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

#include "gc.h"

int
swcmp(const void *a1, const void *a2)
{
	C1 *p1, *p2;

	p1 = (C1*)a1;
	p2 = (C1*)a2;
	if(p1->val < p2->val)
		return -1;
	return p1->val > p2->val;
}

void
doswit(int g, Node *n)
{
	Case *c;
	C1 *q, *iq;
	long def, nc, i;

	def = 0;
	nc = 0;
	for(c = cases; c->link != C; c = c->link) {
		if(c->def) {
			if(def)
				diag(n, "more than one default in switch");
			def = c->label;
			continue;
		}
		nc++;
	}

	iq = alloc(nc*sizeof(C1));
	q = iq;
	for(c = cases; c->link != C; c = c->link) {
		if(c->def)
			continue;
		q->label = c->label;
		q->val = c->val;
		q++;
	}
	qsort(iq, nc, sizeof(C1), swcmp);
	if(def == 0)
		def = breakpc;
	for(i=0; i<nc-1; i++)
		if(iq[i].val == iq[i+1].val)
			diag(n, "duplicate cases in switch %ld", iq[i].val);
	swit1(iq, nc, def, g, n);
}

#define	N1	4	/* ncase: always linear */
			/* else binary */
void
swit1(C1 *q, int nc, long def, int g, Node *n)
{
	C1 *r;
	int i;
	long v;
	Prog *sp1, *sp2;

	/* note that g and g+1 are not allocated */
	if(nc <= N1)
		goto linear;

	/*
	 * divide and conquer
	 */
	i = nc / 2;
	r = q+i;
	v = r->val;
	/* compare median */
	if(v >= -128 && v < 128) {
		gopcode(OAS, n->type, D_CONST, nodconst(v), g+1, n);
		gopcode(OEQ, n->type, g, n, g+1, n);
	} else
		gopcode(OEQ, n->type, g, n, D_CONST, nodconst(v));
	gbranch(OLT);
	sp1 = p;
	gbranch(OGT);
	sp2 = p;
	gbranch(OGOTO);
	patch(p, r->label);

	patch(sp1, pc);
	swit1(q, i, def, g, n);

	patch(sp2, pc);
	swit1(r+1, nc-i-1, def, g, n);
	return;

linear:
	for(i=0; i<nc; i++) {
		v = q->val;
		if(v >= -128 && v < 128) {
			gopcode(OAS, n->type, D_CONST, nodconst(v), g+1, n);
			gopcode(OEQ, n->type, g+1, n, g, n);
		} else
			gopcode(OEQ, n->type, g, n, D_CONST, nodconst(v));
		gbranch(OEQ);
		patch(p, q->label);
		q++;
	}
	gbranch(OGOTO);
	patch(p, def);
}

void
cas(void)
{
	Case *c;

	c = alloc(sizeof(*c));
	c->link = cases;
	cases = c;
}


int
bitload(Node *b, int n1, int n2, int n3, Node *nn)
{
	int sh, g, gs;
	long v;
	Node *l;
	Type *t;

	/*
	 * n1 gets adjusted/masked value
	 * n2 gets address of cell
	 * n3 gets contents of cell
	 */
	gs = 0;
	t = tfield;

