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Issue #4707: round(x, n) now returns an integer when x is an integer.
Previously it returned a float.
This commit is contained in:
Mark Dickinson
parent
9de29afa7c
commit
1124e71368
@ -1068,9 +1068,9 @@ class BuiltinTest(unittest.TestCase):
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self.assertEqual(round(8), 8)
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self.assertEqual(round(-8), -8)
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self.assertEqual(type(round(0)), int)
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self.assertEqual(type(round(-8, -1)), float)
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self.assertEqual(type(round(-8, 0)), float)
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self.assertEqual(type(round(-8, 1)), float)
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self.assertEqual(type(round(-8, -1)), int)
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self.assertEqual(type(round(-8, 0)), int)
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self.assertEqual(type(round(-8, 1)), int)
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# test new kwargs
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self.assertEqual(round(number=-8.0, ndigits=-1), -10.0)
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@ -896,6 +896,81 @@ class LongTest(unittest.TestCase):
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self.assertEqual((a+1).bit_length(), i+1)
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self.assertEqual((-a-1).bit_length(), i+1)
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def test_round(self):
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# check round-half-even algorithm. For round to nearest ten;
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# rounding map is invariant under adding multiples of 20
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test_dict = {0:0, 1:0, 2:0, 3:0, 4:0, 5:0,
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6:10, 7:10, 8:10, 9:10, 10:10, 11:10, 12:10, 13:10, 14:10,
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15:20, 16:20, 17:20, 18:20, 19:20}
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for offset in range(-520, 520, 20):
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for k, v in test_dict.items():
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got = round(k+offset, -1)
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expected = v+offset
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self.assertEqual(got, expected)
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self.assert_(type(got) is int)
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# larger second argument
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self.assertEqual(round(-150, -2), -200)
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self.assertEqual(round(-149, -2), -100)
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self.assertEqual(round(-51, -2), -100)
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self.assertEqual(round(-50, -2), 0)
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self.assertEqual(round(-49, -2), 0)
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self.assertEqual(round(-1, -2), 0)
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self.assertEqual(round(0, -2), 0)
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self.assertEqual(round(1, -2), 0)
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self.assertEqual(round(49, -2), 0)
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self.assertEqual(round(50, -2), 0)
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self.assertEqual(round(51, -2), 100)
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self.assertEqual(round(149, -2), 100)
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self.assertEqual(round(150, -2), 200)
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self.assertEqual(round(250, -2), 200)
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self.assertEqual(round(251, -2), 300)
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self.assertEqual(round(172500, -3), 172000)
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self.assertEqual(round(173500, -3), 174000)
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self.assertEqual(round(31415926535, -1), 31415926540)
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self.assertEqual(round(31415926535, -2), 31415926500)
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self.assertEqual(round(31415926535, -3), 31415927000)
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self.assertEqual(round(31415926535, -4), 31415930000)
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self.assertEqual(round(31415926535, -5), 31415900000)
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self.assertEqual(round(31415926535, -6), 31416000000)
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self.assertEqual(round(31415926535, -7), 31420000000)
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self.assertEqual(round(31415926535, -8), 31400000000)
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self.assertEqual(round(31415926535, -9), 31000000000)
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self.assertEqual(round(31415926535, -10), 30000000000)
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self.assertEqual(round(31415926535, -11), 0)
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self.assertEqual(round(31415926535, -12), 0)
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self.assertEqual(round(31415926535, -999), 0)
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# should get correct results even for huge inputs
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for k in range(10, 100):
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got = round(10**k + 324678, -3)
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expect = 10**k + 325000
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self.assertEqual(got, expect)
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self.assert_(type(got) is int)
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# nonnegative second argument: round(x, n) should just return x
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for n in range(5):
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for i in range(100):
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x = random.randrange(-10000, 10000)
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got = round(x, n)
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self.assertEqual(got, x)
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self.assert_(type(got) is int)
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for huge_n in 2**31-1, 2**31, 2**63-1, 2**63, 2**100, 10**100:
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self.assertEqual(round(8979323, huge_n), 8979323)
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# omitted second argument
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for i in range(100):
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x = random.randrange(-10000, 10000)
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got = round(x)
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self.assertEqual(got, x)
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self.assert_(type(got) is int)
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# bad second argument
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bad_exponents = ('brian', 2.0, 0j, None)
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for e in bad_exponents:
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self.assertRaises(TypeError, round, 3, e)
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def test_main():
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support.run_unittest(LongTest)
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@ -12,6 +12,9 @@ What's New in Python 3.1 alpha 0
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Core and Builtins
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-----------------
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- Issue #4707: round(x, n) now returns an integer if x is an integer.
