cpython/Python/ceval.c

/* Execute compiled code */

#include "allobjects.h"

#include "import.h"
#include "sysmodule.h"
#include "compile.h"
#include "frameobject.h"
#include "ceval.h"
#include "opcode.h"
#include "builtinmodule.h"
#include "traceback.h"

#ifndef NDEBUG
#define TRACE
#endif

#ifdef TRACE
static int
prtrace(v, str)
	object *v;
	char *str;
{
	printf("%s ", str);
	printobject(v, stdout, 0);
	printf("\n");
}
#endif

static frameobject *current_frame;

object *
getlocals()
{
	if (current_frame == NULL)
		return NULL;
	else
		return current_frame->f_locals;
}

object *
getglobals()
{
	if (current_frame == NULL)
		return NULL;
	else
		return current_frame->f_globals;
}

void
printtraceback(fp)
	FILE *fp;
{
	object *v = tb_fetch();
	if (v != NULL) {
		fprintf(fp, "Stack backtrace (innermost last):\n");
		tb_print(v, fp);
		DECREF(v);
	}
}


/* XXX Mixing "print ...," and direct file I/O on stdin/stdout
   XXX has some bad consequences.  The needspace flag should
   XXX really be part of the file object. */

static int needspace;

void
flushline()
{
	FILE *fp = sysgetfile("stdout", stdout);
	if (needspace) {
		fprintf(fp, "\n");
		needspace = 0;
	}
}


/* Test a value used as condition, e.g., in a for or if statement */

static int
testbool(v)
	object *v;
{
	if (is_intobject(v))
		return getintvalue(v) != 0;
	if (is_floatobject(v))
		return getfloatvalue(v) != 0.0;
	if (v->ob_type->tp_as_sequence != NULL)
		return (*v->ob_type->tp_as_sequence->sq_length)(v) != 0;
	if (v->ob_type->tp_as_mapping != NULL)
		return (*v->ob_type->tp_as_mapping->mp_length)(v) != 0;
	if (v == None)
		return 0;
	/* All other objects are 'true' */
	return 1;
}

static object *
add(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL)
		v = (*v->ob_type->tp_as_number->nb_add)(v, w);
	else if (v->ob_type->tp_as_sequence != NULL)
		v = (*v->ob_type->tp_as_sequence->sq_concat)(v, w);
	else {
		err_setstr(TypeError, "+ not supported by operands");
		return NULL;
	}
	return v;
}

static object *
sub(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL)
		return (*v->ob_type->tp_as_number->nb_subtract)(v, w);
	err_setstr(TypeError, "bad operand type(s) for -");
	return NULL;
}

static object *
mul(v, w)
	object *v, *w;
{
	typeobject *tp;
	if (is_intobject(v) && w->ob_type->tp_as_sequence != NULL) {
		/* int*sequence -- swap v and w */
		object *tmp = v;
		v = w;
		w = tmp;
	}
	tp = v->ob_type;
	if (tp->tp_as_number != NULL)
		return (*tp->tp_as_number->nb_multiply)(v, w);
	if (tp->tp_as_sequence != NULL) {
		if (!is_intobject(w)) {
			err_setstr(TypeError,
				"can't multiply sequence with non-int");
			return NULL;
		}
		if (tp->tp_as_sequence->sq_repeat == NULL) {
			err_setstr(TypeError, "sequence does not support *");
			return NULL;
		}
		return (*tp->tp_as_sequence->sq_repeat)
						(v, (int)getintvalue(w));
	}
	err_setstr(TypeError, "bad operand type(s) for *");
	return NULL;
}

static object *
div(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL)
		return (*v->ob_type->tp_as_number->nb_divide)(v, w);
	err_setstr(TypeError, "bad operand type(s) for /");
	return NULL;
}

static object *
rem(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL)
		return (*v->ob_type->tp_as_number->nb_remainder)(v, w);
	err_setstr(TypeError, "bad operand type(s) for %");
	return NULL;
}

static object *
neg(v)
	object *v;
{
	if (v->ob_type->tp_as_number != NULL)
		return (*v->ob_type->tp_as_number->nb_negative)(v);
	err_setstr(TypeError, "bad operand type(s) for unary -");
	return NULL;
}

