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

	sputc(p, 0);
	pushp(p);
	if(dscale() != 0)
		return;
	p = div(arg1, arg2);
	release(arg1);
	release(arg2);
	sc = savk;

	create(strptr);
	dig = logten*sc;
	dout = ((dig/10) + dig) / logo;
	dec = getdec(p,sc);
	p = removc(p,sc);
	while(length(p) != 0) {
		q = div(p,basptr);
		release(p);
		p = q;
		(*outdit)(rem,0);
	}
	release(p);
	fsfile(strptr);
	while(sfbeg(strptr) == 0)
		OUTC(sbackc(strptr));
	if(sc == 0) {
		release(dec);
		Bprint(&bout,"\n");
		return;
	}
	create(strptr);
	OUTC('.');
	ct=0;
	do {
		q = mult(basptr,dec);
		release(dec);
		dec = getdec(q,sc);
		p = removc(q,sc);
		(*outdit)(p,1);
	} while(++ct < dout);
	release(dec);
	rewind(strptr);
	while(sfeof(strptr) == 0)
		OUTC(sgetc(strptr));
	Bprint(&bout,"\n");
}

Blk*
getdec(Blk *p, int sc)
{
	int cc;
	Blk *q, *t, *s;

	rewind(p);
	if(length(p)*2 < sc) {
		q = copy(p,length(p));
		return(q);
	}
	q = salloc(length(p));
	while(sc >= 1) {
		sputc(q,sgetc(p));
		sc -= 2;
	}
	if(sc != 0) {
		t = mult(q,tenptr);
		s = salloc(cc = length(q));
		release(q);
		rewind(t);
		while(cc-- > 0)
			sputc(s,sgetc(t));
		sputc(s,0);
		release(t);
		t = div(s,tenptr);
		release(s);
		release(rem);
		return(t);
	}
	return(q);
}

void
tenot(Blk *p, int sc)
{
	int c, f;

	fsfile(p);
	f=0;
	while((sfbeg(p) == 0) && ((p->rd-p->beg-1)*2 >= sc)) {
		c = sbackc(p);
		if((c<10) && (f == 1))
			Bprint(&bout,"0%d",c);
		else
			Bprint(&bout,"%d",c);
		f=1;
		TEST2;
	}
	if(sc == 0) {
		Bprint(&bout,"\n");
		release(p);
		return;
	}
	if((p->rd-p->beg)*2 > sc) {
		c = sbackc(p);
		Bprint(&bout,"%d.",c/10);
		TEST2;
		OUTC(c%10 +'0');
		sc--;
	} else {
		OUTC('.');
	}
	while(sc>(p->rd-p->beg)*2) {
		OUTC('0');
		sc--;
	}
	while(sc > 1) {
		c = sbackc(p);
		if(c<10)
			Bprint(&bout,"0%d",c);
		else
			Bprint(&bout,"%d",c);
		sc -= 2;
		TEST2;
	}
	if(sc == 1) {
		OUTC(sbackc(p)/10 +'0');
	}
	Bprint(&bout,"\n");
	release(p);
}

void
oneot(Blk *p, int sc, char ch)
{
	Blk *q;

	q = removc(p,sc);
	create(strptr);
	sputc(strptr,-1);
	while(length(q)>0) {
		p = add(strptr,q);
		release(q);
		q = p;
		OUTC(ch);
	}
	release(q);
	Bprint(&bout,"\n");
}

void
hexot(Blk *p, int flg)
{
	int c;

	USED(flg);
	rewind(p);
	if(sfeof(p) != 0) {
		sputc(strptr,'0');
		release(p);
		return;
	}
	c = sgetc(p);
	release(p);
	if(c >= 16) {
		Bprint(&bout,"hex digit > 16");
		return;
	}
	sputc(strptr,c<10?c+'0':c-10+'a');
}

void
bigot(Blk *p, int flg)
{
	Blk *t, *q;
	int neg, l;

