dc.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

				readptr++;
			*readptr = p;
			if(p != 0)
				rewind(p);
			else {
				if((c = readc()) != '\n')
					unreadc(c);
			}
			continue;
		case '?':
			if(++readptr == &readstk[RDSKSZ]) {
				error("nesting depth\n");
			}
			*readptr = 0;
			fsave = curfile;
			curfile = &bin;
			while((c = readc()) == '!')
				command();
			p = salloc(0);
			sputc(p,c);
			while((c = readc()) != '\n') {
				sputc(p,c);
				if(c == '\\')
					sputc(p,readc());
			}
			curfile = fsave;
			*readptr = p;
			continue;
		case '!':
			if(command() == 1)
				goto execute;
			continue;
		case '<':
		case '>':
		case '=':
			if(cond(c) == 1)
				goto execute;
			continue;
		default:
			Bprint(&bout,"%o is unimplemented\n",c);
		}
	}
}

Blk*
div(Blk *ddivd, Blk *ddivr)
{
	int divsign, remsign, offset, divcarry,
		carry, dig, magic, d, dd, under, first;
	long c, td, cc;
	Blk *ps, *px, *p, *divd, *divr;

	dig = 0;
	under = 0;
	divcarry = 0;
	rem = 0;
	p = salloc(0);
	if(length(ddivr) == 0) {
		pushp(ddivr);
		Bprint(&bout,"divide by 0\n");
		return(p);
	}
	divsign = remsign = first = 0;
	divr = ddivr;
	fsfile(divr);
	if(sbackc(divr) == -1) {
		divr = copy(ddivr,length(ddivr));
		chsign(divr);
		divsign = ~divsign;
	}
	divd = copy(ddivd,length(ddivd));
	fsfile(divd);
	if(sfbeg(divd) == 0 && sbackc(divd) == -1) {
		chsign(divd);
		divsign = ~divsign;
		remsign = ~remsign;
	}
	offset = length(divd) - length(divr);
	if(offset < 0)
		goto ddone;
	seekc(p,offset+1);
	sputc(divd,0);
	magic = 0;
	fsfile(divr);
	c = sbackc(divr);
	if(c < 10)
		magic++;
	c = c * 100 + (sfbeg(divr)?0:sbackc(divr));
	if(magic>0){
		c = (c * 100 +(sfbeg(divr)?0:sbackc(divr)))*2;
		c /= 25;
	}
	while(offset >= 0) {
		first++;
		fsfile(divd);
		td = sbackc(divd) * 100;
		dd = sfbeg(divd)?0:sbackc(divd);
		td = (td + dd) * 100;
		dd = sfbeg(divd)?0:sbackc(divd);
		td = td + dd;
		cc = c;
		if(offset == 0)
			td++;
		else
			cc++;
		if(magic != 0)
			td = td<<3;
		dig = td/cc;
		under=0;
		if(td%cc < 8  && dig > 0 && magic) {
			dig--;
			under=1;
		}
		rewind(divr);
		rewind(divxyz);
		carry = 0;
		while(sfeof(divr) == 0) {
			d = sgetc(divr)*dig+carry;
			carry = d / 100;
			salterc(divxyz,d%100);
		}
		salterc(divxyz,carry);
		rewind(divxyz);
		seekc(divd,offset);
		carry = 0;
		while(sfeof(divd) == 0) {
			d = slookc(divd);
			d = d-(sfeof(divxyz)?0:sgetc(divxyz))-carry;
			carry = 0;
			if(d < 0) {
				d += 100;
				carry = 1;
			}
			salterc(divd,d);
		}
		divcarry = carry;
		backc(p);
		salterc(p,dig);
		backc(p);
		fsfile(divd);
		d=sbackc(divd);
		if((d != 0) && /*!divcarry*/ (offset != 0)) {
			d = sbackc(divd) + 100;
			salterc(divd,d);
		}
		if(--offset >= 0)
			divd->wt--;
	}
	if(under) {	/* undershot last - adjust*/
		px = copy(divr,length(divr));	/*11/88 don't corrupt ddivr*/
		chsign(px);
		ps = add(px,divd);
		fsfile(ps);
		if(length(ps) > 0 && sbackc(ps) < 0) {
			release(ps);	/*only adjust in really undershot*/
		} else {
			release(divd);
			salterc(p, dig+1);
			divd=ps;
		}
	}
	if(divcarry != 0) {
		salterc(p,dig-1);
		salterc(divd,-1);
		ps = add(divr,divd);
		release(divd);
		divd = ps;
	}