static object *
pos(v)
	object *v;
{
	if (v->ob_type->tp_as_number != NULL)
		return (*v->ob_type->tp_as_number->nb_positive)(v);
	err_setstr(TypeError, "bad operand type(s) for unary +");
	return NULL;
}

static object *
not(v)
	object *v;
{
	int outcome = testbool(v);
	object *w = outcome == 0 ? True : False;
	INCREF(w);
	return w;
}

static object *
call_builtin(func, arg)
	object *func;
	object *arg;
{
	if (is_methodobject(func)) {
		method meth = getmethod(func);
		object *self = getself(func);
		return (*meth)(self, arg);
	}
	if (is_classobject(func)) {
		if (arg != NULL) {
			err_setstr(TypeError,
				"classobject() allows no arguments");
			return NULL;
		}
		return newclassmemberobject(func);
	}
	err_setstr(TypeError, "call of non-function");
	return NULL;
}

static object *
call_function(func, arg)
	object *func;
	object *arg;
{
	object *newarg = NULL;
	object *newlocals, *newglobals;
	object *co, *v;
	
	if (is_classmethodobject(func)) {
		object *self = classmethodgetself(func);
		func = classmethodgetfunc(func);
		if (arg == NULL) {
			arg = self;
		}
		else {
			newarg = newtupleobject(2);
			if (newarg == NULL)
				return NULL;
			INCREF(self);
			INCREF(arg);
			settupleitem(newarg, 0, self);
			settupleitem(newarg, 1, arg);
			arg = newarg;
		}
	}
	else {
		if (!is_funcobject(func)) {
			err_setstr(TypeError, "call of non-function");
			return NULL;
		}
	}
	
	co = getfunccode(func);
	if (co == NULL) {
		XDECREF(newarg);
		return NULL;
	}
	if (!is_codeobject(co)) {
		fprintf(stderr, "XXX Bad code\n");
		abort();
	}
	newlocals = newdictobject();
	if (newlocals == NULL) {
		XDECREF(newarg);
		return NULL;
	}
	
	newglobals = getfuncglobals(func);
	INCREF(newglobals);
	
	v = eval_code((codeobject *)co, newglobals, newlocals, arg);
	
	DECREF(newlocals);
	DECREF(newglobals);
	
	XDECREF(newarg);
	
	return v;
}

static object *
apply_subscript(v, w)
	object *v, *w;
{
	typeobject *tp = v->ob_type;
	if (tp->tp_as_sequence == NULL && tp->tp_as_mapping == NULL) {
		err_setstr(TypeError, "unsubscriptable object");
		return NULL;
	}
	if (tp->tp_as_sequence != NULL) {
		int i;
		if (!is_intobject(w)) {
			err_setstr(TypeError, "sequence subscript not int");
			return NULL;
		}
		i = getintvalue(w);
		return (*tp->tp_as_sequence->sq_item)(v, i);
	}
	return (*tp->tp_as_mapping->mp_subscript)(v, w);
}

static object *
loop_subscript(v, w)
	object *v, *w;
{
	sequence_methods *sq = v->ob_type->tp_as_sequence;
	int i, n;
	if (sq == NULL) {
		err_setstr(TypeError, "loop over non-sequence");
		return NULL;
	}
	i = getintvalue(w);
	n = (*sq->sq_length)(v);
	if (i >= n)
		return NULL; /* End of loop */
	return (*sq->sq_item)(v, i);
}

static int
slice_index(v, isize, pi)
	object *v;
	int isize;
	int *pi;
{
	if (v != NULL) {
		if (!is_intobject(v)) {
			err_setstr(TypeError, "slice index must be int");
			return -1;
		}
		*pi = getintvalue(v);
		if (*pi < 0)
			*pi += isize;
	}
	return 0;
}

static object *
apply_slice(u, v, w) /* return u[v:w] */
	object *u, *v, *w;
{
	typeobject *tp = u->ob_type;
	int ilow, ihigh, isize;
	if (tp->tp_as_sequence == NULL) {
		err_setstr(TypeError, "only sequences can be sliced");
		return NULL;
	}
	ilow = 0;
	isize = ihigh = (*tp->tp_as_sequence->sq_length)(u);
	if (slice_index(v, isize, &ilow) != 0)
		return NULL;
	if (slice_index(w, isize, &ihigh) != 0)
		return NULL;
	return (*tp->tp_as_sequence->sq_slice)(u, ilow, ihigh);
}

