bpo-29882: Add an efficient popcount method for integers (#771)

* bpo-29882: Add an efficient popcount method for integers

* Update 'sign bit' and versionadded in docs

* Add entry to whatsnew document

* Doc: use positive example, mention population count

* Minor cleanups of the core code

* Move popcount_digit closer to where it's used

* Use z instead of self after conversion

* Add 'absolute value' and 'population count' to docstring

* Fix clinic error about missing summary line

* Ensure popcount_digit is portable with 64-bit ints

Co-authored-by: Mark Dickinson <dickinsm@gmail.com>

1 files changed, 26 insertions, 1 deletions

diff --git a/Objects/clinic/longobject.c.h b/Objects/clinic/longobject.c.h
index 7db8965..cf388c5 100644
--- a/Objects/clinic/longobject.c.h
+++ b/Objects/clinic/longobject.c.h
@@ -138,6 +138,31 @@ int_bit_length(PyObject *self, PyObject *Py_UNUSED(ignored))
     return int_bit_length_impl(self);
 }
 
+PyDoc_STRVAR(int_bit_count__doc__,
+"bit_count($self, /)\n"
+"--\n"
+"\n"
+"Number of ones in the binary representation of the absolute value of self.\n"
+"\n"
+"Also known as the population count.\n"
+"\n"
+">>> bin(13)\n"
+"\'0b1101\'\n"
+">>> (13).bit_count()\n"
+"3");
+
+#define INT_BIT_COUNT_METHODDEF    \
+    {"bit_count", (PyCFunction)int_bit_count, METH_NOARGS, int_bit_count__doc__},
+
+static PyObject *
+int_bit_count_impl(PyObject *self);
+
+static PyObject *
+int_bit_count(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    return int_bit_count_impl(self);
+}
+
 PyDoc_STRVAR(int_as_integer_ratio__doc__,
 "as_integer_ratio($self, /)\n"
 "--\n"
@@ -308,4 +333,4 @@ skip_optional_kwonly:
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=63b8274fc784d617 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=4257cfdb155efd00 input=a9049054013a1b77]*/