swt.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

				goto jackpot;
			break;
		}
		zwrite(&b, p, sf, st);
	}
	Bflush(&b);
	close(f);
	firstp = P;
	lastp = P;
}

void
zwrite(Biobuf *b, Prog *p, int sf, int st)
{
	long l;

	l = p->as;
	Bputc(b, l);
	Bputc(b, l>>8);
	l = p->lineno;
	Bputc(b, l);
	Bputc(b, l>>8);
	Bputc(b, l>>16);
	Bputc(b, l>>24);
	zaddr(b, &p->from, sf);
	zaddr(b, &p->to, st);
}

void
zname(Biobuf *b, Sym *s, int t)
{
	char *n;
	ulong sig;

	if(debug['T'] && t == D_EXTERN && s->sig != SIGDONE && s->type != types[TENUM] && s != symrathole){
		sig = sign(s);
		Bputc(b, ASIGNAME);
		Bputc(b, ASIGNAME>>8);
		Bputc(b, sig);
		Bputc(b, sig>>8);
		Bputc(b, sig>>16);
		Bputc(b, sig>>24);
		s->sig = SIGDONE;
	}
	else{
		Bputc(b, ANAME);	/* as */
		Bputc(b, ANAME>>8);	/* as */
	}
	Bputc(b, t);		/* type */
	Bputc(b, s->sym);		/* sym */
	n = s->name;
	while(*n) {
		Bputc(b, *n);
		n++;
	}
	Bputc(b, 0);
}

void
zaddr(Biobuf *b, Adr *a, int s)
{
	long l;
	int i, t;
	char *n;
	Ieee e;

	t = 0;
	if(a->field)
		t |= T_FIELD;
	if(s)
		t |= T_SYM;

	switch(a->type) {
	default:
		if(a->offset)
			t |= T_OFFSET;
		if(a->displace)
			t |= T_INDEX;
		if(a->type & ~0xff)
			t |= T_TYPE;
		break;
	case D_FCONST:
		t |= T_FCONST;
		break;
	case D_SCONST:
		t |= T_SCONST;
		break;
	}
	Bputc(b, t);

	if(t & T_FIELD) {	/* implies field */
		i = a->field;
		Bputc(b, i);
		Bputc(b, i>>8);
	}
	if(t & T_INDEX) {	/* implies index, scale, displace */
		i = D_NONE;
		Bputc(b, i);
		Bputc(b, i>>8);
		Bputc(b, 0);
		l = a->displace;
		Bputc(b, l);
		Bputc(b, l>>8);
		Bputc(b, l>>16);
		Bputc(b, l>>24);
	}
	if(t & T_OFFSET) {	/* implies offset */
		l = a->offset;
		Bputc(b, l);
		Bputc(b, l>>8);
		Bputc(b, l>>16);
		Bputc(b, l>>24);
	}
	if(t & T_SYM)		/* implies sym */
		Bputc(b, s);
	if(t & T_FCONST) {
		ieeedtod(&e, a->dval);
		l = e.l;
		Bputc(b, l);
		Bputc(b, l>>8);
		Bputc(b, l>>16);
		Bputc(b, l>>24);
		l = e.h;
		Bputc(b, l);
		Bputc(b, l>>8);
		Bputc(b, l>>16);
		Bputc(b, l>>24);
		return;
	}
	if(t & T_SCONST) {
		n = a->sval;
		for(i=0; i<NSNAME; i++) {
			Bputc(b, *n);
			n++;
		}
		return;
	}
	i = a->type;
	Bputc(b, i);
	if(t & T_TYPE)
		Bputc(b, i>>8);
}



void
outhist(Biobuf *b)
{
	Hist *h;
	char *p, *q, *op, c;
	Prog pg;
	int n;