static int
assign_subscript(w, key, v) /* w[key] = v */
	object *w;
	object *key;
	object *v;
{
	typeobject *tp = w->ob_type;
	sequence_methods *sq;
	mapping_methods *mp;
	int (*func)();
	if ((sq = tp->tp_as_sequence) != NULL &&
			(func = sq->sq_ass_item) != NULL) {
		if (!is_intobject(key)) {
			err_setstr(TypeError,
				"sequence subscript must be integer");
			return -1;
		}
		else
			return (*func)(w, (int)getintvalue(key), v);
	}
	else if ((mp = tp->tp_as_mapping) != NULL &&
			(func = mp->mp_ass_subscript) != NULL) {
		return (*func)(w, key, v);
	}
	else {
		err_setstr(TypeError,
				"can't assign to this subscripted object");
		return -1;
	}
}

static int
assign_slice(u, v, w, x) /* u[v:w] = x */
	object *u, *v, *w, *x;
{
	sequence_methods *sq = u->ob_type->tp_as_sequence;
	int ilow, ihigh, isize;
	if (sq == NULL) {
		err_setstr(TypeError, "assign to slice of non-sequence");
		return -1;
	}
	if (sq == NULL || sq->sq_ass_slice == NULL) {
		err_setstr(TypeError, "unassignable slice");
		return -1;
	}
	ilow = 0;
	isize = ihigh = (*sq->sq_length)(u);
	if (slice_index(v, isize, &ilow) != 0)
		return -1;
	if (slice_index(w, isize, &ihigh) != 0)
		return -1;
	return (*sq->sq_ass_slice)(u, ilow, ihigh, x);
}

static int
cmp_exception(err, v)
	object *err, *v;
{
	if (is_tupleobject(v)) {
		int i, n;
		n = gettuplesize(v);
		for (i = 0; i < n; i++) {
			if (err == gettupleitem(v, i))
				return 1;
		}
		return 0;
	}
	return err == v;
}

static int
cmp_member(v, w)
	object *v, *w;
{
	int i, n, cmp;
	object *x;
	sequence_methods *sq;
	/* Special case for char in string */
	if (is_stringobject(w)) {
		register char *s, *end;
		register char c;
		if (!is_stringobject(v) || getstringsize(v) != 1) {
			err_setstr(TypeError,
			    "string member test needs char left operand");
			return -1;
		}
		c = getstringvalue(v)[0];
		s = getstringvalue(w);
		end = s + getstringsize(w);
		while (s < end) {
			if (c == *s++)
				return 1;
		}
		return 0;
	}
	sq = w->ob_type->tp_as_sequence;
	if (sq == NULL) {
		err_setstr(TypeError,
			"'in' or 'not in' needs sequence right argument");
		return -1;
	}
	n = (*sq->sq_length)(w);
	for (i = 0; i < n; i++) {
		x = (*sq->sq_item)(w, i);
		cmp = cmpobject(v, x);
		XDECREF(x);
		if (cmp == 0)
			return 1;
	}
	return 0;
}

static object *
cmp_outcome(op, v, w)
	enum cmp_op op;
	register object *v;
	register object *w;
{
	register int cmp;
	register int res = 0;
	switch (op) {
	case IS:
	case IS_NOT:
		res = (v == w);
		if (op == IS_NOT)
			res = !res;
		break;
	case IN:
	case NOT_IN:
		res = cmp_member(v, w);
		if (res < 0)
			return NULL;
		if (op == NOT_IN)
			res = !res;
		break;
	case EXC_MATCH:
		res = cmp_exception(v, w);
		break;
	default:
		cmp = cmpobject(v, w);
		switch (op) {
		case LT: res = cmp <  0; break;
		case LE: res = cmp <= 0; break;
		case EQ: res = cmp == 0; break;
		case NE: res = cmp != 0; break;
		case GT: res = cmp >  0; break;
		case GE: res = cmp >= 0; break;
		/* XXX no default? (res is initialized to 0 though) */
		}
	}
	v = res ? True : False;
	INCREF(v);
	return v;
}

