n3.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

	}
	nextb = (Offset) i * BLK;
	return nextb;
}


void ffree(Offset i)	/* free list of blocks starting at blist(o) */
{			/* (doesn't actually free the blocks, just the pointers) */
	int j;

	for ( ; blist[j = bindex(i)].nextoff != -1; ) {
		if (bfree > j)
			bfree = j;
		i = blist[j].nextoff;
		blist[j].nextoff = 0;
	}
	blist[j].nextoff = 0;
}


void wbf(Tchar i)	/* store i into offset, get ready for next one */
{
	int j, off;

	if (!offset)
		return;
	j = bindex(offset);
	if (i == 0)
		contabp[savslot].emx = offset;
	off = boffset(offset);
	blist[j].bp[off++] = i;
	offset++;
	if (pastend(offset)) {	/* off the end of this block */
		if (blist[j].nextoff == -1) {
			if ((nextb = alloc()) == -1) {
				ERROR "Out of temp file space" WARN;
				done2(01);
			}
			blist[j].nextoff = nextb;
		}
		offset = blist[j].nextoff;
	}
}


Tchar rbf(void)	/* return next char from blist[] block */
{
	Tchar i, j;

	if (ip == RD_OFFSET) {		/* for rdtty */
		if (j = rdtty())
			return(j);
		else
			return(popi());
	}
	
	i = rbf0(ip);
	if (i == 0) {
		if (!app)
			i = popi();
		return(i);
	}
	ip = incoff(ip);
	return(i);
}


Offset xxxincoff(Offset p)		/* get next blist[] block */
{
	p++;
	if (pastend(p)) {		/* off the end of this block */
		if ((p = blist[bindex(p-1)].nextoff) == -1) {	/* and nothing was allocated after it */
			ERROR "Bad storage allocation" WARN;
			done2(-5);
		}
	}
	return(p);
}


Tchar popi(void)
{
	Stack *p;

	if (frame == stk)
		return(0);
	if (strflg)
		strflg--;
	p = nxf = frame;
	p->nargs = 0;
	frame = p->pframe;
	ip = p->pip;
	pendt = p->ppendt;
	lastpbp = p->lastpbp;
	return(p->pch);
}

/*
 *	test that the end of the allocation is above a certain location
 *	in memory
 */
#define SPACETEST(base, size) \
	if ((char*)base + size >= (char*)stk+STACKSIZE) \
		ERROR "Stacksize overflow in n3" WARN

Offset pushi(Offset newip, int  mname)
{
	Stack *p;

	SPACETEST(nxf, sizeof(Stack));
	p = nxf;
	p->pframe = frame;
	p->pip = ip;
	p->ppendt = pendt;
	p->pch = ch;
	p->lastpbp = lastpbp;
	p->mname = mname;
	lastpbp = pbp;
	pendt = ch = 0;
	frame = nxf;
	if (nxf->nargs == 0) 
		nxf += 1;
	else 
		nxf = (Stack *)argtop;
	return(ip = newip);
}


void *setbrk(int x)
{
	char *i;

	if ((i = (char *) calloc(x, 1)) == 0) {
		ERROR "Core limit reached" WARN;
		edone(0100);
	}
	return(i);
}


int getsn(void)
{
	int i;

	if ((i = getach()) == 0)
		return(0);
	if (i == '(')
		return(getrq());
	else 
		return(i);
}


Offset setstr(void)
{
	int i, j;

	lgf++;
	if ((i = getsn()) == 0 || (j = findmn(i)) == -1 || !contabp[j].mx) {
		lgf--;
		return(0);
	} else {
		SPACETEST(nxf, sizeof(Stack));
		nxf->nargs = 0;
		strflg++;
		lgf--;
		return pushi(contabp[j].mx, i);
	}
}



void collect(void)
{
	int j;
	Tchar i, *strp, *lim, **argpp, **argppend;
	int quote;
	Stack *savnxf;

	copyf++;
	nxf->nargs = 0;
	savnxf = nxf;
	if (skip())
		goto rtn;

