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Issue #7298: Fix a variety of problems leading to wrong results with 

the fast versions of range.__reversed__ and range iteration.  Also
fix wrong results and a refleak for PyLong version of range.__reversed__.

Thanks Eric Smith for reviewing, and for suggesting improved tests.
This commit is contained in:
Mark Dickinson 2009-11-15 09:57:26 +00:00
parent 4c7eaee5db
commit d550c9a281
3 changed files with 207 additions and 57 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
Lib/test/test_range.py
View File

@ -3,12 +3,49 @@
import test.support, unittest
import sys
import pickle
import itertools
import warnings
warnings.filterwarnings("ignore", "integer argument expected",
DeprecationWarning, "unittest")
# pure Python implementations (3 args only), for comparison
def pyrange(start, stop, step):
if (start - stop) // step < 0:
# replace stop with next element in the sequence of integers
# that are congruent to start modulo step.
stop += (start - stop) % step
while start != stop:
yield start
start += step
def pyrange_reversed(start, stop, step):
stop += (start - stop) % step
return pyrange(stop - step, start - step, -step)
class RangeTest(unittest.TestCase):
def assert_iterators_equal(self, xs, ys, test_id, limit=None):
# check that an iterator xs matches the expected results ys,
# up to a given limit.
if limit is not None:
xs = itertools.islice(xs, limit)
ys = itertools.islice(ys, limit)
sentinel = object()
pairs = itertools.zip_longest(xs, ys, fillvalue=sentinel)
for i, (x, y) in enumerate(pairs):
if x == y:
continue
elif x == sentinel:
self.fail('{}: iterator ended unexpectedly '
'at position {}; expected {}'.format(test_id, i, y))
elif y == sentinel:
self.fail('{}: unexpected excess element {} at '
'position {}'.format(test_id, x, i))
else:
self.fail('{}: wrong element at position {};'
'expected {}, got {}'.format(test_id, i, y, x))
def test_range(self):
self.assertEqual(list(range(3)), [0, 1, 2])
self.assertEqual(list(range(1, 5)), [1, 2, 3, 4])
@ -134,6 +171,30 @@ class RangeTest(unittest.TestCase):
self.assertFalse(-1 in r)
self.assertFalse(1 in r)
def test_range_iterators(self):
# exercise 'fast' iterators, that use a rangeiterobject internally.
# see issue 7298
limits = [base + jiggle
for M in (2**32, 2**64)
for base in (-M, -M//2, 0, M//2, M)
for jiggle in (-2, -1, 0, 1, 2)]
test_ranges = [(start, end, step)
for start in limits
for end in limits
for step in (-2**63, -2**31, -2, -1, 1, 2)]
for start, end, step in test_ranges:
iter1 = range(start, end, step)
iter2 = pyrange(start, end, step)
test_id = "range({}, {}, {})".format(start, end, step)
# check first 100 entries
self.assert_iterators_equal(iter1, iter2, test_id, limit=100)
iter1 = reversed(range(start, end, step))
iter2 = pyrange_reversed(start, end, step)
test_id = "reversed(range({}, {}, {}))".format(start, end, step)
self.assert_iterators_equal(iter1, iter2, test_id, limit=100)
def test_main():
test.support.run_unittest(RangeTest)

6
Misc/NEWS
View File

@ -12,6 +12,12 @@ What's New in Python 3.2 Alpha 1?
Core and Builtins
-----------------
- Issue #7298: fixes for range and reversed(range(...)). Iteration
over range(a, b, c) incorrectly gave an empty iterator when a, b and
c fit in C long but the length of the range did not. Also fix
several cases where reversed(range(a, b, c)) gave wrong results, and
fix a refleak for reversed(range(a, b, c)) with large arguments.
- Issue #7244: itertools.izip_longest() no longer ignores exceptions
raised during the formation of an output tuple.

