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

1 files changed, 60 insertions, 2 deletions

diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 32e7cc8088..bbe8a19616 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -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 = {