[Python-checkins] r69068 - in python/branches/py3k: Lib/test/test_builtin.py Lib/test/test_long.py Misc/NEWS Objects/longobject.c Python/bltinmodule.c
mark.dickinson
python-checkins at python.org
Wed Jan 28 22:25:58 CET 2009
Author: mark.dickinson
Date: Wed Jan 28 22:25:58 2009
New Revision: 69068
Log:
Issue #4707: round(x, n) now returns an integer when x is an integer.
Previously it returned a float.
Modified:
python/branches/py3k/Lib/test/test_builtin.py
python/branches/py3k/Lib/test/test_long.py
python/branches/py3k/Misc/NEWS
python/branches/py3k/Objects/longobject.c
python/branches/py3k/Python/bltinmodule.c
Modified: python/branches/py3k/Lib/test/test_builtin.py
==============================================================================
--- python/branches/py3k/Lib/test/test_builtin.py (original)
+++ python/branches/py3k/Lib/test/test_builtin.py Wed Jan 28 22:25:58 2009
@@ -1068,9 +1068,9 @@
self.assertEqual(round(8), 8)
self.assertEqual(round(-8), -8)
self.assertEqual(type(round(0)), int)
- self.assertEqual(type(round(-8, -1)), float)
- self.assertEqual(type(round(-8, 0)), float)
- self.assertEqual(type(round(-8, 1)), float)
+ self.assertEqual(type(round(-8, -1)), int)
+ self.assertEqual(type(round(-8, 0)), int)
+ self.assertEqual(type(round(-8, 1)), int)
# test new kwargs
self.assertEqual(round(number=-8.0, ndigits=-1), -10.0)
Modified: python/branches/py3k/Lib/test/test_long.py
==============================================================================
--- python/branches/py3k/Lib/test/test_long.py (original)
+++ python/branches/py3k/Lib/test/test_long.py Wed Jan 28 22:25:58 2009
@@ -896,6 +896,81 @@
self.assertEqual((a+1).bit_length(), i+1)
self.assertEqual((-a-1).bit_length(), i+1)
+ def test_round(self):
+ # check round-half-even algorithm. For round to nearest ten;
+ # rounding map is invariant under adding multiples of 20
+ test_dict = {0:0, 1:0, 2:0, 3:0, 4:0, 5:0,
+ 6:10, 7:10, 8:10, 9:10, 10:10, 11:10, 12:10, 13:10, 14:10,
+ 15:20, 16:20, 17:20, 18:20, 19:20}
+ for offset in range(-520, 520, 20):
+ for k, v in test_dict.items():
+ got = round(k+offset, -1)
+ expected = v+offset
+ self.assertEqual(got, expected)
+ self.assert_(type(got) is int)
+
+ # larger second argument
+ self.assertEqual(round(-150, -2), -200)
+ self.assertEqual(round(-149, -2), -100)
+ self.assertEqual(round(-51, -2), -100)
+ self.assertEqual(round(-50, -2), 0)
+ self.assertEqual(round(-49, -2), 0)
+ self.assertEqual(round(-1, -2), 0)
+ self.assertEqual(round(0, -2), 0)
+ self.assertEqual(round(1, -2), 0)
+ self.assertEqual(round(49, -2), 0)
+ self.assertEqual(round(50, -2), 0)
+ self.assertEqual(round(51, -2), 100)
+ self.assertEqual(round(149, -2), 100)
+ self.assertEqual(round(150, -2), 200)
+ self.assertEqual(round(250, -2), 200)
+ self.assertEqual(round(251, -2), 300)
+ self.assertEqual(round(172500, -3), 172000)
+ self.assertEqual(round(173500, -3), 174000)
+ self.assertEqual(round(31415926535, -1), 31415926540)
+ self.assertEqual(round(31415926535, -2), 31415926500)
+ self.assertEqual(round(31415926535, -3), 31415927000)
+ self.assertEqual(round(31415926535, -4), 31415930000)
+ self.assertEqual(round(31415926535, -5), 31415900000)
+ self.assertEqual(round(31415926535, -6), 31416000000)
+ self.assertEqual(round(31415926535, -7), 31420000000)
+ self.assertEqual(round(31415926535, -8), 31400000000)
+ self.assertEqual(round(31415926535, -9), 31000000000)
+ self.assertEqual(round(31415926535, -10), 30000000000)
+ self.assertEqual(round(31415926535, -11), 0)
+ self.assertEqual(round(31415926535, -12), 0)
+ self.assertEqual(round(31415926535, -999), 0)
+
+ # should get correct results even for huge inputs
+ for k in range(10, 100):
+ got = round(10**k + 324678, -3)
+ expect = 10**k + 325000
+ self.assertEqual(got, expect)
+ self.assert_(type(got) is int)
+
+ # nonnegative second argument: round(x, n) should just return x
+ for n in range(5):
+ for i in range(100):
+ x = random.randrange(-10000, 10000)
+ got = round(x, n)
+ self.assertEqual(got, x)
+ self.assert_(type(got) is int)
+ for huge_n in 2**31-1, 2**31, 2**63-1, 2**63, 2**100, 10**100:
+ self.assertEqual(round(8979323, huge_n), 8979323)
+
+ # omitted second argument
+ for i in range(100):
+ x = random.randrange(-10000, 10000)
+ got = round(x)
+ self.assertEqual(got, x)
+ self.assert_(type(got) is int)
+
+ # bad second argument
+ bad_exponents = ('brian', 2.0, 0j, None)
+ for e in bad_exponents:
+ self.assertRaises(TypeError, round, 3, e)
+
+
def test_main():
support.run_unittest(LongTest)
Modified: python/branches/py3k/Misc/NEWS
==============================================================================
--- python/branches/py3k/Misc/NEWS (original)
+++ python/branches/py3k/Misc/NEWS Wed Jan 28 22:25:58 2009
@@ -12,6 +12,9 @@
Core and Builtins
-----------------
+- Issue #4707: round(x, n) now returns an integer if x is an integer.