	rewind(p);
	divcarry = 0;
	while(sfeof(p) == 0){
		d = slookc(p)+divcarry;
		divcarry = 0;
		if(d >= 100){
			d -= 100;
			divcarry = 1;
		}
		salterc(p,d);
	}
	if(divcarry != 0)salterc(p,divcarry);
	fsfile(p);
	while(sfbeg(p) == 0) {
		if(sbackc(p) != 0)
			break;
		truncate(p);
	}
	if(divsign < 0)
		chsign(p);
	fsfile(divd);
	while(sfbeg(divd) == 0) {
		if(sbackc(divd) != 0)
			break;
		truncate(divd);
	}
ddone:
	if(remsign<0)
		chsign(divd);
	if(divr != ddivr)
		release(divr);
	rem = divd;
	return(p);
}

int
dscale(void)
{
	Blk *dd, *dr, *r;
	int c;

	dr = pop();
	EMPTYS;
	dd = pop();
	EMPTYSR(dr);
	fsfile(dd);
	skd = sunputc(dd);
	fsfile(dr);
	skr = sunputc(dr);
	if(sfbeg(dr) == 1 || (sfbeg(dr) == 0 && sbackc(dr) == 0)) {
		sputc(dr,skr);
		pushp(dr);
		Bprint(&bout,"divide by 0\n");
		return(1);
	}
	if(sfbeg(dd) == 1 || (sfbeg(dd) == 0 && sbackc(dd) == 0)) {
		sputc(dd,skd);
		pushp(dd);
		return(1);
	}
	c = k-skd+skr;
	if(c < 0)
		r = removr(dd,-c);
	else {
		r = add0(dd,c);
		irem = 0;
	}
	arg1 = r;
	arg2 = dr;
	savk = k;
	return(0);
}

Blk*
removr(Blk *p, int n)
{
	int nn, neg;
	Blk *q, *s, *r;

	fsfile(p);
	neg = sbackc(p);
	if(neg < 0)
		chsign(p);
	rewind(p);
	nn = (n+1)/2;
	q = salloc(nn);
	while(n>1) {
		sputc(q,sgetc(p));
		n -= 2;
	}
	r = salloc(2);
	while(sfeof(p) == 0)
		sputc(r,sgetc(p));
	release(p);
	if(n == 1){
		s = div(r,tenptr);
		release(r);
		rewind(rem);
		if(sfeof(rem) == 0)
			sputc(q,sgetc(rem));
		release(rem);
		if(neg < 0){
			chsign(s);
			chsign(q);
			irem = q;
			return(s);
		}
		irem = q;
		return(s);
	}
	if(neg < 0) {
		chsign(r);
		chsign(q);
		irem = q;
		return(r);
	}
	irem = q;
	return(r);
}

Blk*
dcsqrt(Blk *p)
{
	Blk *t, *r, *q, *s;
	int c, n, nn;

	n = length(p);
	fsfile(p);
	c = sbackc(p);
	if((n&1) != 1)
		c = c*100+(sfbeg(p)?0:sbackc(p));
	n = (n+1)>>1;
	r = salloc(n);
	zero(r);
	seekc(r,n);
	nn=1;
	while((c -= nn)>=0)
		nn+=2;
	c=(nn+1)>>1;
	fsfile(r);
	backc(r);
	if(c>=100) {
		c -= 100;
		salterc(r,c);
		sputc(r,1);
	} else
		salterc(r,c);
	for(;;){
		q = div(p,r);
		s = add(q,r);
		release(q);
		release(rem);
		q = div(s,sqtemp);
		release(s);
		release(rem);
		s = copy(r,length(r));
		chsign(s);
		t = add(s,q);
		release(s);
		fsfile(t);
		nn = sfbeg(t)?0:sbackc(t);
		if(nn>=0)
			break;
		release(r);
		release(t);
		r = q;
	}
	release(t);
	release(q);
	release(p);
	return(r);
}

