[Python-checkins] r60377 - in python/trunk: Lib/rational.py Lib/test/test_builtin.py Objects/floatobject.c
jeffrey.yasskin
python-checkins at python.org
Mon Jan 28 00:08:47 CET 2008
Author: jeffrey.yasskin
Date: Mon Jan 28 00:08:46 2008
New Revision: 60377
Modified:
python/trunk/Lib/rational.py
python/trunk/Lib/test/test_builtin.py
python/trunk/Objects/floatobject.c
Log:
Moved Rational._binary_float_to_ratio() to float.as_integer_ratio() because
it's useful outside of rational numbers.
This is my first C code that had to do anything significant. Please be more
careful when looking over it.
Modified: python/trunk/Lib/rational.py
==============================================================================
--- python/trunk/Lib/rational.py (original)
+++ python/trunk/Lib/rational.py Mon Jan 28 00:08:46 2008
@@ -25,60 +25,6 @@
return a
-def _binary_float_to_ratio(x):
- """x -> (top, bot), a pair of ints s.t. x = top/bot.
-
- The conversion is done exactly, without rounding.
- bot > 0 guaranteed.
- Some form of binary fp is assumed.
- Pass NaNs or infinities at your own risk.
-
- >>> _binary_float_to_ratio(10.0)
- (10, 1)
- >>> _binary_float_to_ratio(0.0)
- (0, 1)
- >>> _binary_float_to_ratio(-.25)
- (-1, 4)
- """
- # XXX Move this to floatobject.c with a name like
- # float.as_integer_ratio()
-
- if x == 0:
- return 0, 1
- f, e = math.frexp(x)
- signbit = 1
- if f < 0:
- f = -f
- signbit = -1
- assert 0.5 <= f < 1.0
- # x = signbit * f * 2**e exactly
-
- # Suck up CHUNK bits at a time; 28 is enough so that we suck
- # up all bits in 2 iterations for all known binary double-
- # precision formats, and small enough to fit in an int.
- CHUNK = 28
- top = 0
- # invariant: x = signbit * (top + f) * 2**e exactly
- while f:
- f = math.ldexp(f, CHUNK)
- digit = trunc(f)
- assert digit >> CHUNK == 0
- top = (top << CHUNK) | digit
- f = f - digit
- assert 0.0 <= f < 1.0
- e = e - CHUNK
- assert top
-
- # Add in the sign bit.
- top = signbit * top
-
- # now x = top * 2**e exactly; fold in 2**e
- if e>0:
- return (top * 2**e, 1)
- else:
- return (top, 2 ** -e)
-
-
_RATIONAL_FORMAT = re.compile(
r'^\s*(?P<sign>[-+]?)(?P<num>\d+)'
r'(?:/(?P<denom>\d+)|\.(?P<decimal>\d+))?\s*$')
@@ -163,7 +109,7 @@
(cls.__name__, f, type(f).__name__))
if math.isnan(f) or math.isinf(f):
raise TypeError("Cannot convert %r to %s." % (f, cls.__name__))
- return cls(*_binary_float_to_ratio(f))
+ return cls(*f.as_integer_ratio())
@classmethod
def from_decimal(cls, dec):
Modified: python/trunk/Lib/test/test_builtin.py
==============================================================================
--- python/trunk/Lib/test/test_builtin.py (original)
+++ python/trunk/Lib/test/test_builtin.py Mon Jan 28 00:08:46 2008
@@ -5,7 +5,7 @@
run_unittest, run_with_locale
from operator import neg
-import sys, warnings, cStringIO, random, UserDict
+import sys, warnings, cStringIO, random, rational, UserDict
warnings.filterwarnings("ignore", "hex../oct.. of negative int",
FutureWarning, __name__)
warnings.filterwarnings("ignore", "integer argument expected",
@@ -688,6 +688,25 @@
self.assertAlmostEqual(float(Foo3(21)), 42.)