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Previously it returned a float.
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- Issue #4753: By enabling a configure option named '--with-computed-gotos'
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on compilers that support it (notably: gcc, SunPro, icc), the bytecode
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evaluation loop is compiled with a new dispatch mechanism which gives
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@ -3643,32 +3643,140 @@ long__format__(PyObject *self, PyObject *args)
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PyUnicode_GET_SIZE(format_spec));
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}
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static PyObject *
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long_round(PyObject *self, PyObject *args)
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{
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#define UNDEF_NDIGITS (-0x7fffffff) /* Unlikely ndigits value */
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int ndigits = UNDEF_NDIGITS;
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double x;
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PyObject *res;
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if (!PyArg_ParseTuple(args, "|i", &ndigits))
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return NULL;
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PyObject *o_ndigits=NULL, *temp;
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PyLongObject *pow=NULL, *q=NULL, *r=NULL, *ndigits=NULL, *one;
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int errcode;
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digit q_mod_4;
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if (ndigits == UNDEF_NDIGITS)
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/* Notes on the algorithm: to round to the nearest 10**n (n positive),
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the straightforward method is:
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(1) divide by 10**n
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(2) round to nearest integer (round to even in case of tie)
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(3) multiply result by 10**n.
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But the rounding step involves examining the fractional part of the
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quotient to see whether it's greater than 0.5 or not. Since we
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want to do the whole calculation in integer arithmetic, it's
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simpler to do:
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(1) divide by (10**n)/2
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(2) round to nearest multiple of 2 (multiple of 4 in case of tie)
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(3) multiply result by (10**n)/2.
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Then all we need to know about the fractional part of the quotient
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arising in step (2) is whether it's zero or not.
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Doing both a multiplication and division is wasteful, and is easily
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avoided if we just figure out how much to adjust the original input
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by to do the rounding.
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Here's the whole algorithm expressed in Python.
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def round(self, ndigits = None):
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"""round(int, int) -> int"""
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if ndigits is None or ndigits >= 0:
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return self
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pow = 10**-ndigits >> 1
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q, r = divmod(self, pow)
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self -= r
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if (q & 1 != 0):
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if (q & 2 == r == 0):
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self -= pow
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else:
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self += pow
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return self
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*/
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if (!PyArg_ParseTuple(args, "|O", &o_ndigits))
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return NULL;
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if (o_ndigits == NULL)
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return long_long(self);
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/* If called with two args, defer to float.__round__(). */
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x = PyLong_AsDouble(self);
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if (x == -1.0 && PyErr_Occurred())
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ndigits = (PyLongObject *)PyNumber_Index(o_ndigits);
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if (ndigits == NULL)
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return NULL;
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self = PyFloat_FromDouble(x);
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if (self == NULL)
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return NULL;
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res = PyObject_CallMethod(self, "__round__", "i", ndigits);
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if (Py_SIZE(ndigits) >= 0) {
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Py_DECREF(ndigits);
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return long_long(self);
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}
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Py_INCREF(self); /* to keep refcounting simple */
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/* we now own references to self, ndigits */
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/* pow = 10 ** -ndigits >> 1 */
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pow = (PyLongObject *)PyLong_FromLong(10L);
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if (pow == NULL)
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goto error;
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temp = long_neg(ndigits);
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Py_DECREF(ndigits);
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ndigits = (PyLongObject *)temp;
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if (ndigits == NULL)
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goto error;
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temp = long_pow((PyObject *)pow, (PyObject *)ndigits, Py_None);
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Py_DECREF(pow);
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pow = (PyLongObject *)temp;
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if (pow == NULL)
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goto error;
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assert(PyLong_Check(pow)); /* check long_pow returned a long */
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one = (PyLongObject *)PyLong_FromLong(1L);
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if (one == NULL)
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goto error;
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temp = long_rshift(pow, one);
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Py_DECREF(one);
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Py_DECREF(pow);