	{
		char *memp;
		memp = (char *)savnxf;
		/*
		 *	1 s structure for the macro descriptor
		 *	APERMAC Tchar *'s for pointers into the strings
		 *	space for the Tchar's themselves
		 */
		memp += sizeof(Stack);
		/*
		 *	CPERMAC = the total # of characters for ALL arguments
		 */
#define	CPERMAC	200
#define	APERMAC	9
		memp += APERMAC * sizeof(Tchar *);
		memp += CPERMAC * sizeof(Tchar);
		nxf = (Stack *)memp;
	}
	lim = (Tchar *)nxf;
	argpp = (Tchar **)(savnxf + 1);
	argppend = &argpp[APERMAC];
	SPACETEST(argppend, sizeof(Tchar *));
	strp = (Tchar *)argppend;
	/*
	 *	Zero out all the string pointers before filling them in.
	 */
	for (j = 0; j < APERMAC; j++)
		argpp[j] = 0;
	/* ERROR "savnxf=0x%x,nxf=0x%x,argpp=0x%x,strp=argppend=0x%x, lim=0x%x",
	 * 	savnxf, nxf, argpp, strp, lim WARN;
	 */
	strflg = 0;
	while (argpp != argppend && !skip()) {
		*argpp++ = strp;
		quote = 0;
		if (cbits(i = getch()) == '"')
			quote++;
		else 
			ch = i;
		while (1) {
			i = getch();
/* fprintf(stderr, "collect %c %d\n", cbits(i), cbits(i)); */
			if (nlflg || (!quote && argpp != argppend && cbits(i) == ' '))
				break;	/* collects rest into $9 */
			if (   quote
			    && cbits(i) == '"'
			    && cbits(i = getch()) != '"') {
				ch = i;
				break;
			}
			*strp++ = i;
			if (strflg && strp >= lim) {
				/* ERROR "strp=0x%x, lim = 0x%x", strp, lim WARN; */
				ERROR "Macro argument too long" WARN;
				copyf--;
				edone(004);
			}
			SPACETEST(strp, 3 * sizeof(Tchar));
		}
		*strp++ = 0;
	}
	nxf = savnxf;
	nxf->nargs = argpp - (Tchar **)(savnxf + 1);
	argtop = strp;
rtn:
	copyf--;
}


void seta(void)
{
	int i;

	i = cbits(getch()) - '0';
	if (i > 0 && i <= APERMAC && i <= frame->nargs)
		pushback(*(((Tchar **)(frame + 1)) + i - 1));
}


void caseda(void)
{
	app++;
	casedi();
}

void casegd(void)
{
	int i, j;

	skip();
	if ((i = getrq()) == 0)
		return;
	if ((j = findmn(i)) >= 0) {
		if (contabp[j].divsiz != NULL) {
			numtabp[DN].val = contabp[j].divsiz->dix;
			numtabp[DL].val = contabp[j].divsiz->diy;
		}
	}
}

#define FINDDIV(o) if ((o =  findmn(dip->curd)) < 0) \
			ERROR "lost diversion %s", unpair(dip->curd) WARN

void casedi(void)
{
	int i, j, *k;

	lgf++;
	if (skip() || (i = getrq()) == 0) {
		if (dip != d) {
			FINDDIV(savslot);
			wbf((Tchar)0);
		}
		if (dilev > 0) {
			numtabp[DN].val = dip->dnl;
			numtabp[DL].val = dip->maxl;
			FINDDIV(j);
			if ((contabp[j].divsiz = (Divsiz *) malloc(sizeof(Divsiz))) == NULL) {
				ERROR "Cannot alloc diversion size" WARN;
				done2(1);
			} else {
				contabp[j].divsiz->dix = numtabp[DN].val;
				contabp[j].divsiz->diy = numtabp[DL].val;
			}
			dip = &d[--dilev];
			offset = dip->op;
		}
		goto rtn;
	}
	if (++dilev == NDI) {
		--dilev;
		ERROR "Diversions nested too deep" WARN;
		edone(02);
	}
	if (dip != d) {
		FINDDIV(j);
		savslot = j;
		wbf((Tchar)0);
	}
	diflg++;
	dip = &d[dilev];
	dip->op = finds(i);
	dip->curd = i;
	clrmn(oldmn);
	k = (int *) & dip->dnl;
	for (j = 0; j < 10; j++)
		k[j] = 0;	/*not op and curd*/
rtn:
	app = 0;
	diflg = 0;
}


void casedt(void)
{
	lgf++;
	dip->dimac = dip->ditrap = dip->ditf = 0;
	skip();
	dip->ditrap = vnumb((int *)0);
	if (nonumb)
		return;
	skip();
	dip->dimac = getrq();
}