self.assertRaises(TypeError, float, Foo4(42))
+ def test_floatasratio(self):
+ R = rational.Rational
+ self.assertEqual(R(0, 1),
+ R(*float(0.0).as_integer_ratio()))
+ self.assertEqual(R(5, 2),
+ R(*float(2.5).as_integer_ratio()))
+ self.assertEqual(R(1, 2),
+ R(*float(0.5).as_integer_ratio()))
+ self.assertEqual(R(4728779608739021, 2251799813685248),
+ R(*float(2.1).as_integer_ratio()))
+ self.assertEqual(R(-4728779608739021, 2251799813685248),
+ R(*float(-2.1).as_integer_ratio()))
+ self.assertEqual(R(-2100, 1),
+ R(*float(-2100.0).as_integer_ratio()))
+
+ self.assertRaises(OverflowError, float('inf').as_integer_ratio)
+ self.assertRaises(OverflowError, float('-inf').as_integer_ratio)
+ self.assertRaises(ValueError, float('nan').as_integer_ratio)
+
def test_getattr(self):
import sys
self.assert_(getattr(sys, 'stdout') is sys.stdout)
Modified: python/trunk/Objects/floatobject.c
==============================================================================
--- python/trunk/Objects/floatobject.c (original)
+++ python/trunk/Objects/floatobject.c Mon Jan 28 00:08:46 2008
@@ -1161,6 +1161,163 @@
return v;
}
+static PyObject *
+float_as_integer_ratio(PyObject *v)
+{
+ double self;
+ double float_part;
+ int exponent;
+ int is_negative;
+ const int chunk_size = 28;
+ PyObject *prev;
+ PyObject *py_chunk = NULL;
+ PyObject *py_exponent = NULL;
+ PyObject *numerator = NULL;
+ PyObject *denominator = NULL;
+ PyObject *result_pair = NULL;
+ PyNumberMethods *long_methods;
+
+#define INPLACE_UPDATE(obj, call) \
+ prev = obj; \
+ obj = call; \
+ Py_DECREF(prev); \
+
+ CONVERT_TO_DOUBLE(v, self);
+
+ if (Py_IS_INFINITY(self)) {
+ PyErr_SetString(PyExc_OverflowError,
+ "Cannot pass infinity to float.as_integer_ratio.");
+ return NULL;
+ }
+#ifdef Py_NAN
+ if (Py_IS_NAN(self)) {
+ PyErr_SetString(PyExc_ValueError,
+ "Cannot pass nan to float.as_integer_ratio.");
+ return NULL;
+ }
+#endif
+
+ if (self == 0) {
+ numerator = PyInt_FromLong(0);
+ if (numerator == NULL) goto error;
+ denominator = PyInt_FromLong(1);
+ if (denominator == NULL) goto error;
+ result_pair = PyTuple_Pack(2, numerator, denominator);
+ /* Hand ownership over to the tuple. If the tuple
+ wasn't created successfully, we want to delete the
+ ints anyway. */
+ Py_DECREF(numerator);
+ Py_DECREF(denominator);
+ return result_pair;
+ }
+
+ /* XXX: Could perhaps handle FLT_RADIX!=2 by using ilogb and
+ scalbn, but those may not be in C89. */
+ PyFPE_START_PROTECT("as_integer_ratio", goto error);
+ float_part = frexp(self, &exponent);
+ is_negative = 0;
+ if (float_part < 0) {
+ float_part = -float_part;
+ is_negative = 1;
+ /* 0.5 <= float_part < 1.0 */
+ }
+ PyFPE_END_PROTECT(float_part);
+ /* abs(self) == float_part * 2**exponent exactly */
+
+ /* Suck up chunk_size bits at a time; 28 is enough so that we
+ suck up all bits in 2 iterations for all known binary
+ double-precision formats, and small enough to fit in a
+ long. */
+ numerator = PyLong_FromLong(0);
+ if (numerator == NULL) goto error;
+
