From 918403cfc3304d27e80fb792357f40bb3ba69c4e Mon Sep 17 00:00:00 2001 From: Serhiy Storchaka Date: Thu, 30 Mar 2017 09:47:07 +0300 Subject: bpo-29816: Shift operation now has less opportunity to raise OverflowError. (#680) ValueError always is raised rather than OverflowError for negative counts. Shifting zero with non-negative count always returns zero. --- Lib/test/test_long.py | 32 +++++++++++++++++++++-- Misc/NEWS | 4 +++ Objects/longobject.c | 70 +++++++++++++++++++++++++++++++++++---------------- 3 files changed, 82 insertions(+), 24 deletions(-) diff --git a/Lib/test/test_long.py b/Lib/test/test_long.py index fd15f04..cc48259 100644 --- a/Lib/test/test_long.py +++ b/Lib/test/test_long.py @@ -906,11 +906,24 @@ class LongTest(unittest.TestCase): self.check_truediv(-x, y) self.check_truediv(-x, -y) + def test_negative_shift_count(self): + with self.assertRaises(ValueError): + 42 << -3 + with self.assertRaises(ValueError): + 42 << -(1 << 1000) + with self.assertRaises(ValueError): + 42 >> -3 + with self.assertRaises(ValueError): + 42 >> -(1 << 1000) + def test_lshift_of_zero(self): self.assertEqual(0 << 0, 0) self.assertEqual(0 << 10, 0) with self.assertRaises(ValueError): 0 << -1 + self.assertEqual(0 << (1 << 1000), 0) + with self.assertRaises(ValueError): + 0 << -(1 << 1000) @support.cpython_only def test_huge_lshift_of_zero(self): @@ -918,8 +931,23 @@ class LongTest(unittest.TestCase): # Other implementations may have a different boundary for overflow, # or not raise at all. self.assertEqual(0 << sys.maxsize, 0) - with self.assertRaises(OverflowError): - 0 << (sys.maxsize + 1) + self.assertEqual(0 << (sys.maxsize + 1), 0) + + @support.cpython_only + @support.bigmemtest(sys.maxsize + 1000, memuse=2/15 * 2, dry_run=False) + def test_huge_lshift(self, size): + self.assertEqual(1 << (sys.maxsize + 1000), 1 << 1000 << sys.maxsize) + + def test_huge_rshift(self): + self.assertEqual(42 >> (1 << 1000), 0) + self.assertEqual((-42) >> (1 << 1000), -1) + + @support.cpython_only + @support.bigmemtest(sys.maxsize + 500, memuse=2/15, dry_run=False) + def test_huge_rshift_of_huge(self, size): + huge = ((1 << 500) + 11) << sys.maxsize + self.assertEqual(huge >> (sys.maxsize + 1), (1 << 499) + 5) + self.assertEqual(huge >> (sys.maxsize + 1000), 0) def test_small_ints(self): for i in range(-5, 257): diff --git a/Misc/NEWS b/Misc/NEWS index b22322f..2bea5ec 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -10,6 +10,10 @@ What's New in Python 3.7.0 alpha 1? Core and Builtins ----------------- +- bpo-29816: Shift operation now has less opportunity to raise OverflowError. + ValueError always is raised rather than OverflowError for negative counts. + Shifting zero with non-negative count always returns zero. + - bpo-24821: Fixed the slowing down to 25 times in the searching of some unlucky Unicode characters. diff --git a/Objects/longobject.c b/Objects/longobject.c index 459eed9..4862b76 100644 --- a/Objects/longobject.c +++ b/Objects/longobject.c @@ -4277,15 +4277,54 @@ long_bool(PyLongObject *v) return Py_SIZE(v) != 0; } +/* wordshift, remshift = divmod(shiftby, PyLong_SHIFT) */ +static int +divmod_shift(PyLongObject *shiftby, Py_ssize_t *wordshift, digit *remshift) +{ + assert(PyLong_Check((PyObject *)shiftby)); + assert(Py_SIZE(shiftby) >= 0); + Py_ssize_t lshiftby = PyLong_AsSsize_t((PyObject *)shiftby); + if (lshiftby >= 0) { + *wordshift = lshiftby / PyLong_SHIFT; + *remshift = lshiftby % PyLong_SHIFT; + return 0; + } + /* PyLong_Check(shiftby) is true and Py_SIZE(shiftby) >= 0, so it must + be that PyLong_AsSsize_t raised an OverflowError. */ + assert(PyErr_ExceptionMatches(PyExc_OverflowError)); + PyErr_Clear(); + PyLongObject *wordshift_obj = divrem1(shiftby, PyLong_SHIFT, remshift); + if (wordshift_obj == NULL) { + return -1; + } + *wordshift = PyLong_AsSsize_t((PyObject *)wordshift_obj); + Py_DECREF(wordshift_obj); + if (*wordshift >= 0 && *wordshift < PY_SSIZE_T_MAX / (Py_ssize_t)sizeof(digit)) { + return 0; + } + PyErr_Clear(); + /* Clip the value. With such large wordshift the right shift + returns 0 and the left shift raises an error in _PyLong_New(). */ + *wordshift = PY_SSIZE_T_MAX / sizeof(digit); + *remshift = 0; + return 0; +} + static PyObject * long_rshift(PyLongObject *a, PyLongObject *b) { PyLongObject *z = NULL; - Py_ssize_t shiftby, newsize, wordshift, loshift, hishift, i, j; - digit lomask, himask; + Py_ssize_t newsize, wordshift, hishift, i, j; + digit loshift, lomask, himask; CHECK_BINOP(a, b); + if (Py_SIZE(b) < 0) { + PyErr_SetString(PyExc_ValueError, + "negative shift count"); + return NULL; + } + if (Py_SIZE(a) < 0) { /* Right shifting negative numbers is harder */ PyLongObject *a1, *a2; @@ -4300,19 +4339,11 @@ long_rshift(PyLongObject *a, PyLongObject *b) Py_DECREF(a2); } else { - shiftby = PyLong_AsSsize_t((PyObject *)b); - if (shiftby == -1L && PyErr_Occurred()) - return NULL; - if (shiftby < 0) { - PyErr_SetString(PyExc_ValueError, - "negative shift count"); + if (divmod_shift(b, &wordshift, &loshift) < 0) return NULL; - } - wordshift = shiftby / PyLong_SHIFT; - newsize = Py_ABS(Py_SIZE(a)) - wordshift; + newsize = Py_SIZE(a) - wordshift; if (newsize <= 0) return PyLong_FromLong(0); - loshift = shiftby % PyLong_SHIFT; hishift = PyLong_SHIFT - loshift; lomask = ((digit)1 << hishift) - 1; himask = PyLong_MASK ^ lomask; @@ -4336,27 +4367,22 @@ long_lshift(PyObject *v, PyObject *w) PyLongObject *a = (PyLongObject*)v; PyLongObject *b = (PyLongObject*)w; PyLongObject *z = NULL; - Py_ssize_t shiftby, oldsize, newsize, wordshift, remshift, i, j; + Py_ssize_t oldsize, newsize, wordshift, i, j; + digit remshift; twodigits accum; CHECK_BINOP(a, b); - shiftby = PyLong_AsSsize_t((PyObject *)b); - if (shiftby == -1L && PyErr_Occurred()) - return NULL; - if (shiftby < 0) { + if (Py_SIZE(b) < 0) { PyErr_SetString(PyExc_ValueError, "negative shift count"); return NULL; } - if (Py_SIZE(a) == 0) { return PyLong_FromLong(0); } - /* wordshift, remshift = divmod(shiftby, PyLong_SHIFT) */ - wordshift = shiftby / PyLong_SHIFT; - remshift = shiftby - wordshift * PyLong_SHIFT; - + if (divmod_shift(b, &wordshift, &remshift) < 0) + return NULL; oldsize = Py_ABS(Py_SIZE(a)); newsize = oldsize + wordshift; if (remshift) -- cgit v0.12