gh-111495: Add tests for PyFloat C API

[skirpichev]

• Issue: Add more C API tests #111495

[skirpichev]

Some C API tests for floats are in Lib/test/test_float.py historically. An example:

cpython/Lib/test/test_float.py

Lines 1518 to 1569 in ed587be

	@unittest.skipIf(_testcapiisNone, 'needs _testcapi')
	classPackTests(unittest.TestCase):
	deftest_pack(self):
	self.assertEqual(_testcapi.float_pack(2, 1.5, BIG_ENDIAN),
	b'>\x00')
	self.assertEqual(_testcapi.float_pack(4, 1.5, BIG_ENDIAN),
	b'?\xc0\x00\x00')
	self.assertEqual(_testcapi.float_pack(8, 1.5, BIG_ENDIAN),
	b'?\xf8\x00\x00\x00\x00\x00\x00')
	self.assertEqual(_testcapi.float_pack(2, 1.5, LITTLE_ENDIAN),
	b'\x00>')
	self.assertEqual(_testcapi.float_pack(4, 1.5, LITTLE_ENDIAN),
	b'\x00\x00\xc0?')
	self.assertEqual(_testcapi.float_pack(8, 1.5, LITTLE_ENDIAN),
	b'\x00\x00\x00\x00\x00\x00\xf8?')
	deftest_unpack(self):
	self.assertEqual(_testcapi.float_unpack(b'>\x00', BIG_ENDIAN),
	1.5)
	self.assertEqual(_testcapi.float_unpack(b'?\xc0\x00\x00', BIG_ENDIAN),
	1.5)
	self.assertEqual(_testcapi.float_unpack(b'?\xf8\x00\x00\x00\x00\x00\x00', BIG_ENDIAN),
	1.5)
	self.assertEqual(_testcapi.float_unpack(b'\x00>', LITTLE_ENDIAN),
	1.5)
	self.assertEqual(_testcapi.float_unpack(b'\x00\x00\xc0?', LITTLE_ENDIAN),
	1.5)
	self.assertEqual(_testcapi.float_unpack(b'\x00\x00\x00\x00\x00\x00\xf8?', LITTLE_ENDIAN),
	1.5)
	deftest_roundtrip(self):
	large=2.0**100
	values= [1.0, 1.5, large, 1.0/7, math.pi]
	ifHAVE_IEEE_754:
	values.extend((INF, NAN))
	forvalueinvalues:
	forsizein (2, 4, 8,):
	ifsize==2andvalue==large:
	# too large for 16-bit float
	continue
	rel_tol=EPSILON[size]
	forendianin (BIG_ENDIAN, LITTLE_ENDIAN):
	withself.subTest(value=value, size=size, endian=endian):
	data=_testcapi.float_pack(size, value, endian)
	value2=_testcapi.float_unpack(data, endian)
	ifisnan(value):
	self.assertTrue(isnan(value2), (value, value2))
	elifsize<8:
	self.assertTrue(math.isclose(value2, value, rel_tol=rel_tol),
	(value, value2))
	else:
	self.assertEqual(value2, value)

In this PR this left intact, but maybe we should move them.

[sobolevn]

Just one suggestion :)
All other things LGTM.

[skirpichev]

Converted to a draft per review #111591

[serhiy-storchaka]

LGTM.

Thank you @skirpichev for your contribution and for your fast response.

[miss-islington-app]

Thanks @skirpichev for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[bedevere-app]

GH-111752 is a backport of this pull request to the 3.12 branch.

[skirpichev]

@serhiy-storchaka, thank you for review.