	pg = zprog;
	pg.as = AHISTORY;
	c = pathchar();
	for(h = hist; h != H; h = h->link) {
		p = h->name;
		op = 0;
		/* on windows skip drive specifier in pathname */
		if(systemtype(Windows) && p && p[1] == ':'){
			p += 2;
			c = *p;
		}
		if(p && p[0] != c && h->offset == 0 && pathname){
			/* on windows skip drive specifier in pathname */
			if(systemtype(Windows) && pathname[1] == ':') {
				op = p;
				p = pathname+2;
				c = *p;
			} else if(pathname[0] == c){
				op = p;
				p = pathname;
			}
		}
		while(p) {
			q = utfrune(p, c);
			if(q) {
				n = q-p;
				if(n == 0){
					n = 1;	/* leading "/" */
					*p = '/';	/* don't emit "\" on windows */
				}
				q++;
			} else {
				n = strlen(p);
				q = 0;
			}
			if(n) {
				Bputc(b, ANAME);
				Bputc(b, ANAME>>8);
				Bputc(b, D_FILE);
				Bputc(b, 1);
				Bputc(b, '<');
				Bwrite(b, p, n);
				Bputc(b, 0);
			}
			p = q;
			if(p == 0 && op) {
				p = op;
				op = 0;
			}
		}
		pg.lineno = h->line;
		pg.to.type = zprog.to.type;
		pg.to.offset = h->offset;
		if(h->offset)
			pg.to.type = D_CONST;

		zwrite(b, &pg, 0, 0);
	}
}

void
ieeedtod(Ieee *ieee, double native)
{
	double fr, ho, f;
	int exp;

	if(native < 0) {
		ieeedtod(ieee, -native);
		ieee->h |= 0x80000000L;
		return;
	}
	if(native == 0) {
		ieee->l = 0;
		ieee->h = 0;
		return;
	}
	fr = frexp(native, &exp);
	f = 2097152L;		/* shouldnt use fp constants here */
	fr = modf(fr*f, &ho);
	ieee->h = ho;
	ieee->h &= 0xfffffL;
	ieee->h |= (exp+1022L) << 20;
	f = 65536L;
	fr = modf(fr*f, &ho);
	ieee->l = ho;
	ieee->l <<= 16;
	ieee->l |= (long)(fr*f);
}

int
nodalloc(Type *t, int g, Node *n)
{

	n->type = t;
	n->op = OREGISTER;
	n->addable = 12;
	n->complex = 0;
	g = regaddr(g);
	n->reg = g | I_INDIR;
	n->xoffset = 0;
	return g;
}

int
mulcon(Node *n, Node *c, int result, Node *nn)
{
	long v;

	if(typefd[n->type->etype])
		return 0;
	v = c->vconst;
	if(mulcon1(n, v, result, nn))
		return 1;
	return 0;
}

int
shlcon(Node *n, Node *c, int result, Node *nn)
{
	long v;

	v = 1L << c->vconst;
	return mulcon1(n, v, result, nn);
}

int
mulcon1(Node *n, long v, int result, Node *nn)
{
	int g, g1, a1, a2, neg;
	int o;
	char code[10], *p;