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pow = (PyLongObject *)temp;
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if (pow == NULL)
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goto error;
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/* q, r = divmod(self, pow) */
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errcode = l_divmod((PyLongObject *)self, pow, &q, &r);
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if (errcode == -1)
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goto error;
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/* self -= r */
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temp = long_sub((PyLongObject *)self, r);
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Py_DECREF(self);
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return res;
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#undef UNDEF_NDIGITS
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self = temp;
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if (self == NULL)
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goto error;
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/* get value of quotient modulo 4 */
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if (Py_SIZE(q) == 0)
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q_mod_4 = 0;
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else if (Py_SIZE(q) > 0)
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q_mod_4 = q->ob_digit[0] & 3;
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else
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q_mod_4 = (PyLong_BASE-q->ob_digit[0]) & 3;
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if ((q_mod_4 & 1) == 1) {
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/* q is odd; round self up or down by adding or subtracting pow */
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if (q_mod_4 == 1 && Py_SIZE(r) == 0)
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temp = (PyObject *)long_sub((PyLongObject *)self, pow);
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else
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temp = (PyObject *)long_add((PyLongObject *)self, pow);
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Py_DECREF(self);
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self = temp;
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if (self == NULL)
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goto error;
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}
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Py_DECREF(q);
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Py_DECREF(r);
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Py_DECREF(pow);
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Py_DECREF(ndigits);
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return self;
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error:
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Py_XDECREF(q);
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Py_XDECREF(r);
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Py_XDECREF(pow);
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Py_XDECREF(self);
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Py_XDECREF(ndigits);
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return NULL;
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}
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static PyObject *
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@ -3773,8 +3881,8 @@ static PyMethodDef long_methods[] = {
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{"__ceil__", (PyCFunction)long_long, METH_NOARGS,
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"Ceiling of an Integral returns itself."},
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{"__round__", (PyCFunction)long_round, METH_VARARGS,
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"Rounding an Integral returns itself.\n"
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"Rounding with an ndigits arguments defers to float.__round__."},
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"Rounding an Integral returns itself.\n"
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"Rounding with an ndigits argument also returns an integer."},
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{"__getnewargs__", (PyCFunction)long_getnewargs, METH_NOARGS},
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{"__format__", (PyCFunction)long__format__, METH_VARARGS},
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{"__sizeof__", (PyCFunction)long_sizeof, METH_NOARGS,
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@ -1717,15 +1717,14 @@ For most object types, eval(repr(object)) == object.");
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static PyObject *
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builtin_round(PyObject *self, PyObject *args, PyObject *kwds)
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{
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#define UNDEF_NDIGITS (-0x7fffffff) /* Unlikely ndigits value */
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static PyObject *round_str = NULL;
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int ndigits = UNDEF_NDIGITS;
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PyObject *ndigits = NULL;
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static char *kwlist[] = {"number", "ndigits", 0};
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PyObject *number, *round;
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if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|i:round",
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kwlist, &number, &ndigits))
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return NULL;
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if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|O:round",
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kwlist, &number, &ndigits))
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return NULL;
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if (Py_TYPE(number)->tp_dict == NULL) {
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if (PyType_Ready(Py_TYPE(number)) < 0)
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@ -1746,15 +1745,14 @@ builtin_round(PyObject *self, PyObject *args, PyObject *kwds)
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return NULL;
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}
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if (ndigits == UNDEF_NDIGITS)
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return PyObject_CallFunction(round, "O", number);
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if (ndigits == NULL)
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return PyObject_CallFunction(round, "O", number);
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else
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return PyObject_CallFunction(round, "Oi", number, ndigits);
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#undef UNDEF_NDIGITS
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return PyObject_CallFunction(round, "OO", number, ndigits);
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}
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PyDoc_STRVAR(round_doc,
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"round(number[, ndigits]) -> floating point number\n\
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"round(number[, ndigits]) -> number\n\
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\n\
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Round a number to a given precision in decimal digits (default 0 digits).\n\
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This returns an int when called with one argument, otherwise the\n\
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