mirror of https://github.com/python/cpython
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
parent
4c7eaee5db
commit
d550c9a281
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@ -3,12 +3,49 @@
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import test.support, unittest
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import sys
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import pickle
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import itertools
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import warnings
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warnings.filterwarnings("ignore", "integer argument expected",
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DeprecationWarning, "unittest")
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# pure Python implementations (3 args only), for comparison
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def pyrange(start, stop, step):
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if (start - stop) // step < 0:
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# replace stop with next element in the sequence of integers
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# that are congruent to start modulo step.
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stop += (start - stop) % step
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while start != stop:
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yield start
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start += step
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def pyrange_reversed(start, stop, step):
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stop += (start - stop) % step
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return pyrange(stop - step, start - step, -step)
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class RangeTest(unittest.TestCase):
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def assert_iterators_equal(self, xs, ys, test_id, limit=None):
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# check that an iterator xs matches the expected results ys,
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# up to a given limit.
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if limit is not None:
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xs = itertools.islice(xs, limit)
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ys = itertools.islice(ys, limit)
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sentinel = object()
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pairs = itertools.zip_longest(xs, ys, fillvalue=sentinel)
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for i, (x, y) in enumerate(pairs):
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if x == y:
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continue
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elif x == sentinel:
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self.fail('{}: iterator ended unexpectedly '
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'at position {}; expected {}'.format(test_id, i, y))
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elif y == sentinel:
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self.fail('{}: unexpected excess element {} at '
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'position {}'.format(test_id, x, i))
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else:
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self.fail('{}: wrong element at position {};'
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'expected {}, got {}'.format(test_id, i, y, x))
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def test_range(self):
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self.assertEqual(list(range(3)), [0, 1, 2])
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self.assertEqual(list(range(1, 5)), [1, 2, 3, 4])
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@ -134,6 +171,30 @@ class RangeTest(unittest.TestCase):
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self.assertFalse(-1 in r)
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self.assertFalse(1 in r)
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def test_range_iterators(self):
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# exercise 'fast' iterators, that use a rangeiterobject internally.
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# see issue 7298
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limits = [base + jiggle
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for M in (2**32, 2**64)
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for base in (-M, -M//2, 0, M//2, M)
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for jiggle in (-2, -1, 0, 1, 2)]
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test_ranges = [(start, end, step)
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for start in limits
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for end in limits
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for step in (-2**63, -2**31, -2, -1, 1, 2)]
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for start, end, step in test_ranges:
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iter1 = range(start, end, step)
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iter2 = pyrange(start, end, step)
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test_id = "range({}, {}, {})".format(start, end, step)
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# check first 100 entries
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self.assert_iterators_equal(iter1, iter2, test_id, limit=100)
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iter1 = reversed(range(start, end, step))
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iter2 = pyrange_reversed(start, end, step)
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test_id = "reversed(range({}, {}, {}))".format(start, end, step)
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self.assert_iterators_equal(iter1, iter2, test_id, limit=100)
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def test_main():
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test.support.run_unittest(RangeTest)
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@ -12,6 +12,12 @@ What's New in Python 3.2 Alpha 1?
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Core and Builtins
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-----------------
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- Issue #7298: fixes for range and reversed(range(...)). Iteration
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over range(a, b, c) incorrectly gave an empty iterator when a, b and
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c fit in C long but the length of the range did not. Also fix
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several cases where reversed(range(a, b, c)) gave wrong results, and
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fix a refleak for reversed(range(a, b, c)) with large arguments.
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- Issue #7244: itertools.izip_longest() no longer ignores exceptions
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raised during the formation of an output tuple.
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@ -488,16 +488,15 @@ PyTypeObject PyRangeIter_Type = {
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rangeiter_new, /* tp_new */
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};
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/* Return number of items in range (lo, hi, step). step > 0
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* required. Return a value < 0 if & only if the true value is too
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* large to fit in a signed long.
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/* Return number of items in range (lo, hi, step). step != 0
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* required. The result always fits in an unsigned long.
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*/
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static long
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static unsigned long
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get_len_of_range(long lo, long hi, long step)
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{
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/* -------------------------------------------------------------
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If lo >= hi, the range is empty.
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Else if n values are in the range, the last one is
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If step > 0 and lo >= hi, or step < 0 and lo <= hi, the range is empty.
