Skip to content

bpo-41902: Add fast path for long_div if the divisor is one #22480

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
corona10 wants to merge 2 commits into from
Closed

bpo-41902: Add fast path for long_div if the divisor is one #22480

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
66f902a
bpo-41902: Add fast path for long_div if the divisor is one
corona10 Oct 1, 2020
ceafada
bpo-41902: fix
corona10 Oct 1, 2020
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
5 changes: 4 additions & 1 deletion Lib/test/test_long.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -204,7 +204,10 @@ def test_division(self):
self.check_division(710031681576388032, 26769404391308)
self.check_division(1933622614268221, 30212853348836)


@support.cpython_only
def test_division_with_one(self):

@vstinner vstinner Oct 1, 2020

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

If you test assertIs(), please add a comment mentioning bpo-41902 and explain that it's a micro-optimization which returns x for x//1 if x is an int made of a single digit.

for n in range(10000000):

@vstinner vstinner Oct 1, 2020

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Well, I don't think that it's worth it to test 10000000 numbers. Just test a bunch of various numbers made of a single digit. Like:

(-MASK, -10, -5, 0, 1, 2, 42, MASK)

self.assertEqual(n, n // 1)

@vstinner vstinner Oct 1, 2020

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I suggest to test assertIs().


@vstinner vstinner Oct 1, 2020

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Test also that assertEqual(type(x//1), int) where x is an int subclass.

def test_karatsuba(self):
digits = list(range(1, 5)) + list(range(KARATSUBA_CUTOFF,
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-10-02-00-53-08.bpo-41902.owZSPO.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Add fast path for long_div if the divisor is one. Patch by Dong-hee Na.
4 changes: 4 additions & 0 deletions Objects/longobject.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -3695,6 +3695,10 @@ static PyObject *
long_div(PyObject *a, PyObject *b)
{
PyLongObject *div;
if (b == _PyLong_One && PyLong_CheckExact(a)) {

@pablogsal pablogsal Oct 1, 2020 •
edited
Loading

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This branch may impact the normal path, we certainly should benchmark this with PGO and cpu isolation.

Py_INCREF(a);
return a;
}

CHECK_BINOP(a, b);

Expand Down