static int
import_from(locals, v, name)
	object *locals;
	object *v;
	char *name;
{
	object *w, *x;
	w = getmoduledict(v);
	if (name[0] == '*') {
		int i;
		int n = getdictsize(w);
		for (i = 0; i < n; i++) {
			name = getdictkey(w, i);
			if (name == NULL || name[0] == '_')
				continue;
			x = dictlookup(w, name);
			if (x == NULL) {
				/* XXX can't happen? */
				err_setstr(NameError, name);
				return -1;
			}
			if (dictinsert(locals, name, x) != 0)
				return -1;
		}
		return 0;
	}
	else {
		x = dictlookup(w, name);
		if (x == NULL) {
			err_setstr(NameError, name);
			return -1;
		}
		else
			return dictinsert(locals, name, x);
	}
}

static object *
build_class(v, w)
	object *v; /* None or tuple containing base classes */
	object *w; /* dictionary */
{
	if (is_tupleobject(v)) {
		int i;
		for (i = gettuplesize(v); --i >= 0; ) {
			object *x = gettupleitem(v, i);
			if (!is_classobject(x)) {
				err_setstr(TypeError,
					"base is not a class object");
				return NULL;
			}
		}
	}
	else {
		v = NULL;
	}
	if (!is_dictobject(w)) {
		err_setstr(SystemError, "build_class with non-dictionary");
		return NULL;
	}
	return newclassobject(v, w);
}


/* Status code for main loop (reason for stack unwind) */

enum why_code {
		WHY_NOT,	/* No error */
		WHY_EXCEPTION,	/* Exception occurred */
		WHY_RERAISE,	/* Exception re-raised by 'finally' */
		WHY_RETURN,	/* 'return' statement */
		WHY_BREAK	/* 'break' statement */
};

/* Interpreter main loop */

object *
eval_code(co, globals, locals, arg)
	codeobject *co;
	object *globals;
	object *locals;
	object *arg;
{
	register unsigned char *next_instr;
	register int opcode;	/* Current opcode */
	register int oparg;	/* Current opcode argument, if any */
	register object **stack_pointer;
	register enum why_code why; /* Reason for block stack unwind */
	register int err;	/* Error status -- nonzero if error */
	register object *x;	/* Result object -- NULL if error */
	register object *v;	/* Temporary objects popped off stack */
	register object *w;
	register object *u;
	register object *t;
	register frameobject *f; /* Current frame */
	int lineno;		/* Current line number */
	object *retval;		/* Return value iff why == WHY_RETURN */
	char *name;		/* Name used by some instructions */
	FILE *fp;		/* Used by print operations */
#ifdef TRACE
	int trace = dictlookup(globals, "__trace__") != NULL;
#endif

/* Code access macros */

#define GETCONST(i)	Getconst(f, i)
#define GETNAME(i)	Getname(f, i)
#define FIRST_INSTR()	(GETUSTRINGVALUE(f->f_code->co_code))
#define INSTR_OFFSET()	(next_instr - FIRST_INSTR())
#define NEXTOP()	(*next_instr++)
#define NEXTARG()	(next_instr += 2, (next_instr[-1]<<8) + next_instr[-2])
#define JUMPTO(x)	(next_instr = FIRST_INSTR() + (x))
#define JUMPBY(x)	(next_instr += (x))

/* Stack manipulation macros */

#define STACK_LEVEL()	(stack_pointer - f->f_valuestack)
#define EMPTY()		(STACK_LEVEL() == 0)
#define TOP()		(stack_pointer[-1])
#define BASIC_PUSH(v)	(*stack_pointer++ = (v))
#define BASIC_POP()	(*--stack_pointer)

#ifdef TRACE
#define PUSH(v)		(BASIC_PUSH(v), trace && prtrace(TOP(), "push"))
#define POP()		(trace && prtrace(TOP(), "pop"), BASIC_POP())
#else
#define PUSH(v)		BASIC_PUSH(v)
#define POP()		BASIC_POP()
#endif

	f = newframeobject(
			current_frame,		/*back*/
			co,			/*code*/
			globals,		/*globals*/
			locals,			/*locals*/
			50,			/*nvalues*/
			20);			/*nblocks*/
	if (f == NULL)
		return NULL;
	
	current_frame = f;
	
	next_instr = GETUSTRINGVALUE(f->f_code->co_code);
	
	stack_pointer = f->f_valuestack;
	
	if (arg != NULL) {
		INCREF(arg);
		PUSH(arg);
	}
	
	why = WHY_NOT;
	err = 0;
	x = None;	/* Not a reference, just anything non-NULL */
	lineno = -1;
	
	for (;;) {
		static ticker;
		