	if(flg == 1) {
		t = salloc(0);
		l = 0;
	} else {
		t = strptr;
		l = length(strptr)+fw-1;
	}
	neg=0;
	if(length(p) != 0) {
		fsfile(p);
		if(sbackc(p)<0) {
			neg=1;
			chsign(p);
		}
		while(length(p) != 0) {
			q = div(p,tenptr);
			release(p);
			p = q;
			rewind(rem);
			sputc(t,sfeof(rem)?'0':sgetc(rem)+'0');
			release(rem);
		}
	}
	release(p);
	if(flg == 1) {
		l = fw1-length(t);
		if(neg != 0) {
			l--;
			sputc(strptr,'-');
		}
		fsfile(t);
		while(l-- > 0)
			sputc(strptr,'0');
		while(sfbeg(t) == 0)
			sputc(strptr,sbackc(t));
		release(t);
	} else {
		l -= length(strptr);
		while(l-- > 0)
			sputc(strptr,'0');
		if(neg != 0) {
			sclobber(strptr);
			sputc(strptr,'-');
		}
	}
	sputc(strptr,' ');
}

Blk*
add(Blk *a1, Blk *a2)
{
	Blk *p;
	int carry, n, size, c, n1, n2;

	size = length(a1)>length(a2)?length(a1):length(a2);
	p = salloc(size);
	rewind(a1);
	rewind(a2);
	carry=0;
	while(--size >= 0) {
		n1 = sfeof(a1)?0:sgetc(a1);
		n2 = sfeof(a2)?0:sgetc(a2);
		n = n1 + n2 + carry;
		if(n>=100) {
			carry=1;
			n -= 100;
		} else
		if(n<0) {
			carry = -1;
			n += 100;
		} else
			carry = 0;
		sputc(p,n);
	}
	if(carry != 0)
		sputc(p,carry);
	fsfile(p);
	if(sfbeg(p) == 0) {
		c = 0;
		while(sfbeg(p) == 0 && (c = sbackc(p)) == 0)
			;
		if(c != 0)
			salterc(p,c);
		truncate(p);
	}
	fsfile(p);
	if(sfbeg(p) == 0 && sbackc(p) == -1) {
		while((c = sbackc(p)) == 99) {
			if(c == -1)
				break;
		}
		skipc(p);
		salterc(p,-1);
		truncate(p);
	}
	return(p);
}

int
eqk(void)
{
	Blk *p, *q;
	int skp, skq;

	p = pop();
	EMPTYS;
	q = pop();
	EMPTYSR(p);
	skp = sunputc(p);
	skq = sunputc(q);
	if(skp == skq) {
		arg1=p;
		arg2=q;
		savk = skp;
		return(0);
	}
	if(skp < skq) {
		savk = skq;
		p = add0(p,skq-skp);
	} else {
		savk = skp;
		q = add0(q,skp-skq);
	}
	arg1=p;
	arg2=q;
	return(0);
}

Blk*
removc(Blk *p, int n)
{
	Blk *q, *r;

	rewind(p);
	while(n>1) {
		skipc(p);
		n -= 2;
	}
	q = salloc(2);
	while(sfeof(p) == 0)
		sputc(q,sgetc(p));
	if(n == 1) {
		r = div(q,tenptr);
		release(q);
		release(rem);
		q = r;
	}
	release(p);
	return(q);
}

Blk*
scalint(Blk *p)
{
	int n;

	n = sunputc(p);
	p = removc(p,n);
	return(p);
}

Blk*
scale(Blk *p, int n)
{
	Blk *q, *s, *t;

	t = add0(p,n);
	q = salloc(1);
	sputc(q,n);
	s = dcexp(inbas,q);
	release(q);
	q = div(t,s);
	release(t);
	release(s);
	release(rem);
	sputc(q,n);
	return(q);
}

int
subt(void)
{
	arg1=pop();
	EMPTYS;
	savk = sunputc(arg1);
	chsign(arg1);
	sputc(arg1,savk);
	pushp(arg1);
	if(eqk() != 0)
		return(1);
	binop('+');
	return(0);
}

int
command(void)
{
	char line[100], *sl;
	int pid, p, c;

	switch(c = readc()) {
	case '<':
		return(cond(NL));
	case '>':
		return(cond(NG));
	case '=':
		return(cond(NE));
	default:
		sl = line;
		*sl++ = c;
		while((c = readc()) != '\n')
			*sl++ = c;
		*sl = 0;
		if((pid = fork()) == 0) {
			execl("/bin/rc","rc","-c",line,nil);
			exits("shell");
		}
		for(;;) {
			if((p = waitpid()) < 0)
				break;
			if(p== pid)
				break;
		}
		Bprint(&bout,"!\n");
		return(0);
	}
}

