From 514d738d9eb21c611390fd415bf4e87f3a7a8696 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Fri, 22 May 2026 09:25:51 +0300
Subject: [PATCH] gh-85989: add HAVE_DOUBLE_ROUNDING check to test.support

---
 Lib/test/support/__init__.py | 6 ++++++
 Lib/test/test_builtin.py     | 7 +------
 Lib/test/test_math.py        | 7 +------
 Lib/test/test_statistics.py  | 8 +-------
 4 files changed, 9 insertions(+), 19 deletions(-)

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index 2cac70f4ab2afb..0348074ba6c8c6 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -73,6 +73,7 @@
     "run_no_yield_async_fn", "run_yielding_async_fn", "async_yield",
     "reset_code", "on_github_actions",
     "requires_root_user", "requires_non_root_user",
+    "HAVE_DOUBLE_ROUNDING",
     ]
 
 
@@ -524,6 +525,11 @@ def dec(*args, **kwargs):
     float.__getformat__("double").startswith("IEEE"),
     "test requires IEEE 754 doubles")
 
+# detect evidence of double-rounding: fsum is not always correctly
+# rounded on machines that suffer from double rounding.
+x, y = 1e16, 2.9999 # use temporary values to defeat peephole optimizer
+HAVE_DOUBLE_ROUNDING = (x + y == 1e16 + 4)
+
 def requires_zlib(reason='requires zlib'):
     try:
         import zlib
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 1f52b16948c703..a3566eb38b3063 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -39,7 +39,7 @@
 from test.support.script_helper import assert_python_ok
 from test.support.testcase import ComplexesAreIdenticalMixin
 from test.support.warnings_helper import check_warnings
-from test.support import requires_IEEE_754
+from test.support import HAVE_DOUBLE_ROUNDING, requires_IEEE_754
 from unittest.mock import MagicMock, patch
 try:
     import pty, signal
@@ -47,11 +47,6 @@
     pty = signal = None
 
 
-# Detect evidence of double-rounding: sum() does not always
-# get improved accuracy on machines that suffer from double rounding.
-x, y = 1e16, 2.9999 # use temporary values to defeat peephole optimizer
-HAVE_DOUBLE_ROUNDING = (x + y == 1e16 + 4)
-
 # used as proof of globals being used
 A_GLOBAL_VALUE = 123
 A_SENTINEL = sentinel("A_SENTINEL")
diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
index 8f9a239bead130..dd142aeb0cb888 100644
--- a/Lib/test/test_math.py
+++ b/Lib/test/test_math.py
@@ -1,7 +1,7 @@
 # Python test set -- math module
 # XXXX Should not do tests around zero only
 
-from test.support import verbose, requires_IEEE_754
+from test.support import HAVE_DOUBLE_ROUNDING, verbose, requires_IEEE_754
 from test import support
 import unittest
 import fractions
@@ -23,11 +23,6 @@
 FLOAT_MAX = sys.float_info.max
 FLOAT_MIN = sys.float_info.min
 
-# detect evidence of double-rounding: fsum is not always correctly
-# rounded on machines that suffer from double rounding.
-x, y = 1e16, 2.9999 # use temporary values to defeat peephole optimizer
-HAVE_DOUBLE_ROUNDING = (x + y == 1e16 + 4)
-
 # locate file with test values
 if __name__ == '__main__':
     file = sys.argv[0]
diff --git a/Lib/test/test_statistics.py b/Lib/test/test_statistics.py
index 677a87b51b9192..18ac5b17b9b481 100644
--- a/Lib/test/test_statistics.py
+++ b/Lib/test/test_statistics.py
@@ -16,7 +16,7 @@
 import sys
 import unittest
 from test import support
-from test.support import import_helper, requires_IEEE_754
+from test.support import HAVE_DOUBLE_ROUNDING, import_helper, requires_IEEE_754
 
 from decimal import Decimal
 from fractions import Fraction
@@ -28,12 +28,6 @@
 
 # === Helper functions and class ===
 
-# Test copied from Lib/test/test_math.py
-# detect evidence of double-rounding: fsum is not always correctly
-# rounded on machines that suffer from double rounding.
-x, y = 1e16, 2.9999 # use temporary values to defeat peephole optimizer
-HAVE_DOUBLE_ROUNDING = (x + y == 1e16 + 4)
-
 def sign(x):
     """Return -1.0 for negatives, including -0.0, otherwise +1.0."""
     return math.copysign(1, x)