		/* Do periodic things */
		
		if (--ticker < 0) {
			ticker = 100;
			if (intrcheck()) {
				err_set(KeyboardInterrupt);
				why = WHY_EXCEPTION;
				tb_here(f, INSTR_OFFSET(), lineno);
				break;
			}
		}
		
		/* Extract opcode and argument */
		
		opcode = NEXTOP();
		if (HAS_ARG(opcode))
			oparg = NEXTARG();

#ifdef TRACE
		/* Instruction tracing */
		
		if (trace) {
			if (HAS_ARG(opcode)) {
				printf("%d: %d, %d\n",
					(int) (INSTR_OFFSET() - 3),
					opcode, oparg);
			}
			else {
				printf("%d: %d\n",
					(int) (INSTR_OFFSET() - 1), opcode);
			}
		}
#endif

		/* Main switch on opcode */
		
		switch (opcode) {
		
		/* BEWARE!
		   It is essential that any operation that fails sets either
		   x to NULL, err to nonzero, or why to anything but WHY_NOT,
		   and that no operation that succeeds does this! */
		
		/* case STOP_CODE: this is an error! */
		
		case POP_TOP:
			v = POP();
			DECREF(v);
			break;
		
		case ROT_TWO:
			v = POP();
			w = POP();
			PUSH(v);
			PUSH(w);
			break;
		
		case ROT_THREE:
			v = POP();
			w = POP();
			x = POP();
			PUSH(v);
			PUSH(x);
			PUSH(w);
			break;
		
		case DUP_TOP:
			v = TOP();
			INCREF(v);
			PUSH(v);
			break;
		
		case UNARY_POSITIVE:
			v = POP();
			x = pos(v);
			DECREF(v);
			PUSH(x);
			break;
		
		case UNARY_NEGATIVE:
			v = POP();
			x = neg(v);
			DECREF(v);
			PUSH(x);
			break;
		
		case UNARY_NOT:
			v = POP();
			x = not(v);
			DECREF(v);
			PUSH(x);
			break;
		
		case UNARY_CONVERT:
			v = POP();
			x = reprobject(v);
			DECREF(v);
			PUSH(x);
			break;
		
		case UNARY_CALL:
			v = POP();
			if (is_classmethodobject(v) || is_funcobject(v))
				x = call_function(v, (object *)NULL);
			else
				x = call_builtin(v, (object *)NULL);
			DECREF(v);
			PUSH(x);
			break;
		
		case BINARY_MULTIPLY:
			w = POP();
			v = POP();
			x = mul(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_DIVIDE:
			w = POP();
			v = POP();
			x = div(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_MODULO:
			w = POP();
			v = POP();
			x = rem(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_ADD:
			w = POP();
			v = POP();
			x = add(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_SUBTRACT:
			w = POP();
			v = POP();
			x = sub(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_SUBSCR:
			w = POP();
			v = POP();
			x = apply_subscript(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_CALL:
			w = POP();
			v = POP();
			if (is_classmethodobject(v) || is_funcobject(v))
				x = call_function(v, w);
			else
				x = call_builtin(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case SLICE+0:
		case SLICE+1:
		case SLICE+2:
		case SLICE+3:
			if ((opcode-SLICE) & 2)
				w = POP();
			else
				w = NULL;
			if ((opcode-SLICE) & 1)
				v = POP();
			else
				v = NULL;
			u = POP();
			x = apply_slice(u, v, w);
			DECREF(u);
			XDECREF(v);
			XDECREF(w);
			PUSH(x);
			break;
		
		case STORE_SLICE+0:
		case STORE_SLICE+1:
		case STORE_SLICE+2:
		case STORE_SLICE+3:
			if ((opcode-STORE_SLICE) & 2)
				w = POP();
			else
				w = NULL;
			if ((opcode-STORE_SLICE) & 1)
				v = POP();
			else
				v = NULL;
			u = POP();
			t = POP();
			err = assign_slice(u, v, w, t); /* u[v:w] = t */
			DECREF(t);
			DECREF(u);
			XDECREF(v);
			XDECREF(w);
			break;
		