	l = b->left;
	g = regalloc(t, n3);
	if(n2 != D_NONE) {
		lcgen(l, n2, Z);
		n2 |= I_INDIR;
		gmove(t, t, n2, l, g, l);
		gmove(t, t, g, l, n1, l);
	} else
		cgen(l, g, nn);
	if(b->type->shift == 0 && typeu[b->type->etype]) {
		v = ~0 + (1L << b->type->nbits);
		gopcode(OAND, t, D_CONST, nodconst(v), g, l);
	} else {
		sh = 32 - b->type->shift - b->type->nbits;
		if(sh > 0)
			if(sh >= 8) {
				gs = regalloc(t, D_NONE);
				gmove(t, t, D_CONST, nodconst(sh), gs, l);
				gopcode(OASHL, t, gs, l, g, l);
				if(b->type->shift)
					regfree(gs);
			} else
				gopcode(OASHL, t, D_CONST, nodconst(sh), g, l);
		sh += b->type->shift;
		if(sh > 0) {
			if(sh >= 8) {
				if(b->type->shift) {
					gs = regalloc(t, D_NONE);
					gmove(t, t, D_CONST, nodconst(sh), gs, l);
				}
				if(typeu[b->type->etype])
					gopcode(OLSHR, t, gs, l, g, l);
				else
					gopcode(OASHR, t, gs, l, g, l);
				regfree(gs);
			} else {
				if(typeu[b->type->etype])
					gopcode(OLSHR, t, D_CONST, nodconst(sh), g, l);
				else
					gopcode(OASHR, t, D_CONST, nodconst(sh), g, l);
			}
		}
	}
	return g;
}

void
bitstore(Node *b, int n1, int n2, int n3, int result, Node *nn)
{
	long v;
	Node *l;
	Type *t;
	int sh, g, gs;

	/*
	 * n1 has adjusted/masked value
	 * n2 has address of cell
	 * n3 has contents of cell
	 */
	t = tfield;

	l = b->left;
	g = regalloc(t, D_NONE);
	v = ~0 + (1L << b->type->nbits);
	gopcode(OAND, t, D_CONST, nodconst(v), n1, l);
	gmove(t, t, n1, l, g, l);
	if(result != D_NONE)
		gmove(t, nn->type, n1, l, result, nn);
	sh = b->type->shift;
	if(sh > 0) {
		if(sh >= 8) {
			gs = regalloc(t, D_NONE);
			gmove(t, t, D_CONST, nodconst(sh), gs, l);
			gopcode(OASHL, t, gs, l, g, l);
			regfree(gs);
		} else
			gopcode(OASHL, t, D_CONST, nodconst(sh), g, l);
	}
	v <<= sh;
	gopcode(OAND, t, D_CONST, nodconst(~v), n3, l);
	gopcode(OOR, t, n3, l, g, l);
	gmove(t, t, g, l, n2|I_INDIR, l);

	regfree(g);
	regfree(n1);
	regfree(n2);
	regfree(n3);
}

long
outstring(char *s, long n)
{
	long r;

	r = nstring;
	while(n) {
		string[mnstring] = *s++;
		mnstring++;
		nstring++;
		if(mnstring >= NSNAME) {
			gpseudo(ADATA, symstring, D_SCONST, 0L);
			memmove(p->to.sval, string, NSNAME);
			p->from.offset = nstring - NSNAME;
			p->from.displace = NSNAME;
			mnstring = 0;
		}
		n--;
	}
	return r;
}

long
outlstring(ushort *s, long n)
{
	char buf[2];
	int c;
	long r;

	while(nstring & 1)
		outstring("", 1);
	r = nstring;
	while(n > 0) {
		c = *s++;
		if(align(0, types[TCHAR], Aarg1)) {
			buf[0] = c>>8;
			buf[1] = c;
		} else {
			buf[0] = c;
			buf[1] = c>>8;
		}
		outstring(buf, 2);
		n -= sizeof(ushort);
	}
	return r;
}

int
doinc(Node *n, int f)
{
	Node *l;
	int a;

loop:
	if(n == Z)
		return 0;
	l = n->left;
	switch(n->op) {

	case OPOSTINC:
	case OPOSTDEC:
		if(f & POST) {
			a = n->addable;
			if(a >= INDEXED) {
				if(f & TEST)
					return 1;
				n->addable = 0;
				cgen(n, D_NONE, n);
				n->addable = a;
			}
		}
		break;