int
cond(char c)
{
	Blk *p;
	int cc;

	if(subt() != 0)
		return(1);
	p = pop();
	sclobber(p);
	if(length(p) == 0) {
		release(p);
		if(c == '<' || c == '>' || c == NE) {
			getstk();
			return(0);
		}
		load();
		return(1);
	}
	if(c == '='){
		release(p);
		getstk();
		return(0);
	}
	if(c == NE) {
		release(p);
		load();
		return(1);
	}
	fsfile(p);
	cc = sbackc(p);
	release(p);
	if((cc<0 && (c == '<' || c == NG)) ||
	   (cc >0) && (c == '>' || c == NL)) {
		getstk();
		return(0);
	}
	load();
	return(1);
}

void
load(void)
{
	int c;
	Blk *p, *q, *t, *s;

	c = getstk() & 0377;
	sptr = stable[c];
	if(sptr != 0) {
		p = sptr->val;
		if(c >= ARRAYST) {
			q = salloc(length(p));
			rewind(p);
			while(sfeof(p) == 0) {
				s = dcgetwd(p);
				if(s == 0) {
					putwd(q, (Blk*)0);
				} else {
					t = copy(s,length(s));
					putwd(q,t);
				}
			}
			pushp(q);
		} else {
			q = copy(p,length(p));
			pushp(q);
		}
	} else {
		q = salloc(1);
		if(c <= LASTFUN) {
			Bprint(&bout,"function %c undefined\n",c+'a'-1);
			sputc(q,'c');
			sputc(q,'0');
			sputc(q,' ');
			sputc(q,'1');
			sputc(q,'Q');
		}
		else
			sputc(q,0);
		pushp(q);
	}
}

int
log2(long n)
{
	int i;

	if(n == 0)
		return(0);
	i=31;
	if(n<0)
		return(i);
	while((n= n<<1) >0)
		i--;
	return i-1;
}

Blk*
salloc(int size)
{
	Blk *hdr;
	char *ptr;

	all++;
	lall++;
	if(all - rel > active)
		active = all - rel;
	nbytes += size;
	lbytes += size;
	if(nbytes >maxsize)
		maxsize = nbytes;
	if(size > longest)
		longest = size;
	ptr = malloc((unsigned)size);
	if(ptr == 0){
		garbage("salloc");
		if((ptr = malloc((unsigned)size)) == 0)
			ospace("salloc");
	}
	if((hdr = hfree) == 0)
		hdr = morehd();
	hfree = (Blk *)hdr->rd;
	hdr->rd = hdr->wt = hdr->beg = ptr;
	hdr->last = ptr+size;
	return(hdr);
}

Blk*
morehd(void)
{
	Blk *h, *kk;

	headmor++;
	nbytes += HEADSZ;
	hfree = h = (Blk *)malloc(HEADSZ);
	if(hfree == 0) {
		garbage("morehd");
		if((hfree = h = (Blk*)malloc(HEADSZ)) == 0)
			ospace("headers");
	}
	kk = h;
	while(h<hfree+(HEADSZ/BLK))
		(h++)->rd = (char*)++kk;
	(h-1)->rd=0;
	return(hfree);
}

Blk*
copy(Blk *hptr, int size)
{
	Blk *hdr;
	unsigned sz;
	char *ptr;

	all++;
	lall++;
	lcopy++;
	nbytes += size;
	lbytes += size;
	if(size > longest)
		longest = size;
	if(size > maxsize)
		maxsize = size;
	sz = length(hptr);
	ptr = nalloc(hptr->beg, size);
	if(ptr == 0) {
		garbage("copy");
		if((ptr = nalloc(hptr->beg, size)) == 0) {
			Bprint(&bout,"copy size %d\n",size);
			ospace("copy");
		}
	}
	if((hdr = hfree) == 0)
		hdr = morehd();
	hfree = (Blk *)hdr->rd;
	hdr->rd = hdr->beg = ptr;
	hdr->last = ptr+size;
	hdr->wt = ptr+sz;
	ptr = hdr->wt;
	while(ptr<hdr->last)
		*ptr++ = '\0';
	return(hdr);
}

void
sdump(char *s1, Blk *hptr)
{
	char *p;