		case DELETE_SLICE+0:
		case DELETE_SLICE+1:
		case DELETE_SLICE+2:
		case DELETE_SLICE+3:
			if ((opcode-DELETE_SLICE) & 2)
				w = POP();
			else
				w = NULL;
			if ((opcode-DELETE_SLICE) & 1)
				v = POP();
			else
				v = NULL;
			u = POP();
			err = assign_slice(u, v, w, (object *)NULL);
							/* del u[v:w] */
			DECREF(u);
			XDECREF(v);
			XDECREF(w);
			break;
		
		case STORE_SUBSCR:
			w = POP();
			v = POP();
			u = POP();
			/* v[w] = u */
			err = assign_subscript(v, w, u);
			DECREF(u);
			DECREF(v);
			DECREF(w);
			break;
		
		case DELETE_SUBSCR:
			w = POP();
			v = POP();
			/* del v[w] */
			err = assign_subscript(v, w, (object *)NULL);
			DECREF(v);
			DECREF(w);
			break;
		
		case PRINT_EXPR:
			v = POP();
			fp = sysgetfile("stdout", stdout);
			/* Print value except if procedure result */
			if (v != None) {
				flushline();
				printobject(v, fp, 0);
				fprintf(fp, "\n");
			}
			DECREF(v);
			break;
		
		case PRINT_ITEM:
			v = POP();
			fp = sysgetfile("stdout", stdout);
			if (needspace)
				fprintf(fp, " ");
			if (is_stringobject(v)) {
				char *s = getstringvalue(v);
				int len = getstringsize(v);
				fwrite(s, 1, len, fp);
				if (len > 0 && s[len-1] == '\n')
					needspace = 0;
				else
					needspace = 1;
			}
			else {
				printobject(v, fp, 0);
				needspace = 1;
			}
			DECREF(v);
			break;
		
		case PRINT_NEWLINE:
			fp = sysgetfile("stdout", stdout);
			fprintf(fp, "\n");
			needspace = 0;
			break;
		
		case BREAK_LOOP:
			why = WHY_BREAK;
			break;
		
		case RAISE_EXCEPTION:
			v = POP();
			w = POP();
			if (!is_stringobject(w))
				err_setstr(TypeError,
					"exceptions must be strings");
			else
				err_setval(w, v);
			DECREF(v);
			DECREF(w);
			why = WHY_EXCEPTION;
			break;
		
		case LOAD_LOCALS:
			v = f->f_locals;
			INCREF(v);
			PUSH(v);
			break;
		
		case RETURN_VALUE:
			retval = POP();
			why = WHY_RETURN;
			break;
		
		case REQUIRE_ARGS:
			if (EMPTY()) {
				err_setstr(TypeError,
					"function expects argument(s)");
				why = WHY_EXCEPTION;
			}
			break;
		
		case REFUSE_ARGS:
			if (!EMPTY()) {
				err_setstr(TypeError,
					"function expects no argument(s)");
				why = WHY_EXCEPTION;
			}
			break;
		
		case BUILD_FUNCTION:
			v = POP();
			x = newfuncobject(v, f->f_globals);
			DECREF(v);
			PUSH(x);
			break;
		
		case POP_BLOCK:
			{
				block *b = pop_block(f);
				while (STACK_LEVEL() > b->b_level) {
					v = POP();
					DECREF(v);
				}
			}
			break;
		
		case END_FINALLY:
			v = POP();
			if (is_intobject(v)) {
				why = (enum why_code) getintvalue(v);
				if (why == WHY_RETURN)
					retval = POP();
			}
			else if (is_stringobject(v)) {
				w = POP();
				err_setval(v, w);
				DECREF(w);
				w = POP();
				tb_store(w);
				DECREF(w);
				why = WHY_RERAISE;
			}
			else if (v != None) {
				err_setstr(SystemError,
					"'finally' pops bad exception");
				why = WHY_EXCEPTION;
			}
			DECREF(v);
			break;
		
		case BUILD_CLASS:
			w = POP();
			v = POP();
			x = build_class(v, w);
			PUSH(x);
			DECREF(v);
			DECREF(w);
			break;
		
		case STORE_NAME:
			name = GETNAME(oparg);
			v = POP();
			err = dictinsert(f->f_locals, name, v);
			DECREF(v);
			break;
		
