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Apr 19, 2019
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ENH: Implement np.floating.as_integer_ratio #10741

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79799b3
ENH: Implement `np.floating.as_integer_ratio`
eric-wieser Nov 5, 2017
4bebf05
TST: use smaller tests for PR 10741.
tylerjereddy Apr 12, 2019
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6 changes: 6 additions & 0 deletions doc/release/1.17.0-notes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -129,6 +129,12 @@ New mode "empty" for ``np.pad``
This mode pads an array to a desired shape without initializing the new
entries.

Floating point scalars implement ``as_integer_ratio`` to match the builtin float
--------------------------------------------------------------------------------
This returns a (numerator, denominator) pair, which can be used to construct a
`fractions.Fraction`.


Improvements
============

Expand Down
18 changes: 18 additions & 0 deletions numpy/core/_add_newdocs.py
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Expand Up @@ -6903,3 +6903,21 @@ def add_newdoc_for_scalar_type(obj, fixed_aliases, doc):
"""
Any Python object.
""")

# TODO: work out how to put this on the base class, np.floating
for float_name in ('half', 'single', 'double', 'longdouble'):
add_newdoc('numpy.core.numerictypes', float_name, ('as_integer_ratio',
"""
{ftype}.as_integer_ratio() -> (int, int)

Return a pair of integers, whose ratio is exactly equal to the original
floating point number, and with a positive denominator.
Raise OverflowError on infinities and a ValueError on NaNs.

>>> np.{ftype}(10.0).as_integer_ratio()
(10, 1)
>>> np.{ftype}(0.0).as_integer_ratio()
(0, 1)
>>> np.{ftype}(-.25).as_integer_ratio()
(-1, 4)
""".format(ftype=float_name)))
106 changes: 106 additions & 0 deletions numpy/core/src/multiarray/scalartypes.c.src
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Expand Up @@ -1993,6 +1993,92 @@ static PyObject *
}
/**end repeat**/

/**begin repeat
* #name = half, float, double, longdouble#
* #Name = Half, Float, Double, LongDouble#
* #is_half = 1,0,0,0#
* #c = f, f, , l#
* #convert = PyLong_FromDouble, PyLong_FromDouble, PyLong_FromDouble,
* npy_longdouble_to_PyLong#
* #
*/
/* Heavily copied from the builtin float.as_integer_ratio */
static PyObject *
@name@_as_integer_ratio(PyObject *self)
{
#if @is_half@
npy_double val = npy_half_to_double(PyArrayScalar_VAL(self, @Name@));
npy_double frac;
#else
npy_@name@ val = PyArrayScalar_VAL(self, @Name@);
npy_@name@ frac;
#endif
int exponent;
int i;

PyObject *py_exponent = NULL;
PyObject *numerator = NULL;
PyObject *denominator = NULL;
PyObject *result_pair = NULL;
PyNumberMethods *long_methods = PyLong_Type.tp_as_number;

if (npy_isnan(val)) {
PyErr_SetString(PyExc_ValueError,
"cannot convert NaN to integer ratio");
return NULL;
}
if (!npy_isfinite(val)) {
PyErr_SetString(PyExc_OverflowError,
"cannot convert Infinity to integer ratio");
return NULL;
}

frac = npy_frexp@c@(val, &exponent); /* val == frac * 2**exponent exactly */

/* This relies on the floating point type being base 2 to converge */
for (i = 0; frac != npy_floor@c@(frac); i++) {
frac *= 2.0;
exponent--;
}

/* self == frac * 2**exponent exactly and frac is integral. */
numerator = @convert@(frac);
if (numerator == NULL)
goto error;
denominator = PyLong_FromLong(1);
if (denominator == NULL)
goto error;
py_exponent = PyLong_FromLong(exponent < 0 ? -exponent : exponent);
if (py_exponent == NULL)
goto error;

/* fold in 2**exponent */
if (exponent > 0) {
PyObject *temp = long_methods->nb_lshift(numerator, py_exponent);
if (temp == NULL)
goto error;
Py_DECREF(numerator);
numerator = temp;
}
else {
PyObject *temp = long_methods->nb_lshift(denominator, py_exponent);
if (temp == NULL)
goto error;
Py_DECREF(denominator);
denominator = temp;
}

result_pair = PyTuple_Pack(2, numerator, denominator);

error:
Py_XDECREF(py_exponent);
Py_XDECREF(denominator);
Py_XDECREF(numerator);
return result_pair;
}
/**end repeat**/


/*
* need to fill in doc-strings for these methods on import -- copy from
* array docstrings
Expand Down Expand Up @@ -2256,6 +2342,17 @@ static PyMethodDef @name@type_methods[] = {
};
/**end repeat**/

/**begin repeat
* #name = half,float,double,longdouble#
*/
static PyMethodDef @name@type_methods[] = {
{"as_integer_ratio",
(PyCFunction)@name@_as_integer_ratio,
METH_NOARGS, NULL},
{NULL, NULL, 0, NULL}
};
/**end repeat**/