	Bprint(&bout,"%s %lx rd %lx wt %lx beg %lx last %lx\n",
		s1,hptr,hptr->rd,hptr->wt,hptr->beg,hptr->last);
	p = hptr->beg;
	while(p < hptr->wt)
		Bprint(&bout,"%d ",*p++);
	Bprint(&bout,"\n");
}

void
seekc(Blk *hptr, int n)
{
	char *nn,*p;

	nn = hptr->beg+n;
	if(nn > hptr->last) {
		nbytes += nn - hptr->last;
		if(nbytes > maxsize)
			maxsize = nbytes;
		lbytes += nn - hptr->last;
		if(n > longest)
			longest = n;
/*		free(hptr->beg); /**/
		p = realloc(hptr->beg, n);
		if(p == 0) {
/*			hptr->beg = realloc(hptr->beg, hptr->last-hptr->beg);
**			garbage("seekc");
**			if((p = realloc(hptr->beg, n)) == 0)
*/				ospace("seekc");
		}
		hptr->beg = p;
		hptr->wt = hptr->last = hptr->rd = p+n;
		return;
	}
	hptr->rd = nn;
	if(nn>hptr->wt)
		hptr->wt = nn;
}

void
salterwd(Blk *ahptr, Blk *n)
{
	Wblk *hptr;

	hptr = (Wblk*)ahptr;
	if(hptr->rdw == hptr->lastw)
		more(ahptr);
	*hptr->rdw++ = n;
	if(hptr->rdw > hptr->wtw)
		hptr->wtw = hptr->rdw;
}

void
more(Blk *hptr)
{
	unsigned size;
	char *p;

	if((size=(hptr->last-hptr->beg)*2) == 0)
		size=2;
	nbytes += size/2;
	if(nbytes > maxsize)
		maxsize = nbytes;
	if(size > longest)
		longest = size;
	lbytes += size/2;
	lmore++;
/*	free(hptr->beg);/**/
	p = realloc(hptr->beg, size);

	if(p == 0) {
/*		hptr->beg = realloc(hptr->beg, (hptr->last-hptr->beg));
**		garbage("more");
**		if((p = realloc(hptr->beg,size)) == 0)
*/			ospace("more");
	}
	hptr->rd = p + (hptr->rd - hptr->beg);
	hptr->wt = p + (hptr->wt - hptr->beg);
	hptr->beg = p;
	hptr->last = p+size;
}

void
ospace(char *s)
{
	Bprint(&bout,"out of space: %s\n",s);
	Bprint(&bout,"all %ld rel %ld headmor %ld\n",all,rel,headmor);
	Bprint(&bout,"nbytes %ld\n",nbytes);
	sdump("stk",*stkptr);
	abort();
}

void
garbage(char *s)
{
	USED(s);
}

void
release(Blk *p)
{
	rel++;
	lrel++;
	nbytes -= p->last - p->beg;
	p->rd = (char*)hfree;
	hfree = p;
	free(p->beg);
}

Blk*
dcgetwd(Blk *p)
{
	Wblk *wp;

	wp = (Wblk*)p;
	if(wp->rdw == wp->wtw)
		return(0);
	return(*wp->rdw++);
}

void
putwd(Blk *p, Blk *c)
{
	Wblk *wp;

	wp = (Wblk*)p;
	if(wp->wtw == wp->lastw)
		more(p);
	*wp->wtw++ = c;
}

Blk*
lookwd(Blk *p)
{
	Wblk *wp;

	wp = (Wblk*)p;
	if(wp->rdw == wp->wtw)
		return(0);
	return(*wp->rdw);
}

char*
nalloc(char *p, unsigned nbytes)
{
	char *q, *r;

	q = r = malloc(nbytes);
	if(q==0)
		return(0);
	while(nbytes--)
		*q++ = *p++;
	return(r);
}

int
getstk(void)
{
	int n;
	uchar c;

	c = readc();
	if(c != '<')
		return c;
	n = 0;
	while(1) {
		c = readc();
		if(c == '>')
			break;
		n = n*10+c-'0';
	}
	return n;
}