		case DELETE_NAME:
			name = GETNAME(oparg);
			if ((err = dictremove(f->f_locals, name)) != 0)
				err_setstr(NameError, name);
			break;
		
		case UNPACK_TUPLE:
			v = POP();
			if (!is_tupleobject(v)) {
				err_setstr(TypeError, "unpack non-tuple");
				why = WHY_EXCEPTION;
			}
			else if (gettuplesize(v) != oparg) {
				err_setstr(RuntimeError,
					"unpack tuple of wrong size");
				why = WHY_EXCEPTION;
			}
			else {
				for (; --oparg >= 0; ) {
					w = gettupleitem(v, oparg);
					INCREF(w);
					PUSH(w);
				}
			}
			DECREF(v);
			break;
		
		case UNPACK_LIST:
			v = POP();
			if (!is_listobject(v)) {
				err_setstr(TypeError, "unpack non-list");
				why = WHY_EXCEPTION;
			}
			else if (getlistsize(v) != oparg) {
				err_setstr(RuntimeError,
					"unpack list of wrong size");
				why = WHY_EXCEPTION;
			}
			else {
				for (; --oparg >= 0; ) {
					w = getlistitem(v, oparg);
					INCREF(w);
					PUSH(w);
				}
			}
			DECREF(v);
			break;
		
		case STORE_ATTR:
			name = GETNAME(oparg);
			v = POP();
			u = POP();
			err = setattr(v, name, u); /* v.name = u */
			DECREF(v);
			DECREF(u);
			break;
		
		case DELETE_ATTR:
			name = GETNAME(oparg);
			v = POP();
			err = setattr(v, name, (object *)NULL);
							/* del v.name */
			DECREF(v);
			break;
		
		case LOAD_CONST:
			x = GETCONST(oparg);
			INCREF(x);
			PUSH(x);
			break;
		
		case LOAD_NAME:
			name = GETNAME(oparg);
			x = dictlookup(f->f_locals, name);
			if (x == NULL) {
				x = dictlookup(f->f_globals, name);
				if (x == NULL)
					x = getbuiltin(name);
			}
			if (x == NULL)
				err_setstr(NameError, name);
			else
				INCREF(x);
			PUSH(x);
			break;
		
		case BUILD_TUPLE:
			x = newtupleobject(oparg);
			if (x != NULL) {
				for (; --oparg >= 0;) {
					w = POP();
					err = settupleitem(x, oparg, w);
					if (err != 0)
						break;
				}
				PUSH(x);
			}
			break;
		
		case BUILD_LIST:
			x =  newlistobject(oparg);
			if (x != NULL) {
				for (; --oparg >= 0;) {
					w = POP();
					err = setlistitem(x, oparg, w);
					if (err != 0)
						break;
				}
				PUSH(x);
			}
			break;
		
		case BUILD_MAP:
			x = newdictobject();
			PUSH(x);
			break;
		
		case LOAD_ATTR:
			name = GETNAME(oparg);
			v = POP();
			x = getattr(v, name);
			DECREF(v);
			PUSH(x);
			break;
		
		case COMPARE_OP:
			w = POP();
			v = POP();
			x = cmp_outcome((enum cmp_op)oparg, v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case IMPORT_NAME:
			name = GETNAME(oparg);
			x = import_module(name);
			XINCREF(x);
			PUSH(x);
			break;
		
		case IMPORT_FROM:
			name = GETNAME(oparg);
			v = TOP();
			err = import_from(f->f_locals, v, name);
			break;
		
		case JUMP_FORWARD:
			JUMPBY(oparg);
			break;
		
		case JUMP_IF_FALSE:
			if (!testbool(TOP()))
				JUMPBY(oparg);
			break;
		
		case JUMP_IF_TRUE:
			if (testbool(TOP()))
				JUMPBY(oparg);
			break;
		
		case JUMP_ABSOLUTE:
			JUMPTO(oparg);
			break;
		
