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Issue 3008: hex/oct/bin can show floats exactly.

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This commit is contained in:
Raymond Hettinger 2008-06-21 06:39:53 +00:00
parent db53c1eb68
commit e0e711446b
3 changed files with 90 additions and 2 deletions
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62
Objects/floatobject.c
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@ -1204,6 +1204,62 @@ PyDoc_STRVAR(float_as_integer_ratio_doc,
">>> (-.25).as_integer_ratio()\n"
"(-1, 4)");
static PyObject *
_float_to_base(PyFloatObject *v, unaryfunc int_to_base)
{
PyObject *mant, *conv, *result;
double x, fr;
int i, exp, n;
char *conv_str;
CONVERT_TO_DOUBLE(((PyObject *)v), x);
if (!Py_IS_FINITE(x))
return PyObject_Repr((PyObject *)v);
fr = frexp(x, &exp);
for (i=0; i<300 && fr != floor(fr) ; i++) {
fr *= 2.0;
exp--;
}
mant = PyLong_FromDouble(floor(fr));
if (mant == NULL)
return NULL;
conv = int_to_base(mant);
Py_DECREF(mant);
if (conv== NULL)
return NULL;
n = PyString_GET_SIZE(conv);
conv_str = PyString_AS_STRING(conv);
/* Remove the trailing 'L' if present */
if (n && conv_str[n-1] == 'L') {
PyObject *newconv = PySequence_GetSlice(conv, 0, -1);
Py_DECREF(conv);
if (newconv == NULL)
return NULL;
conv = newconv;
conv_str = PyString_AS_STRING(conv);
}
result = PyString_FromFormat("%s * 2.0 ** %d", conv_str, exp);
Py_DECREF(conv);
return result;
}
static PyObject *
float_hex(PyFloatObject *v)
{
return _float_to_base(v, PyLong_Type.tp_as_number->nb_hex);
}
static PyObject *
float_oct(PyFloatObject *v)
{
return _float_to_base(v, PyLong_Type.tp_as_number->nb_oct);
}
static PyObject *
float_bin(PyFloatObject *v)
{
return _float_to_base(v, PyLong_Type.tp_as_number->nb_bin);
}
static PyObject *
float_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds);
@ -1490,8 +1546,8 @@ static PyNumberMethods float_as_number = {
float_trunc, /*nb_int*/
float_trunc, /*nb_long*/
float_float, /*nb_float*/
0, /* nb_oct */
0, /* nb_hex */
(unaryfunc)float_oct, /* nb_oct */
(unaryfunc)float_hex, /* nb_hex */
0, /* nb_inplace_add */
0, /* nb_inplace_subtract */
0, /* nb_inplace_multiply */
@ -1507,6 +1563,8 @@ static PyNumberMethods float_as_number = {
float_div, /* nb_true_divide */
0, /* nb_inplace_floor_divide */
0, /* nb_inplace_true_divide */
0, /* nb_index */
(unaryfunc)float_bin, /* nb_bin */
};
PyTypeObject PyFloat_Type = {