+ Previously it returned a float.
+
- Issue #4753: By enabling a configure option named '--with-computed-gotos'
on compilers that support it (notably: gcc, SunPro, icc), the bytecode
evaluation loop is compiled with a new dispatch mechanism which gives
Modified: python/branches/py3k/Objects/longobject.c
==============================================================================
--- python/branches/py3k/Objects/longobject.c (original)
+++ python/branches/py3k/Objects/longobject.c Wed Jan 28 22:25:58 2009
@@ -3643,32 +3643,140 @@
PyUnicode_GET_SIZE(format_spec));
}
-
static PyObject *
long_round(PyObject *self, PyObject *args)
{
-#define UNDEF_NDIGITS (-0x7fffffff) /* Unlikely ndigits value */
- int ndigits = UNDEF_NDIGITS;
- double x;
- PyObject *res;
-
- if (!PyArg_ParseTuple(args, "|i", &ndigits))
- return NULL;
+ PyObject *o_ndigits=NULL, *temp;
+ PyLongObject *pow=NULL, *q=NULL, *r=NULL, *ndigits=NULL, *one;
+ int errcode;
+ digit q_mod_4;
+
+ /* Notes on the algorithm: to round to the nearest 10**n (n positive),
+ the straightforward method is:
+
+ (1) divide by 10**n
+ (2) round to nearest integer (round to even in case of tie)
+ (3) multiply result by 10**n.
+
+ But the rounding step involves examining the fractional part of the
+ quotient to see whether it's greater than 0.5 or not. Since we
+ want to do the whole calculation in integer arithmetic, it's
+ simpler to do:
+
+ (1) divide by (10**n)/2
+ (2) round to nearest multiple of 2 (multiple of 4 in case of tie)
+ (3) multiply result by (10**n)/2.
+
+ Then all we need to know about the fractional part of the quotient
+ arising in step (2) is whether it's zero or not.
+
+ Doing both a multiplication and division is wasteful, and is easily
+ avoided if we just figure out how much to adjust the original input
+ by to do the rounding.
+
+ Here's the whole algorithm expressed in Python.
+
+ def round(self, ndigits = None):
+ """round(int, int) -> int"""
+ if ndigits is None or ndigits >= 0:
+ return self
+ pow = 10**-ndigits >> 1
+ q, r = divmod(self, pow)
+ self -= r
+ if (q & 1 != 0):
+ if (q & 2 == r == 0):
+ self -= pow
+ else:
+ self += pow
+ return self
- if (ndigits == UNDEF_NDIGITS)
+ */
+ if (!PyArg_ParseTuple(args, "|O", &o_ndigits))
+ return NULL;
+ if (o_ndigits == NULL)
return long_long(self);
- /* If called with two args, defer to float.__round__(). */
- x = PyLong_AsDouble(self);
- if (x == -1.0 && PyErr_Occurred())
+ ndigits = (PyLongObject *)PyNumber_Index(o_ndigits);
+ if (ndigits == NULL)
return NULL;
- self = PyFloat_FromDouble(x);
- if (self == NULL)
- return NULL;
- res = PyObject_CallMethod(self, "__round__", "i", ndigits);
+
+ if (Py_SIZE(ndigits) >= 0) {
+ Py_DECREF(ndigits);
+ return long_long(self);
+ }
+
+ Py_INCREF(self); /* to keep refcounting simple */
+ /* we now own references to self, ndigits */
+
+ /* pow = 10 ** -ndigits >> 1 */
+ pow = (PyLongObject *)PyLong_FromLong(10L);
+ if (pow == NULL)
+ goto error;
+ temp = long_neg(ndigits);
+ Py_DECREF(ndigits);
+ ndigits = (PyLongObject *)temp;
+ if (ndigits == NULL)
+ goto error;
+ temp = long_pow((PyObject *)pow, (PyObject *)ndigits, Py_None);
+ Py_DECREF(pow);
+ pow = (PyLongObject *)temp;
+ if (pow == NULL)
+ goto error;
+ assert(PyLong_Check(pow)); /* check long_pow returned a long */
+ one = (PyLongObject *)PyLong_FromLong(1L);
+ if (one == NULL)