	case OAS:
	case OASLMUL:
	case OASLDIV:
	case OASLMOD:
	case OASMUL:
	case OASDIV:
	case OASMOD:
	case OASXOR:
	case OASOR:
	case OASADD:
	case OASSUB:
	case OASLSHR:
	case OASASHR:
	case OASASHL:
	case OASAND:

	case OPREINC:
	case OPREDEC:
		if(f & PRE) {
			a = n->addable;
			if(a >= INDEXED) {
				if(f & TEST)
					return 1;
				n->addable = 0;
				doinc(n, PRE);
				cgen(n, D_NONE, n);
				n->addable = a;
				return 0;
			}
		}
		break;

	case OFUNC:
		if(f & PRE)
			break;
		return 0;

	case ONAME:
	case OREGISTER:
	case OSTRING:
	case OCONST:

	case OANDAND:
	case OOROR:
		return 0;

	case OCOND:
		return 0;

	case OCOMMA:
		n = n->right;
		if(f & PRE)
			n = l;
		goto loop;
	}
	if(l != Z)
		if(doinc(l, f))
			return 1;
	n = n->right;
	goto loop;
}

void
setsp(void)
{

	nextpc();
	p->as = AADJSP;
	p->from.type = D_CONST;
	p->from.offset = 0;
}

void
adjsp(long o)
{

	if(o != 0) {
		nextpc();
		p->as = AADJSP;
		p->from.type = D_CONST;
		p->from.offset = o;
		argoff += o;
	}
}

int
simplv(Node *n)
{

	if(n->addable <= INDEXED)
		return 0;
	while(n->op == OIND)
		n = n->left;
	if(n->op == ONAME)
		return 1;
	return 0;
}

int
eval(Node *n, int g)
{

	if(n->addable >= INDEXED)
		return D_TREE;
	g = regalloc(n->type, g);
	cgen(n, g, n);
	return g;
}

void	outhist(Biobuf*);
void	zname(Biobuf*, Sym*, int);
void	zaddr(Biobuf*, Adr*, int);
void	zwrite(Biobuf*, Prog*, int, int);

void
outcode(void)
{
	struct { Sym *sym; short type; } h[NSYM];
	Prog *p;
	Sym *s;
	int f, sf, st, t, sym;
	Biobuf b;

	if(debug['S']) {
		for(p = firstp; p != P; p = p->link)
			if(p->as != ADATA && p->as != AGLOBL)
				pc--;
		for(p = firstp; p != P; p = p->link) {
			print("%P\n", p);
			if(p->as != ADATA && p->as != AGLOBL)
				pc++;
		}
	}
	f = open(outfile, OWRITE);
	if(f < 0) {
		diag(Z, "cant open %s", outfile);
		errorexit();
	}
	Binit(&b, f, OWRITE);
	Bseek(&b, 0L, 2);
	outhist(&b);
	for(sym=0; sym<NSYM; sym++) {
		h[sym].sym = S;
		h[sym].type = 0;
	}
	sym = 1;
	for(p = firstp; p != P; p = p->link) {
	jackpot:
		sf = 0;
		s = p->from.sym;
		while(s != S) {
			sf = s->sym;
			if(sf < 0 || sf >= NSYM)
				sf = 0;
			t = p->from.type & D_MASK;
			if(h[sf].type == t)
			if(h[sf].sym == s)
				break;
			s->sym = sym;
			zname(&b, s, t);
			h[sym].sym = s;
			h[sym].type = t;
			sf = sym;
			sym++;
			if(sym >= NSYM)
				sym = 1;
			break;
		}
		st = 0;
		s = p->to.sym;
		while(s != S) {
			st = s->sym;
			if(st < 0 || st >= NSYM)
				st = 0;
			t = p->to.type & D_MASK;
			if(h[st].type == t)
			if(h[st].sym == s)
				break;
			s->sym = sym;
			zname(&b, s, t);
			h[sym].sym = s;
			h[sym].type = t;
			st = sym;
			sym++;
			if(sym >= NSYM)
				sym = 1;
			if(st == sf)