		case FOR_LOOP:
			/* for v in s: ...
			   On entry: stack contains s, i.
			   On exit: stack contains s, i+1, s[i];
			   but if loop exhausted:
			   	s, i are popped, and we jump */
			w = POP(); /* Loop index */
			v = POP(); /* Sequence object */
			u = loop_subscript(v, w);
			if (u != NULL) {
				PUSH(v);
				x = newintobject(getintvalue(w)+1);
				PUSH(x);
				DECREF(w);
				PUSH(u);
			}
			else {
				DECREF(v);
				DECREF(w);
				/* A NULL can mean "s exhausted"
				   but also an error: */
				if (err_occurred())
					why = WHY_EXCEPTION;
				else
					JUMPBY(oparg);
			}
			break;
		
		case SETUP_LOOP:
		case SETUP_EXCEPT:
		case SETUP_FINALLY:
			setup_block(f, opcode, INSTR_OFFSET() + oparg,
						STACK_LEVEL());
			break;
		
		case SET_LINENO:
#ifdef TRACE
			if (trace)
				printf("--- Line %d ---\n", oparg);
#endif
			lineno = oparg;
			break;
		
		default:
			fprintf(stderr,
				"XXX lineno: %d, opcode: %d\n",
				lineno, opcode);
			err_setstr(SystemError, "eval_code: unknown opcode");
			why = WHY_EXCEPTION;
			break;
		
		} /* switch */

		
		/* Quickly continue if no error occurred */
		
		if (why == WHY_NOT) {
			if (err == 0 && x != NULL)
				continue; /* Normal, fast path */
			why = WHY_EXCEPTION;
			x = None;
			err = 0;
		}

#ifndef NDEBUG
		/* Double-check exception status */
		
		if (why == WHY_EXCEPTION || why == WHY_RERAISE) {
			if (!err_occurred()) {
				fprintf(stderr, "XXX ghost error\n");
				err_setstr(SystemError, "ghost error");
				why = WHY_EXCEPTION;
			}
		}
		else {
			if (err_occurred()) {
				fprintf(stderr, "XXX undetected error\n");
				why = WHY_EXCEPTION;
			}
		}
#endif

		/* Log traceback info if this is a real exception */
		
		if (why == WHY_EXCEPTION) {
			int lasti = INSTR_OFFSET() - 1;
			if (HAS_ARG(opcode))
				lasti -= 2;
			tb_here(f, lasti, lineno);
		}
		
		/* For the rest, treat WHY_RERAISE as WHY_EXCEPTION */
		
		if (why == WHY_RERAISE)
			why = WHY_EXCEPTION;

		/* Unwind stacks if a (pseudo) exception occurred */
		
		while (why != WHY_NOT && f->f_iblock > 0) {
			block *b = pop_block(f);
			while (STACK_LEVEL() > b->b_level) {
				v = POP();
				XDECREF(v);
			}
			if (b->b_type == SETUP_LOOP && why == WHY_BREAK) {
				why = WHY_NOT;
				JUMPTO(b->b_handler);
				break;
			}
			if (b->b_type == SETUP_FINALLY ||
					b->b_type == SETUP_EXCEPT &&
					why == WHY_EXCEPTION) {
				if (why == WHY_EXCEPTION) {
					object *exc, *val;
					err_get(&exc, &val);
					if (val == NULL) {
						val = None;
						INCREF(val);
					}
					v = tb_fetch();
					/* Make the raw exception data
					   available to the handler,
					   so a program can emulate the
					   Python main loop.  Don't do
					   this for 'finally'. */
					if (b->b_type == SETUP_EXCEPT) {
#if 0 /* Oops, this breaks too many things */
						sysset("exc_traceback", v);
#endif
						sysset("exc_value", val);
						sysset("exc_type", exc);
						err_clear();
					}
					PUSH(v);
					PUSH(val);
					PUSH(exc);
				}
				else {
					if (why == WHY_RETURN)
						PUSH(retval);
					v = newintobject((long)why);
					PUSH(v);
				}
				why = WHY_NOT;
				JUMPTO(b->b_handler);
				break;
			}
		} /* unwind stack */

		/* End the loop if we still have an error (or return) */
		
		if (why != WHY_NOT)
			break;
		
	} /* main loop */
	
	/* Pop remaining stack entries */
	
	while (!EMPTY()) {
		v = POP();
		XDECREF(v);
	}
	
	/* Restore previous frame and release the current one */
	
	current_frame = f->f_back;
	DECREF(f);
	
	if (why == WHY_RETURN)
		return retval;
	else
		return NULL;
}