197
Objects/rangeobject.c
View File

@ -488,16 +488,15 @@ PyTypeObject PyRangeIter_Type = {
rangeiter_new, /* tp_new */
};
/* Return number of items in range (lo, hi, step). step > 0
* required. Return a value < 0 if & only if the true value is too
* large to fit in a signed long.
/* Return number of items in range (lo, hi, step). step != 0
* required. The result always fits in an unsigned long.
*/
static long
static unsigned long
get_len_of_range(long lo, long hi, long step)
{
/* -------------------------------------------------------------
If lo >= hi, the range is empty.
Else if n values are in the range, the last one is
If step > 0 and lo >= hi, or step < 0 and lo <= hi, the range is empty.
Else for step > 0, if n values are in the range, the last one is
lo + (n-1)*step, which must be <= hi-1. Rearranging,
n <= (hi - lo - 1)/step + 1, so taking the floor of the RHS gives
the proper value. Since lo < hi in this case, hi-lo-1 >= 0, so
@ -505,30 +504,37 @@ get_len_of_range(long lo, long hi, long step)
floor. Letting M be the largest positive long, the worst case
for the RHS numerator is hi=M, lo=-M-1, and then
hi-lo-1 = M-(-M-1)-1 = 2*M. Therefore unsigned long has enough
precision to compute the RHS exactly.
precision to compute the RHS exactly. The analysis for step < 0
is similar.
---------------------------------------------------------------*/
long n = 0;
if (lo < hi) {
unsigned long uhi = (unsigned long)hi;
unsigned long ulo = (unsigned long)lo;
unsigned long diff = uhi - ulo - 1;
n = (long)(diff / (unsigned long)step + 1);
}
return n;
assert(step != 0);
if (step > 0 && lo < hi)
return 1UL + (hi - 1UL - lo) / step;
else if (step < 0 && lo > hi)
return 1UL + (lo - 1UL - hi) / (0UL - step);
else
return 0UL;
}
/* Initialize a rangeiter object. If the length of the rangeiter object
is not representable as a C long, OverflowError is raised. */
static PyObject *
int_range_iter(long start, long stop, long step)
{
rangeiterobject *it = PyObject_New(rangeiterobject, &PyRangeIter_Type);
unsigned long ulen;
if (it == NULL)
return NULL;
it->start = start;
it->step = step;
if (step > 0)
it->len = get_len_of_range(start, stop, step);
else
it->len = get_len_of_range(stop, start, -step);
ulen = get_len_of_range(start, stop, step);
if (ulen > (unsigned long)LONG_MAX) {
PyErr_SetString(PyExc_OverflowError,
"range too large to represent as a range_iterator");
return NULL;
}
it->len = (long)ulen;
it->index = 0;
return (PyObject *)it;
}
@ -637,23 +643,53 @@ range_iter(PyObject *seq)
rangeobject *r = (rangeobject *)seq;
longrangeiterobject *it;
long lstart, lstop, lstep;
PyObject *int_it;
assert(PyRange_Check(seq));
/* If all three fields convert to long, use the int version */
/* If all three fields and the length convert to long, use the int
* version */
lstart = PyLong_AsLong(r->start);
if (lstart != -1 || !PyErr_Occurred()) {
lstop = PyLong_AsLong(r->stop);
if (lstop != -1 || !PyErr_Occurred()) {
lstep = PyLong_AsLong(r->step);
if (lstep != -1 || !PyErr_Occurred())
return int_range_iter(lstart, lstop, lstep);
}
if (lstart == -1 && PyErr_Occurred()) {
PyErr_Clear();
goto long_range;
}
/* Some conversion failed, so there is an error set. Clear it,
and try again with a long range. */
PyErr_Clear();
lstop = PyLong_AsLong(r->stop);
if (lstop == -1 && PyErr_Occurred()) {
PyErr_Clear();
goto long_range;
}
lstep = PyLong_AsLong(r->step);
if (lstep == -1 && PyErr_Occurred()) {
PyErr_Clear();
goto long_range;
}
/* round lstop to the next value congruent to lstart modulo lstep;
if the result would overflow, use PyLong version. */
if (lstep > 0 && lstart < lstop) {
long extra = (lstep - 1) - (long)((lstop - 1UL - lstart) % lstep);
if ((unsigned long)extra > (unsigned long)LONG_MAX - lstop)
goto long_range;
lstop += extra;
}
else if (lstep < 0 && lstart > lstop) {
long extra = (lstep + 1) + (long)((lstart - 1UL - lstop) %
(0UL - lstep));
