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GH-100425: Improve accuracy of builtin sum() for float inputs (GH-100426)

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Raymond Hettinger 2022-12-23 14:35:58 -08:00 • committed by GitHub
parent 1ecfd1ebf1
commit 5d84966cce
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6 changed files with 45 additions and 8 deletions
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18
Lib/test/test_builtin.py
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@ -9,6 +9,7 @@ import fractions
import gc
import io
import locale
import math
import os
import pickle
import platform
@ -31,6 +32,7 @@ from test.support import (swap_attr, maybe_get_event_loop_policy)
from test.support.os_helper import (EnvironmentVarGuard, TESTFN, unlink)
from test.support.script_helper import assert_python_ok
from test.support.warnings_helper import check_warnings
from test.support import requires_IEEE_754
from unittest.mock import MagicMock, patch
try:
import pty, signal
@ -38,6 +40,12 @@ except ImportError:
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)
class Squares:
def __init__(self, max):
@ -1617,6 +1625,8 @@ class BuiltinTest(unittest.TestCase):
self.assertEqual(repr(sum([-0.0])), '0.0')
self.assertEqual(repr(sum([-0.0], -0.0)), '-0.0')
self.assertEqual(repr(sum([], -0.0)), '-0.0')
self.assertTrue(math.isinf(sum([float("inf"), float("inf")])))
self.assertTrue(math.isinf(sum([1e308, 1e308])))
self.assertRaises(TypeError, sum)
self.assertRaises(TypeError, sum, 42)
@ -1641,6 +1651,14 @@ class BuiltinTest(unittest.TestCase):
sum(([x] for x in range(10)), empty)
self.assertEqual(empty, [])
@requires_IEEE_754
@unittest.skipIf(HAVE_DOUBLE_ROUNDING,
"sum accuracy not guaranteed on machines with double rounding")
@support.cpython_only # Other implementations may choose a different algorithm
def test_sum_accuracy(self):
self.assertEqual(sum([0.1] * 10), 1.0)
self.assertEqual(sum([1.0, 10E100, 1.0, -10E100]), 2.0)
def test_type(self):
self.assertEqual(type(''), type('123'))
self.assertNotEqual(type(''), type(()))