+ goto error;
+ temp = long_rshift(pow, one);
+ Py_DECREF(one);
+ Py_DECREF(pow);
+ pow = (PyLongObject *)temp;
+ if (pow == NULL)
+ goto error;
+
+ /* q, r = divmod(self, pow) */
+ errcode = l_divmod((PyLongObject *)self, pow, &q, &r);
+ if (errcode == -1)
+ goto error;
+
+ /* self -= r */
+ temp = long_sub((PyLongObject *)self, r);
Py_DECREF(self);
- return res;
-#undef UNDEF_NDIGITS
+ self = temp;
+ if (self == NULL)
+ goto error;
+
+ /* get value of quotient modulo 4 */
+ if (Py_SIZE(q) == 0)
+ q_mod_4 = 0;
+ else if (Py_SIZE(q) > 0)
+ q_mod_4 = q->ob_digit[0] & 3;
+ else
+ q_mod_4 = (PyLong_BASE-q->ob_digit[0]) & 3;
+
+ if ((q_mod_4 & 1) == 1) {
+ /* q is odd; round self up or down by adding or subtracting pow */
+ if (q_mod_4 == 1 && Py_SIZE(r) == 0)
+ temp = (PyObject *)long_sub((PyLongObject *)self, pow);
+ else
+ temp = (PyObject *)long_add((PyLongObject *)self, pow);
+ Py_DECREF(self);
+ self = temp;
+ if (self == NULL)
+ goto error;
+ }
+ Py_DECREF(q);
+ Py_DECREF(r);
+ Py_DECREF(pow);
+ Py_DECREF(ndigits);
+ return self;
+
+ error:
+ Py_XDECREF(q);
+ Py_XDECREF(r);
+ Py_XDECREF(pow);
+ Py_XDECREF(self);
+ Py_XDECREF(ndigits);
+ return NULL;
}
static PyObject *
@@ -3773,8 +3881,8 @@
{"__ceil__", (PyCFunction)long_long, METH_NOARGS,
"Ceiling of an Integral returns itself."},
{"__round__", (PyCFunction)long_round, METH_VARARGS,
- "Rounding an Integral returns itself.\n"
- "Rounding with an ndigits arguments defers to float.__round__."},
+ "Rounding an Integral returns itself.\n"
+ "Rounding with an ndigits argument also returns an integer."},
{"__getnewargs__", (PyCFunction)long_getnewargs, METH_NOARGS},
{"__format__", (PyCFunction)long__format__, METH_VARARGS},
{"__sizeof__", (PyCFunction)long_sizeof, METH_NOARGS,
Modified: python/branches/py3k/Python/bltinmodule.c
==============================================================================
--- python/branches/py3k/Python/bltinmodule.c (original)
+++ python/branches/py3k/Python/bltinmodule.c Wed Jan 28 22:25:58 2009
@@ -1717,15 +1717,14 @@
static PyObject *
builtin_round(PyObject *self, PyObject *args, PyObject *kwds)
{
-#define UNDEF_NDIGITS (-0x7fffffff) /* Unlikely ndigits value */
static PyObject *round_str = NULL;
- int ndigits = UNDEF_NDIGITS;
+ PyObject *ndigits = NULL;
static char *kwlist[] = {"number", "ndigits", 0};
PyObject *number, *round;
- if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|i:round",
- kwlist, &number, &ndigits))
- return NULL;
+ if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|O:round",
+ kwlist, &number, &ndigits))
+ return NULL;
if (Py_TYPE(number)->tp_dict == NULL) {
if (PyType_Ready(Py_TYPE(number)) < 0)
@@ -1746,15 +1745,14 @@
return NULL;
}
- if (ndigits == UNDEF_NDIGITS)
- return PyObject_CallFunction(round, "O", number);
+ if (ndigits == NULL)
+ return PyObject_CallFunction(round, "O", number);
else
- return PyObject_CallFunction(round, "Oi", number, ndigits);
-#undef UNDEF_NDIGITS
+ return PyObject_CallFunction(round, "OO", number, ndigits);
}
PyDoc_STRVAR(round_doc,
-"round(number[, ndigits]) -> floating point number\n\
+"round(number[, ndigits]) -> number\n\
\n\
Round a number to a given precision in decimal digits (default 0 digits).\n\
This returns an int when called with one argument, otherwise the\n\
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