setbra();
		goto g0;
	case 'o':	/* overstrike */
		setov();
		goto g0;
	case 'k':	/* mark hor place */
		if ((k = findr(getsn())) != -1) {
			numtabp[k].val = numtabp[HP].val;
		}
		goto g0;
	case '0':	/* number space */
		return(makem(width('0' | chbits)));
	case 'x':	/* extra line space */
		numerr.type = numerr.escarg = 0; numerr.esc = k;
		if (i = xlss())
			return(i);
		goto g0;
	case 'u':	/* half em up */
	case 'r':	/* full em up */
	case 'd':	/* half em down */
		return(sethl(k));
	default:
		return(j);
	}
	/* NOTREACHED */
}

void setxon(void)	/* \X'...' for copy through */
{
	Tchar xbuf[NC];
	Tchar *i;
	Tchar c;
	int delim, k;

	if (ismot(c = getch()))
		return;
	delim = cbits(c);
	i = xbuf;
	*i++ = XON | chbits;
	while ((k = cbits(c = getch())) != delim && k != '\n' && i < xbuf+NC-1) {
		if (k == ' ')
			setcbits(c, WORDSP);
		*i++ = c | ZBIT;
	}
	*i++ = XOFF | chbits;
	*i = 0;
	pushback(xbuf);
}


char	ifilt[32] = { 0, 001, 002, 003, 0, 005, 006, 007, 010, 011, 012 };

Tchar getch0(void)
{
	int j;
	Tchar i;

again:
	if (pbp > lastpbp)
		i = *--pbp;
	else if (ip) {
		/* i = rbf(); */
		i = rbf0(ip);
		if (i == 0)
			i = rbf();
		else {
			++ip;
			if (pastend(ip)) {
				--ip;
				rbf();
			}
		}
	} else {
		if (donef || ndone)
			done(0);
		if (nx || 1) {	/* BUG: was ibufp >= eibuf, so EOF test is wrong */
			if (nfo < 0)
				ERROR "in getch0, nfo = %d", nfo WARN;
			if (nfo == 0) {
g0:
				if (nextfile()) {
					if (ip)
						goto again;
				}
			}
			nx = 0;
#ifdef UNICODE
			if (MB_CUR_MAX > 1)
				i = get1ch(ifile);
			else
#endif	/*UNICODE*/
				i = getc(ifile);
			if (i == EOF)
				goto g0;
			if (ip)
				goto again;
		}
g2:
		if (i >= 040)			/* zapped: && i < 0177 */
			goto g4;
		i = ifilt[i];
	}
	if (cbits(i) == IMP && !raw)
		goto again;
	if (i == 0 && !init && !raw) {		/* zapped:  || i == 0177 */
		goto again;
	}
g4:
	if (ismot(i))
		return i;
	if (copyf == 0 && sfbits(i) == 0)
		i |= chbits;
	if (cbits(i) == eschar && !raw)
		setcbits(i, ESC);
	return(i);
}


#ifdef UNICODE
Tchar get1ch(FILE *fp)	/* get one "character" from input, figure out what alphabet */
{
	wchar_t wc;
	char buf[100], *p;
	int i, n, c;

	for (i = 0, p = buf; i < MB_CUR_MAX; i++) {
		if ((c = getc(fp)) == EOF)
			return c;
		*p++ = c;
		if ((n = mbtowc(&wc, buf, p-buf)) >= 0)
			break;
	}
	if (n == 1)	/* real ascii, presumably */
		return wc;
	if (n == 0)
		return p[-1];	/* illegal, but what else to do? */
	if (c == EOF)
		return EOF;
	*p = 0;
	return chadd(buf, MBchar, Install);	/* add name even if haven't seen it */
}
#endif	/*UNICODE*/

void pushback(Tchar *b)
{
	Tchar *ob = b;

	while (*b++)
		;
	b--;
	while (b > ob && pbp < &pbbuf[NC-3])
		*pbp++ = *--b;
	if (pbp >= &pbbuf[NC-3]) {
		ERROR "pushback overflow" WARN;
		done(2);
	}
}