#define LNSIZE 4000
void casetl(void)
{
	int j;
	int w[3];
	Tchar buf[LNSIZE];
	Tchar *tp;
	Tchar i, delim;

 	/*
 	 * bug fix
 	 *
 	 * if .tl is the first thing in the file, the p1
 	 * doesn't come out, also the pagenumber will be 0
 	 *
 	 * tends too confuse the device filter (and the user as well)
 	 */
 	if (dip == d && numtabp[NL].val == -1)
 		newline(1);
	dip->nls = 0;
	skip();
	if (ismot(delim = getch())) {
		ch = delim;
		delim = '\'';
	} else 
		delim = cbits(delim);
	tp = buf;
	numtabp[HP].val = 0;
	w[0] = w[1] = w[2] = 0;
	j = 0;
	while (cbits(i = getch()) != '\n') {
		if (cbits(i) == cbits(delim)) {
			if (j < 3)
				w[j] = numtabp[HP].val;
			numtabp[HP].val = 0;
			if (w[j] != 0)
				*tp++ = WORDSP;
			j++;
			*tp++ = 0;
		} else {
			if (cbits(i) == pagech) {
				setn1(numtabp[PN].val, numtabp[findr('%')].fmt,
				      i&SFMASK);
				continue;
			}
			numtabp[HP].val += width(i);
			if (tp < &buf[LNSIZE-10]) {
				if (cbits(i) == ' ' && *tp != WORDSP)
					*tp++ = WORDSP;
				*tp++ = i;
			} else {
				ERROR "Overflow in casetl" WARN;
			}
		}
	}
	if (j<3)
		w[j] = numtabp[HP].val;
	*tp++ = 0;
	*tp++ = 0;
	*tp = 0;
	tp = buf;
	if (NROFF)
		horiz(po);
	while (i = *tp++)
		pchar(i);
	if (w[1] || w[2])
		horiz(j = quant((lt - w[1]) / 2 - w[0], HOR));
	while (i = *tp++)
		pchar(i);
	if (w[2]) {
		horiz(lt - w[0] - w[1] - w[2] - j);
		while (i = *tp++)
			pchar(i);
	}
	newline(0);
	if (dip != d) {
		if (dip->dnl > dip->hnl)
			dip->hnl = dip->dnl;
	} else {
		if (numtabp[NL].val > dip->hnl)
			dip->hnl = numtabp[NL].val;
	}
}


void casepc(void)
{
	pagech = chget(IMP);
}


void casepm(void)
{
	int i, k;
	int xx, cnt, tcnt, kk, tot;
	Offset j;

	kk = cnt = tcnt = 0;
	tot = !skip();
	stackdump();
	for (i = 0; i < nm; i++) {
		if ((xx = contabp[i].rq) == 0 || contabp[i].mx == 0)
			continue;
		tcnt++;
		j = contabp[i].mx;
		for (k = 1; (j = blist[bindex(j)].nextoff) != -1; )
			k++; 
		cnt++;
		kk += k;
		if (!tot)
			fprintf(stderr, "%-2.2s %d\n", unpair(xx), k);
	}
	fprintf(stderr, "pm: total %d, macros %d, space %d\n", tcnt, cnt, kk);
}

void stackdump(void)	/* dumps stack of macros in process */
{
	Stack *p;

	if (frame != stk) {
		fprintf(stderr, "stack: ");
		for (p = frame; p != stk; p = p->pframe)
			fprintf(stderr, "%s ", unpair(p->mname));
		fprintf(stderr, "\n");
	}
}