Blk*
dcexp(Blk *base, Blk *ex)
{
	Blk *r, *e, *p, *e1, *t, *cp;
	int temp, c, n;

	r = salloc(1);
	sputc(r,1);
	p = copy(base,length(base));
	e = copy(ex,length(ex));
	fsfile(e);
	if(sfbeg(e) != 0)
		goto edone;
	temp=0;
	c = sbackc(e);
	if(c<0) {
		temp++;
		chsign(e);
	}
	while(length(e) != 0) {
		e1=div(e,sqtemp);
		release(e);
		e = e1;
		n = length(rem);
		release(rem);
		if(n != 0) {
			e1=mult(p,r);
			release(r);
			r = e1;
		}
		t = copy(p,length(p));
		cp = mult(p,t);
		release(p);
		release(t);
		p = cp;
	}
	if(temp != 0) {
		if((c = length(base)) == 0) {
			goto edone;
		}
		if(c>1)
			create(r);
		else {
			rewind(base);
			if((c = sgetc(base))<=1) {
				create(r);
				sputc(r,c);
			} else
				create(r);
		}
	}
edone:
	release(p);
	release(e);
	return(r);
}

void
init(int argc, char *argv[])
{
	Sym *sp;
	Dir *d;

	ARGBEGIN {
	default:
		dbg = 1;
		break;
	} ARGEND
	ifile = 1;
	curfile = &bin;
	if(*argv){
		d = dirstat(*argv);
		if(d == nil) {
			fprint(2, "dc: can't open file %s\n", *argv);
			exits("open");
		}
		if(d->mode & DMDIR) {
			fprint(2, "dc: file %s is a directory\n", *argv);
			exits("open");
		}
		free(d);
		if((curfile = Bopen(*argv, OREAD)) == 0) {
			fprint(2,"dc: can't open file %s\n", *argv);
			exits("open");
		}
	}
/*	dummy = malloc(0);  /* prepare for garbage-collection */
	scalptr = salloc(1);
	sputc(scalptr,0);
	basptr = salloc(1);
	sputc(basptr,10);
	obase=10;
	logten=log2(10L);
	ll=70;
	fw=1;
	fw1=0;
	tenptr = salloc(1);
	sputc(tenptr,10);
	obase=10;
	inbas = salloc(1);
	sputc(inbas,10);
	sqtemp = salloc(1);
	sputc(sqtemp,2);
	chptr = salloc(0);
	strptr = salloc(0);
	divxyz = salloc(0);
	stkbeg = stkptr = &stack[0];
	stkend = &stack[STKSZ];
	stkerr = 0;
	readptr = &readstk[0];
	k=0;
	sp = sptr = &symlst[0];
	while(sptr < &symlst[TBLSZ]) {
		sptr->next = ++sp;
		sptr++;
	}
	sptr->next=0;
	sfree = &symlst[0];
}

void
pushp(Blk *p)
{
	if(stkptr == stkend) {
		Bprint(&bout,"out of stack space\n");
		return;
	}
	stkerr=0;
	*++stkptr = p;
	return;
}

Blk*
pop(void)
{
	if(stkptr == stack) {
		stkerr=1;
		return(0);
	}
	return(*stkptr--);
}

Blk*
readin(void)
{
	Blk *p, *q;
	int dp, dpct, c;

	dp = dpct=0;
	p = salloc(0);
	for(;;){
		c = readc();
		switch(c) {
		case '.':
			if(dp != 0)
				goto gotnum;
			dp++;
			continue;
		case '\\':
			readc();
			continue;
		default:
			if(c >= 'A' && c <= 'F')
				c = c - 'A' + 10;
			else
			if(c >= '0' && c <= '9')
				c -= '0';
			else
				goto gotnum;
			if(dp != 0) {
				if(dpct >= 99)
					continue;
				dpct++;
			}
			create(chptr);
			if(c != 0)
				sputc(chptr,c);
			q = mult(p,inbas);
			release(p);
			p = add(chptr,q);
			release(q);
		}
	}
gotnum:
	unreadc(c);
	if(dp == 0) {
		sputc(p,0);
		return(p);
	} else {
		q = scale(p,dpct);
		return(q);
	}
}

/*
 * returns pointer to struct with ct 0's & p
 */
Blk*
add0(Blk *p, int ct)
{
	Blk *q, *t;

	q = salloc(length(p)+(ct+1)/2);
	while(ct>1) {
		sputc(q,0);
		ct -= 2;
	}
	rewind(p);
	while(sfeof(p) == 0) {
		sputc(q,sgetc(p));
	}
	release(p);
	if(ct == 1) {
		t = mult(tenptr,q);
		release(q);
		return(t);
	}
	return(q);
}