	if(result == D_NONE)
		return 0;
	neg = 0;
	if(v < 0) {
		v = -v;
		neg++;
	}
	a1 = 0;
	a2 = multabsize;
	for(;;) {
		if(a1 >= a2)
			return 0;
		g1 = (a2 + a1)/2;
		if(v < multab[g1].val) {
			a2 = g1;
			continue;
		}
		if(v > multab[g1].val) {
			a1 = g1+1;
			continue;
		}
		break;
	}
	strcpy(code, "0");
	strncat(code, multab[g1].code, sizeof(multab[0].code));
	p = code;
	if(p[1] == 'i')
		p += 2;
	g = regalloc(n->type, result);
	cgen(n, g, n);
	if(neg)
		gopcode(ONEG, n->type, D_NONE, n, g, n);
	g1 = regalloc(n->type, D_NONE);
loop:
	switch(*p) {
	case 0:
		regfree(g1);
		gmove(n->type, nn->type, g, n, result, nn);
		regfree(g);
		return 1;
	case '0':
		o = OAS;
		*p -= '0';
		goto com;
	case '1':
	case '2':
		o = OSUB;
		*p -= '1';
		goto com;
	case '3':
	case '4':
	case '5':
	case '6':
		o = OADD;
		*p -= '3';
	com:
		a1 = g;
		if(*p == 1 || *p == 3)
			a1 = g1;
		a2 = g;
		if(*p == 0 || *p == 3)
			a2 = g1;
		gopcode(o, n->type, a1, n, a2, n);
		p++;
		break;
	default:
		a1 = *p++ - 'a' + 1;
		a2 = g;
		if(a1 > 8) {
			a2 = g1;
			a1 -= 8;
		}
		gopcode(OASHL, n->type, D_CONST, nodconst(a1), a2, n);
		break;
	}
	goto loop;
}

void
nullwarn(Node *l, Node *r)
{
	warn(Z, "result of operation not used");
	if(l != Z)
		cgen(l, D_NONE, Z);
	if(r != Z)
		cgen(r, D_NONE, Z);
}

void
sextern(Sym *s, Node *a, long o, long w)
{
	long e, lw;

	for(e=0; e<w; e+=NSNAME) {
		lw = NSNAME;
		if(w-e < lw)
			lw = w-e;
		gpseudo(ADATA, s, D_SCONST, 0L);
		p->from.offset += o+e;
		p->from.displace = lw;
		memmove(p->to.sval, a->cstring+e, lw);
	}
}

void
gextern(Sym *s, Node *a, long o, long w)
{
	if(a->op == OCONST && typev[a->type->etype]) {
		gpseudo(ADATA, s, D_CONST, (long)(a->vconst>>32));
		p->from.offset += o;
		p->from.displace = 4;
		gpseudo(ADATA, s, D_CONST, (long)(a->vconst));
		p->from.offset += o + 4;
		p->from.displace = 4;
		return;
	}
	gpseudotree(ADATA, s, a);
	p->from.offset += o;
	p->from.displace = w;
}

long
align(long i, Type *t, int op)
{
	long o;
	Type *v;
	int w;

	o = i;
	w = 1;
	switch(op) {
	default:
		diag(Z, "unknown align opcode %d", op);
		break;

	case Asu2:	/* padding at end of a struct */
		w = SZ_LONG;
		if(packflg)
			w = packflg;
		break;

	case Ael1:	/* initial allign of struct element */
		for(v=t; v->etype==TARRAY; v=v->link)
			;
		w = ewidth[v->etype];
		if(w <= 0 || w >= SZ_SHORT)
			w = SZ_SHORT;
		if(packflg)
			w = packflg;
		break;

	case Ael2:	/* width of a struct element */
		o += t->width;
		break;

	case Aarg0:	/* initial passbyptr argument in arg list */
		if(typesuv[t->etype]) {
			o = align(o, types[TIND], Aarg1);
			o = align(o, types[TIND], Aarg2);
		}
		break;

	case Aarg1:	/* initial allign of parameter */
		w = ewidth[t->etype];
		if(w <= 0 || w >= SZ_LONG) {
			w = SZ_LONG;
			break;
		}
		o += SZ_LONG - w;	/* big endian adjustment */
		w = 1;
		break;

	case Aarg2:	/* width of a parameter */
		o += t->width;
		w = SZ_LONG;
		break;

	case Aaut3:	/* total allign of automatic */
		o = align(o, t, Ael1);
		o = align(o, t, Ael2);
		break;
	}
	o = round(o, w);
	if(debug['A'])
		print("align %s %ld %T = %ld\n", bnames[op], i, t, o);
	return o;
}

long
maxround(long max, long v)
{
	v += SZ_LONG-1;
	if(v > max)
		max = round(v, SZ_LONG);
	return max;
}