/************* As_mapping functions for void array scalar ************/

static Py_ssize_t
Expand Down Expand Up @@ -4311,6 +4408,15 @@ initialize_numeric_types(void)

/**end repeat**/

/**begin repeat
* #name = half, float, double, longdouble#
* #Name = Half, Float, Double, LongDouble#
*/

Py@Name@ArrType_Type.tp_methods = @name@type_methods;

/**end repeat**/

#if (NPY_SIZEOF_INT != NPY_SIZEOF_LONG) || defined(NPY_PY3K)
/* We won't be inheriting from Python Int type. */
PyIntArrType_Type.tp_hash = int_arrtype_hash;
Expand Down
109 changes: 109 additions & 0 deletions numpy/core/tests/test_scalar_methods.py
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@@ -0,0 +1,109 @@
"""
Test the scalar constructors, which also do type-coercion
"""
from __future__ import division, absolute_import, print_function

import os
import fractions
import platform

import pytest
import numpy as np

from numpy.testing import (
run_module_suite,
assert_equal, assert_almost_equal, assert_raises, assert_warns,
dec
)

class TestAsIntegerRatio(object):
# derived in part from the cpython test "test_floatasratio"

@pytest.mark.parametrize("ftype", [
np.half, np.single, np.double, np.longdouble])
@pytest.mark.parametrize("f, ratio", [
(0.875, (7, 8)),
(-0.875, (-7, 8)),
(0.0, (0, 1)),
(11.5, (23, 2)),
])
def test_small(self, ftype, f, ratio):
assert_equal(ftype(f).as_integer_ratio(), ratio)

@pytest.mark.parametrize("ftype", [
np.half, np.single, np.double, np.longdouble])
def test_simple_fractions(self, ftype):
R = fractions.Fraction
assert_equal(R(0, 1),
R(*ftype(0.0).as_integer_ratio()))
assert_equal(R(5, 2),
R(*ftype(2.5).as_integer_ratio()))
assert_equal(R(1, 2),
R(*ftype(0.5).as_integer_ratio()))
assert_equal(R(-2100, 1),
R(*ftype(-2100.0).as_integer_ratio()))

@pytest.mark.parametrize("ftype", [
np.half, np.single, np.double, np.longdouble])
def test_errors(self, ftype):
assert_raises(OverflowError, ftype('inf').as_integer_ratio)
assert_raises(OverflowError, ftype('-inf').as_integer_ratio)
assert_raises(ValueError, ftype('nan').as_integer_ratio)

def test_against_known_values(self):
R = fractions.Fraction
assert_equal(R(1075, 512),
R(*np.half(2.1).as_integer_ratio()))
assert_equal(R(-1075, 512),
R(*np.half(-2.1).as_integer_ratio()))
assert_equal(R(4404019, 2097152),
R(*np.single(2.1).as_integer_ratio()))
assert_equal(R(-4404019, 2097152),
R(*np.single(-2.1).as_integer_ratio()))
assert_equal(R(4728779608739021, 2251799813685248),
R(*np.double(2.1).as_integer_ratio()))
assert_equal(R(-4728779608739021, 2251799813685248),
R(*np.double(-2.1).as_integer_ratio()))
# longdouble is platform depedent

@pytest.mark.parametrize("ftype, frac_vals, exp_vals", [
# dtype test cases generated using hypothesis
# first five generated cases per dtype
(np.half, [0.0, 0.01154830649280303, 0.31082276347447274,
0.527350517124794, 0.8308562335072596],
[0, 1, 0, -8, 12]),
(np.single, [0.0, 0.09248576989263226, 0.8160498218131407,
0.17389442853722373, 0.7956044195067877],
[0, 12, 10, 17, -26]),
(np.double, [0.0, 0.031066908499895136, 0.5214135908877832,
0.45780736035689296, 0.5906586745934036],
[0, -801, 51, 194, -653]),
pytest.param(
np.longdouble,
[0.0, 0.20492557202724854, 0.4277180662199366, 0.9888085019891495,
0.9620175814461964],
[0, -7400, 14266, -7822, -8721],
marks=[
pytest.mark.skipif(
np.finfo(np.double) == np.finfo(np.longdouble),
reason="long double is same as double"),
pytest.mark.skipif(
platform.machine().startswith("ppc"),
reason="IBM double double"),
]
)
])
def test_roundtrip(self, ftype, frac_vals, exp_vals):
for frac, exp in zip(frac_vals, exp_vals):
f = np.ldexp(frac, exp, dtype=ftype)
n, d = f.as_integer_ratio()

try:
# workaround for gh-9968
nf = np.longdouble(str(n))
df = np.longdouble(str(d))
except (OverflowError, RuntimeWarning):
# the values may not fit in any float type
pytest.skip("longdouble too small on this platform")

assert_equal(nf / df, f, "{}/{}".format(n, d))