void cpushback(char *b)
{
	char *ob = b;

	while (*b++)
		;
	b--;
	while (b > ob && pbp < &pbbuf[NC-3])
		*pbp++ = *--b;
	if (pbp >= &pbbuf[NC-3]) {
		ERROR "cpushback overflow" WARN;
		done(2);
	}
}

int nextfile(void)
{
	char *p;

n0:
	if (ifile != stdin)
		fclose(ifile);
	if (ifi > 0 && !nx) {
		if (popf())
			goto n0; /* popf error */
		return(1);	 /* popf ok */
	}
	if (nx || nmfi < mflg) {
		p = mfiles[nmfi++];
		if (*p != 0)
			goto n1;
	}
	if (rargc-- <= 0) {
		if ((nfo -= mflg) && !stdi) {
			done(0);
}
		nfo++;
		numtabp[CD].val = stdi = mflg = 0;
		ifile = stdin;
		strcpy(cfname[ifi], "stdin");
		return(0);
	}
	p = (argp++)[0];
	if (rargc >= 0)
		cfname[ifi][0] = 0;
n1:
	numtabp[CD].val = 0;
	if (p[0] == '-' && p[1] == 0) {
		ifile = stdin;
		strcpy(cfname[ifi], "stdin");
	} else if ((ifile = fopen(p, "r")) == NULL) {
		ERROR "cannot open file %s", p WARN;
		nfo -= mflg;
		done(02);
	} else
		strcpy(cfname[ifi],p);
	nfo++;
	return(0);
}


popf(void)
{
	--ifi;
	if (ifi < 0) {
		ERROR "popf went negative" WARN;
		return 1;
	}
	numtabp[CD].val = cfline[ifi];	/* restore line counter */
	ip = ipl[ifi];			/* input pointer */
	ifile = ifl[ifi];		/* input FILE * */
	return(0);
}


void flushi(void)
{
	if (nflush)
		return;
	ch = 0;
	copyf++;
	while (!nlflg) {
		if (donef && frame == stk)
			break;
		getch();
	}
	copyf--;
}

/*
 * return 16-bit, ascii/alphabetic character, ignore chars with more bits,
 * (internal names), spaces and special cookies (below 040).
 * Leave STX ETX ENQ ACK and BELL in to maintain compatibility with v7 troff.
 */
getach(void)
{
	Tchar i;
	int j;

	lgf++;
	j = cbits(i = getch());
        if (ismot(i)
	    || j > SHORTMASK
	    || (j <= 040 && j != 002	/*STX*/
			&& j != 003	/*ETX*/
			&& j != 005	/*ENQ*/
			&& j != 006	/*ACK*/
			&& j != 007)) {	/*BELL*/
		ch = i;
		j = 0;
	}
	lgf--;
	return j;
}


void casenx(void)
{
	lgf++;
	skip();
	getname();
	nx++;
	if (nmfi > 0)
		nmfi--;
	strcpy(mfiles[nmfi], nextf);
	nextfile();
	nlflg++;
	ip = 0;
	pendt = 0;
	frame = stk;
	nxf = frame + 1;
}


getname(void)
{
	int j, k;
	Tchar i;

	lgf++;
	for (k = 0; k < NS - 1; k++) {
		j = getach();
		if (!j)
			break;
		nextf[k] = j;
	}
	nextf[k] = 0;
	lgf--;
	return(nextf[0]);
}


void caseso(void)
{
	FILE *fp;
	char *p, *q;

	lgf++;
	nextf[0] = 0;
	if (skip() || !getname() || (fp = fopen(nextf, "r")) == NULL || ifi >= NSO) {
		ERROR "can't open file %s", nextf WARN;
		done(02);
	}
	strcpy(cfname[ifi+1], nextf);
	cfline[ifi] = numtabp[CD].val;		/*hold line counter*/
	numtabp[CD].val = 0;
	flushi();
	ifl[ifi] = ifile;
	ifile = fp;
	ipl[ifi] = ip;
	ip = 0;
	nx++;
	nflush++;
	ifi++;
}