Blk*
mult(Blk *p, Blk *q)
{
	Blk *mp, *mq, *mr;
	int sign, offset, carry;
	int cq, cp, mt, mcr;

	offset = sign = 0;
	fsfile(p);
	mp = p;
	if(sfbeg(p) == 0) {
		if(sbackc(p)<0) {
			mp = copy(p,length(p));
			chsign(mp);
			sign = ~sign;
		}
	}
	fsfile(q);
	mq = q;
	if(sfbeg(q) == 0){
		if(sbackc(q)<0) {
			mq = copy(q,length(q));
			chsign(mq);
			sign = ~sign;
		}
	}
	mr = salloc(length(mp)+length(mq));
	zero(mr);
	rewind(mq);
	while(sfeof(mq) == 0) {
		cq = sgetc(mq);
		rewind(mp);
		rewind(mr);
		mr->rd += offset;
		carry=0;
		while(sfeof(mp) == 0) {
			cp = sgetc(mp);
			mcr = sfeof(mr)?0:slookc(mr);
			mt = cp*cq + carry + mcr;
			carry = mt/100;
			salterc(mr,mt%100);
		}
		offset++;
		if(carry != 0) {
			mcr = sfeof(mr)?0:slookc(mr);
			salterc(mr,mcr+carry);
		}
	}
	if(sign < 0) {
		chsign(mr);
	}
	if(mp != p)
		release(mp);
	if(mq != q)
		release(mq);
	return(mr);
}

void
chsign(Blk *p)
{
	int carry;
	char ct;

	carry=0;
	rewind(p);
	while(sfeof(p) == 0) {
		ct=100-slookc(p)-carry;
		carry=1;
		if(ct>=100) {
			ct -= 100;
			carry=0;
		}
		salterc(p,ct);
	}
	if(carry != 0) {
		sputc(p,-1);
		fsfile(p);
		backc(p);
		ct = sbackc(p);
		if(ct == 99 /*&& !sfbeg(p)*/) {
			truncate(p);
			sputc(p,-1);
		}
	} else{
		fsfile(p);
		ct = sbackc(p);
		if(ct == 0)
			truncate(p);
	}
	return;
}

int
readc(void)
{
loop:
	if((readptr != &readstk[0]) && (*readptr != 0)) {
		if(sfeof(*readptr) == 0)
			return(lastchar = sgetc(*readptr));
		release(*readptr);
		readptr--;
		goto loop;
	}
	lastchar = Bgetc(curfile);
	if(lastchar != -1)
		return(lastchar);
	if(readptr != &readptr[0]) {
		readptr--;
		if(*readptr == 0)
			curfile = &bin;
		goto loop;
	}
	if(curfile != &bin) {
		Bterm(curfile);
		curfile = &bin;
		goto loop;
	}
	exits(0);
	return 0;	/* shut up ken */
}

void
unreadc(char c)
{

	if((readptr != &readstk[0]) && (*readptr != 0)) {
		sungetc(*readptr,c);
	} else
		Bungetc(curfile);
	return;
}

void
binop(char c)
{
	Blk *r;

	r = 0;
	switch(c) {
	case '+':
		r = add(arg1,arg2);
		break;
	case '*':
		r = mult(arg1,arg2);
		break;
	case '/':
		r = div(arg1,arg2);
		break;
	}
	release(arg1);
	release(arg2);
	sputc(r,savk);
	pushp(r);
}

void
dcprint(Blk *hptr)
{
	Blk *p, *q, *dec;
	int dig, dout, ct, sc;

	rewind(hptr);
	while(sfeof(hptr) == 0) {
		if(sgetc(hptr)>99) {
			rewind(hptr);
			while(sfeof(hptr) == 0) {
				Bprint(&bout,"%c",sgetc(hptr));
			}
			Bprint(&bout,"\n");
			return;
		}
	}
	fsfile(hptr);
	sc = sbackc(hptr);
	if(sfbeg(hptr) != 0) {
		Bprint(&bout,"0\n");
		return;
	}
	count = ll;
	p = copy(hptr,length(hptr));
	sclobber(p);
	fsfile(p);
	if(sbackc(p)<0) {
		chsign(p);
		OUTC('-');
	}
	if((obase == 0) || (obase == -1)) {
		oneot(p,sc,'d');
		return;
	}
	if(obase == 1) {
		oneot(p,sc,'1');
		return;
	}
	if(obase == 10) {
		tenot(p,sc);
		return;
	}
	/* sleazy hack to scale top of stack - divide by 1 */
	pushp(p);
	sputc(p, sc);
	p=salloc(0);
	create(p);
	sputc(p, 1);