Issue #3439: add bit_length method to int and long.
Thanks Fredrik Johansson and Victor Stinner for code,
Raymond Hettinger for review.
diff --git a/Objects/intobject.c b/Objects/intobject.c
index e73c921..9baee8e 100644
--- a/Objects/intobject.c
+++ b/Objects/intobject.c
@@ -1138,6 +1138,40 @@
return NULL;
}
+static const unsigned char BitLengthTable[32] = {
+ 0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
+ 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5
+};
+
+static PyObject *
+int_bit_length(PyIntObject *v)
+{
+ unsigned long n;
+ long r = 0;
+
+ if (v->ob_ival < 0)
+ /* avoid undefined behaviour when v->ob_ival == -LONG_MAX-1 */
+ n = 0U-(unsigned long)v->ob_ival;
+ else
+ n = (unsigned long)v->ob_ival;
+
+ while (n >= 32) {
+ r += 6;
+ n >>= 6;
+ }
+ r += (long)(BitLengthTable[n]);
+ return PyInt_FromLong(r);
+}
+
+PyDoc_STRVAR(int_bit_length_doc,
+"int.bit_length() -> int\n\
+\n\
+Number of bits necessary to represent self in binary.\n\
+>>> bin(37)\n\
+'0b100101'\n\
+>>> (37).bit_length()\n\
+6");
+
#if 0
static PyObject *
int_is_finite(PyObject *v)
@@ -1149,6 +1183,8 @@
static PyMethodDef int_methods[] = {
{"conjugate", (PyCFunction)int_int, METH_NOARGS,
"Returns self, the complex conjugate of any int."},
+ {"bit_length", (PyCFunction)int_bit_length, METH_NOARGS,
+ int_bit_length_doc},
#if 0
{"is_finite", (PyCFunction)int_is_finite, METH_NOARGS,
"Returns always True."},