+ long_methods = PyLong_Type.tp_as_number;
+
+ py_chunk = PyLong_FromLong(chunk_size);
+ if (py_chunk == NULL) goto error;
+
+ while (float_part != 0) {
+ /* invariant: abs(self) ==
+ (numerator + float_part) * 2**exponent exactly */
+ long digit;
+ PyObject *py_digit;
+
+ PyFPE_START_PROTECT("as_integer_ratio", goto error);
+ /* Pull chunk_size bits out of float_part, into digits. */
+ float_part = ldexp(float_part, chunk_size);
+ digit = (long)float_part;
+ float_part -= digit;
+ /* 0 <= float_part < 1 */
+ exponent -= chunk_size;
+ PyFPE_END_PROTECT(float_part);
+
+ /* Shift digits into numerator. */
+ // numerator <<= chunk_size
+ INPLACE_UPDATE(numerator,
+ long_methods->nb_lshift(numerator, py_chunk));
+ if (numerator == NULL) goto error;
+
+ // numerator |= digit
+ py_digit = PyLong_FromLong(digit);
+ if (py_digit == NULL) goto error;
+ INPLACE_UPDATE(numerator,
+ long_methods->nb_or(numerator, py_digit));
+ Py_DECREF(py_digit);
+ if (numerator == NULL) goto error;
+ }
+
+ /* Add in the sign bit. */
+ if (is_negative) {
+ INPLACE_UPDATE(numerator,
+ long_methods->nb_negative(numerator));
+ if (numerator == NULL) goto error;
+ }
+
+ /* now self = numerator * 2**exponent exactly; fold in 2**exponent */
+ denominator = PyLong_FromLong(1);
+ py_exponent = PyLong_FromLong(labs(exponent));
+ if (py_exponent == NULL) goto error;
+ INPLACE_UPDATE(py_exponent,
+ long_methods->nb_lshift(denominator, py_exponent));
+ if (py_exponent == NULL) goto error;
+ if (exponent > 0) {
+ INPLACE_UPDATE(numerator,
+ long_methods->nb_multiply(numerator,
+ py_exponent));
+ if (numerator == NULL) goto error;
+ }
+ else {
+ Py_DECREF(denominator);
+ denominator = py_exponent;
+ py_exponent = NULL;
+ }
+
+ result_pair = PyTuple_Pack(2, numerator, denominator);
+
+#undef INPLACE_UPDATE
+error:
+ Py_XDECREF(py_exponent);
+ Py_XDECREF(py_chunk);
+ Py_XDECREF(denominator);
+ Py_XDECREF(numerator);
+ return result_pair;
+}
+
+PyDoc_STRVAR(float_as_integer_ratio_doc,
+"float.as_integer_ratio() -> (int, int)\n"
+"\n"
+"Returns a pair of integers, not necessarily in lowest terms, whose\n"
+"ratio is exactly equal to the original float. This method raises an\n"
+"OverflowError on infinities and a ValueError on nans. The resulting\n"
+"denominator will be positive.\n"
+"\n"
+">>> (10.0).as_integer_ratio()\n"
+"(167772160L, 16777216L)\n"
+">>> (0.0).as_integer_ratio()\n"
+"(0, 1)\n"
+">>> (-.25).as_integer_ratio()\n"
+"(-134217728L, 536870912L)");
+
static PyObject *
float_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds);
@@ -1349,6 +1506,8 @@
"Returns self, the complex conjugate of any float."},
{"__trunc__", (PyCFunction)float_trunc, METH_NOARGS,
"Returns the Integral closest to x between 0 and x."},
+ {"as_integer_ratio", (PyCFunction)float_as_integer_ratio, METH_NOARGS,
+ float_as_integer_ratio_doc},
{"__getnewargs__", (PyCFunction)float_getnewargs, METH_NOARGS},
{"__getformat__", (PyCFunction)float_getformat,
METH_O|METH_CLASS, float_getformat_doc},
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