if ((unsigned long)lstop - LONG_MIN < 0UL - extra)
goto long_range;
lstop += extra;
}
else
lstop = lstart;
int_it = int_range_iter(lstart, lstop, lstep);
if (int_it == NULL && PyErr_ExceptionMatches(PyExc_OverflowError)) {
PyErr_Clear();
goto long_range;
}
return (PyObject *)int_it;
long_range:
it = PyObject_New(longrangeiterobject, &PyLongRangeIter_Type);
if (it == NULL)
return NULL;
@ -686,34 +722,80 @@ range_reverse(PyObject *seq)
rangeobject *range = (rangeobject*) seq;
longrangeiterobject *it;
PyObject *one, *sum, *diff, *len = NULL, *product;
long lstart, lstop, lstep;
long lstart, lstop, lstep, new_start, new_stop;
unsigned long ulen;
/* XXX(nnorwitz): do the calc for the new start/stop first,
then if they fit, call the proper iter()?
*/
assert(PyRange_Check(seq));
/* If all three fields convert to long, use the int version */
lstart = PyLong_AsLong(range->start);
if (lstart != -1 || !PyErr_Occurred()) {
lstop = PyLong_AsLong(range->stop);
if (lstop != -1 || !PyErr_Occurred()) {
lstep = PyLong_AsLong(range->step);
if (lstep != -1 || !PyErr_Occurred()) {
/* XXX(nnorwitz): need to check for overflow and simplify. */
long len = get_len_of_range(lstart, lstop, lstep);
long new_start = lstart + (len - 1) * lstep;
long new_stop = lstart;
if (lstep > 0)
new_stop -= 1;
else
new_stop += 1;
return int_range_iter(new_start, new_stop, -lstep);
}
}
}
PyErr_Clear();
/* reversed(range(start, stop, step)) can be expressed as
range(start+(n-1)*step, start-step, -step), where n is the number of
integers in the range.
If each of start, stop, step, -step, start-step, and the length
of the iterator is representable as a C long, use the int
version. This excludes some cases where the reversed range is
representable as a range_iterator, but it's good enough for
common cases and it makes the checks simple. */
lstart = PyLong_AsLong(range->start);
if (lstart == -1 && PyErr_Occurred()) {
PyErr_Clear();
goto long_range;
}
lstop = PyLong_AsLong(range->stop);
if (lstop == -1 && PyErr_Occurred()) {
PyErr_Clear();
goto long_range;
}
lstep = PyLong_AsLong(range->step);
if (lstep == -1 && PyErr_Occurred()) {
PyErr_Clear();
goto long_range;
}
/* check for possible overflow of -lstep */
if (lstep == LONG_MIN)
goto long_range;
/* check for overflow of lstart - lstep:
for lstep > 0, need only check whether lstart - lstep < LONG_MIN.
for lstep < 0, need only check whether lstart - lstep > LONG_MAX
Rearrange these inequalities as:
lstart - LONG_MIN < lstep (lstep > 0)
LONG_MAX - lstart < -lstep (lstep < 0)
and compute both sides as unsigned longs, to avoid the
possibility of undefined behaviour due to signed overflow. */
if (lstep > 0) {
if ((unsigned long)lstart - LONG_MIN < (unsigned long)lstep)
goto long_range;
}
else {
if (LONG_MAX - (unsigned long)lstart < 0UL - lstep)
goto long_range;
}
/* set lstop equal to the last element of the range, or to lstart if the
range is empty. */
if (lstep > 0 && lstart < lstop)
lstop += -1 - (long)((lstop - 1UL - lstart) % lstep);
else if (lstep < 0 && lstart > lstop)
lstop += 1 + (long)((lstart - 1UL - lstop) % (0UL - lstep));
else
lstop = lstart;
ulen = get_len_of_range(lstart, lstop, lstep);
if (ulen > (unsigned long)LONG_MAX)
goto long_range;
new_stop = lstart - lstep;
new_start = (long)(new_stop + ulen * lstep);
return int_range_iter(new_start, new_stop, -lstep);
long_range:
it = PyObject_New(longrangeiterobject, &PyLongRangeIter_Type);
if (it == NULL)
return NULL;
@ -732,7 +814,8 @@ range_reverse(PyObject *seq)
if (!diff)
goto create_failure;
product = PyNumber_Multiply(len, range->step);
product = PyNumber_Multiply(diff, range->step);
Py_DECREF(diff);
if (!product)
goto create_failure;
@ -741,11 +824,11 @@ range_reverse(PyObject *seq)
it->start = sum;
if (!it->start)
goto create_failure;
it->step = PyNumber_Negative(range->step);
if (!it->step) {
Py_DECREF(it->start);
PyObject_Del(it);
return NULL;
goto create_failure;
}
/* Steal reference to len. */