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Else for step > 0, if n values are in the range, the last one is
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lo + (n-1)*step, which must be <= hi-1. Rearranging,
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n <= (hi - lo - 1)/step + 1, so taking the floor of the RHS gives
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the proper value. Since lo < hi in this case, hi-lo-1 >= 0, so
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@ -505,30 +504,37 @@ get_len_of_range(long lo, long hi, long step)
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floor. Letting M be the largest positive long, the worst case
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for the RHS numerator is hi=M, lo=-M-1, and then
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hi-lo-1 = M-(-M-1)-1 = 2*M. Therefore unsigned long has enough
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precision to compute the RHS exactly.
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precision to compute the RHS exactly. The analysis for step < 0
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is similar.
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---------------------------------------------------------------*/
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long n = 0;
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if (lo < hi) {
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unsigned long uhi = (unsigned long)hi;
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unsigned long ulo = (unsigned long)lo;
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unsigned long diff = uhi - ulo - 1;
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n = (long)(diff / (unsigned long)step + 1);
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}
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return n;
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assert(step != 0);
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if (step > 0 && lo < hi)
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return 1UL + (hi - 1UL - lo) / step;
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else if (step < 0 && lo > hi)
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return 1UL + (lo - 1UL - hi) / (0UL - step);
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else
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return 0UL;
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}
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/* Initialize a rangeiter object. If the length of the rangeiter object
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is not representable as a C long, OverflowError is raised. */
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static PyObject *
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int_range_iter(long start, long stop, long step)
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{
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rangeiterobject *it = PyObject_New(rangeiterobject, &PyRangeIter_Type);
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unsigned long ulen;
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if (it == NULL)
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return NULL;
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it->start = start;
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it->step = step;
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if (step > 0)
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it->len = get_len_of_range(start, stop, step);
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else
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it->len = get_len_of_range(stop, start, -step);
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ulen = get_len_of_range(start, stop, step);
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if (ulen > (unsigned long)LONG_MAX) {
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PyErr_SetString(PyExc_OverflowError,
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"range too large to represent as a range_iterator");
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return NULL;
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}
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it->len = (long)ulen;
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it->index = 0;
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return (PyObject *)it;
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}
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@ -637,23 +643,53 @@ range_iter(PyObject *seq)
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rangeobject *r = (rangeobject *)seq;
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longrangeiterobject *it;
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long lstart, lstop, lstep;
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PyObject *int_it;
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assert(PyRange_Check(seq));
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/* If all three fields convert to long, use the int version */
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/* If all three fields and the length convert to long, use the int
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* version */
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lstart = PyLong_AsLong(r->start);
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if (lstart != -1 || !PyErr_Occurred()) {
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lstop = PyLong_AsLong(r->stop);
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if (lstop != -1 || !PyErr_Occurred()) {
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lstep = PyLong_AsLong(r->step);
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if (lstep != -1 || !PyErr_Occurred())
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return int_range_iter(lstart, lstop, lstep);
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}
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}
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/* Some conversion failed, so there is an error set. Clear it,
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and try again with a long range. */
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if (lstart == -1 && PyErr_Occurred()) {
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PyErr_Clear();
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goto long_range;
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}
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lstop = PyLong_AsLong(r->stop);
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if (lstop == -1 && PyErr_Occurred()) {
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PyErr_Clear();
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goto long_range;
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}
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lstep = PyLong_AsLong(r->step);
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if (lstep == -1 && PyErr_Occurred()) {
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PyErr_Clear();
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goto long_range;
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}
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/* round lstop to the next value congruent to lstart modulo lstep;
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if the result would overflow, use PyLong version. */
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if (lstep > 0 && lstart < lstop) {
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long extra = (lstep - 1) - (long)((lstop - 1UL - lstart) % lstep);
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if ((unsigned long)extra > (unsigned long)LONG_MAX - lstop)
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goto long_range;
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lstop += extra;
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}
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else if (lstep < 0 && lstart > lstop) {
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long extra = (lstep + 1) + (long)((lstart - 1UL - lstop) %
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(0UL - lstep));
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if ((unsigned long)lstop - LONG_MIN < 0UL - extra)
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goto long_range;
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lstop += extra;
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}
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else
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lstop = lstart;
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int_it = int_range_iter(lstart, lstop, lstep);
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if (int_it == NULL && PyErr_ExceptionMatches(PyExc_OverflowError)) {
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PyErr_Clear();
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goto long_range;
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}
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return (PyObject *)int_it;
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long_range:
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it = PyObject_New(longrangeiterobject, &PyLongRangeIter_Type);
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if (it == NULL)
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return NULL;
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@ -686,34 +722,80 @@ range_reverse(PyObject *seq)
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rangeobject *range = (rangeobject*) seq;
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longrangeiterobject *it;
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PyObject *one, *sum, *diff, *len = NULL, *product;
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long lstart, lstop, lstep;
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long lstart, lstop, lstep, new_start, new_stop;
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unsigned long ulen;
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/* XXX(nnorwitz): do the calc for the new start/stop first,
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then if they fit, call the proper iter()?
