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Moved Rational._binary_float_to_ratio() to float.as_integer_ratio() because

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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.
This commit is contained in:
Jeffrey Yasskin 2008-01-27 23:08:46 +00:00
parent 56eadd9d0d
commit 3ea7b41b58
3 changed files with 180 additions and 56 deletions
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159
Objects/floatobject.c
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@ -1161,6 +1161,163 @@ float_float(PyObject *v)
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 @@ static PyMethodDef float_methods[] = {
"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},