void caself(void)	/* set line number and file */
{
	int n;

	if (skip())
		return;
	n = atoi0();
	if (!nonumb)
		cfline[ifi] = numtabp[CD].val = n - 1;
	if (!skip())
		if (getname()) {	/* eats '\n' ? */
			strcpy(cfname[ifi], nextf);
			if (!nonumb)
				numtabp[CD].val--;
		}
}

void cpout(FILE *fin, char *token)
{
	int n;
	char buf[1024];

	if (token) {	/* BUG: There should be no NULL bytes in input */
		char *newl = buf;
		while ((fgets(buf, sizeof buf, fin)) != NULL) {
			if (newl) {
				numtabp[CD].val++; /* line number */
				if (strcmp(token, buf) == 0)
					return;
			}
			newl = strchr(buf, '\n');
			fputs(buf, ptid);
		}
	} else {
		while ((n = fread(buf, sizeof *buf, sizeof buf, fin)) > 0)
			fwrite(buf, n, 1, ptid);
		fclose(fin);
	}
}

void casecf(void)
{	/* copy file without change */
	FILE *fd;
	char *eof, *p;
	extern int hpos, esc, po;

	/* this may not make much sense in nroff... */

	lgf++;
	nextf[0] = 0;
	if (!skip() && getname()) {
		if (strncmp("<<", nextf, 2) != 0) {
			if ((fd = fopen(nextf, "r")) == NULL) {
				ERROR "can't open file %s", nextf WARN;
				done(02);
			}
			eof = (char *) NULL;
		} else {	/* current file */
			if (pbp > lastpbp || ip) {
				ERROR "casecf: not reading from file" WARN;
				done(02);
			}
			eof = &nextf[2];
			if (!*eof)  {
				ERROR "casecf: missing end of input token" WARN;
				done(02);
			}
			p = eof;
			while(*++p)
				;
			*p++ = '\n';
			*p = 0;
			fd = ifile;
		}
	} else {
		ERROR "casecf: no argument" WARN;
		lgf--;
		return;
	}
	lgf--;

	/* make it into a clean state, be sure that everything is out */
	tbreak();
	hpos = po;
	esc = 0;
	ptesc();	/* to left margin */
	esc = un;
	ptesc();
	ptlead();
	ptps();
	ptfont();
	flusho();
	cpout(fd, eof);
	ptps();
	ptfont();
}

void getline(char *s, int n)	/* get rest of input line into s */
{
	int i;

	lgf++;
	copyf++;
	skip();
	for (i = 0; i < n-1; i++)
		if ((s[i] = cbits(getch())) == '\n' || s[i] == RIGHT)
			break;
	s[i] = 0;
	copyf--;
	lgf--;
}

void casesy(void)	/* call system */
{
	char sybuf[NTM];

	getline(sybuf, NTM);
	system(sybuf);
}


void getpn(char *a)
{
	int n, neg;

	if (*a == 0)
		return;
	neg = 0;
	for ( ; *a; a++)
		switch (*a) {
		case '+':
		case ',':
			continue;
		case '-':
			neg = 1;
			continue;
		default:
			n = 0;
			if (isdigit(*a)) {
				do
					n = 10 * n + *a++ - '0';
				while (isdigit(*a));
				a--;
			} else
				n = 9999;
			*pnp++ = neg ? -n : n;
			neg = 0;
			if (pnp >= &pnlist[NPN-2]) {
				ERROR "too many page numbers" WARN;
				done3(-3);
			}
		}
	if (neg)
		*pnp++ = -9999;
	*pnp = -INT_MAX;
	print = 0;
	pnp = pnlist;
	if (*pnp != -INT_MAX)
		chkpn();
}


void setrpt(void)
{
	Tchar i, j;

	copyf++;
	raw++;
	i = getch0();
	copyf--;
	raw--;
	if ((long) i < 0 || cbits(j = getch0()) == RPT)
		return;
	while (i > 0 && pbp < &pbbuf[NC-3]) {
		i--;
		*pbp++ = j;
	}
}