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*/
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assert(PyRange_Check(seq));
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/* If all three fields convert to long, use the int version */
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lstart = PyLong_AsLong(range->start);
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if (lstart != -1 || !PyErr_Occurred()) {
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lstop = PyLong_AsLong(range->stop);
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if (lstop != -1 || !PyErr_Occurred()) {
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lstep = PyLong_AsLong(range->step);
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if (lstep != -1 || !PyErr_Occurred()) {
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/* XXX(nnorwitz): need to check for overflow and simplify. */
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long len = get_len_of_range(lstart, lstop, lstep);
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long new_start = lstart + (len - 1) * lstep;
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long new_stop = lstart;
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if (lstep > 0)
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new_stop -= 1;
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else
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new_stop += 1;
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return int_range_iter(new_start, new_stop, -lstep);
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}
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}
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}
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PyErr_Clear();
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/* reversed(range(start, stop, step)) can be expressed as
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range(start+(n-1)*step, start-step, -step), where n is the number of
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integers in the range.
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If each of start, stop, step, -step, start-step, and the length
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of the iterator is representable as a C long, use the int
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version. This excludes some cases where the reversed range is
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representable as a range_iterator, but it's good enough for
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common cases and it makes the checks simple. */
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lstart = PyLong_AsLong(range->start);
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if (lstart == -1 && PyErr_Occurred()) {
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PyErr_Clear();
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goto long_range;
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}
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lstop = PyLong_AsLong(range->stop);
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if (lstop == -1 && PyErr_Occurred()) {
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PyErr_Clear();
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goto long_range;
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}
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lstep = PyLong_AsLong(range->step);
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if (lstep == -1 && PyErr_Occurred()) {
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PyErr_Clear();
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goto long_range;
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}
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/* check for possible overflow of -lstep */
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if (lstep == LONG_MIN)
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goto long_range;
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/* check for overflow of lstart - lstep:
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for lstep > 0, need only check whether lstart - lstep < LONG_MIN.
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for lstep < 0, need only check whether lstart - lstep > LONG_MAX
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Rearrange these inequalities as:
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lstart - LONG_MIN < lstep (lstep > 0)
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LONG_MAX - lstart < -lstep (lstep < 0)
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and compute both sides as unsigned longs, to avoid the
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possibility of undefined behaviour due to signed overflow. */
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if (lstep > 0) {
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if ((unsigned long)lstart - LONG_MIN < (unsigned long)lstep)
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goto long_range;
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}
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else {
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if (LONG_MAX - (unsigned long)lstart < 0UL - lstep)
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goto long_range;
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}
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/* set lstop equal to the last element of the range, or to lstart if the
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range is empty. */
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if (lstep > 0 && lstart < lstop)
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lstop += -1 - (long)((lstop - 1UL - lstart) % lstep);
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else if (lstep < 0 && lstart > lstop)
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lstop += 1 + (long)((lstart - 1UL - lstop) % (0UL - lstep));
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else
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lstop = lstart;
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ulen = get_len_of_range(lstart, lstop, lstep);
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if (ulen > (unsigned long)LONG_MAX)
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goto long_range;
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new_stop = lstart - lstep;
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new_start = (long)(new_stop + ulen * lstep);
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return int_range_iter(new_start, new_stop, -lstep);
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long_range:
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it = PyObject_New(longrangeiterobject, &PyLongRangeIter_Type);
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if (it == NULL)
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return NULL;
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@ -732,7 +814,8 @@ range_reverse(PyObject *seq)
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if (!diff)
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goto create_failure;
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product = PyNumber_Multiply(len, range->step);
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product = PyNumber_Multiply(diff, range->step);
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Py_DECREF(diff);
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if (!product)
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goto create_failure;
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@ -741,11 +824,11 @@ range_reverse(PyObject *seq)
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it->start = sum;
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if (!it->start)
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goto create_failure;
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it->step = PyNumber_Negative(range->step);
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if (!it->step) {
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Py_DECREF(it->start);
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PyObject_Del(it);
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return NULL;
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goto create_failure;
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}
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/* Steal reference to len. */
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