https://github.com/python/cpython/commit/e9c11b749576dfb0eb2b1a40ae84f532f1526df5 commit: e9c11b749576dfb0eb2b1a40ae84f532f1526df5 branch: 3.14 author: Miss Islington (bot) <[email protected]> committer: vstinner <[email protected]> date: 2025-11-12T10:33:34Z summary:
[3.14] gh-141042: fix sNaN's packing for mixed floating-point formats (GH-141107) (#141459) gh-141042: fix sNaN's packing for mixed floating-point formats (GH-141107) (cherry picked from commit 23d85a2a3fb029172ea15c6e596f64f8c2868ed3) Co-authored-by: Sergey B Kirpichev <[email protected]> files: A Misc/NEWS.d/next/C_API/2025-11-06-06-28-14.gh-issue-141042.brOioJ.rst M Lib/test/test_capi/test_float.py M Objects/floatobject.c diff --git a/Lib/test/test_capi/test_float.py b/Lib/test/test_capi/test_float.py index 983b991b4f163d..df7017e6436a69 100644 --- a/Lib/test/test_capi/test_float.py +++ b/Lib/test/test_capi/test_float.py @@ -29,6 +29,23 @@ NAN = float("nan") +def make_nan(size, sign, quiet, payload=None): + if size == 8: + payload_mask = 0x7ffffffffffff + i = (sign << 63) + (0x7ff << 52) + (quiet << 51) + elif size == 4: + payload_mask = 0x3fffff + i = (sign << 31) + (0xff << 23) + (quiet << 22) + elif size == 2: + payload_mask = 0x1ff + i = (sign << 15) + (0x1f << 10) + (quiet << 9) + else: + raise ValueError("size must be either 2, 4, or 8") + if payload is None: + payload = random.randint(not quiet, payload_mask) + return i + payload + + class CAPIFloatTest(unittest.TestCase): def test_check(self): # Test PyFloat_Check() @@ -202,16 +219,7 @@ def test_pack_unpack_roundtrip_for_nans(self): # HP PA RISC uses 0 for quiet, see: # https://en.wikipedia.org/wiki/NaN#Encoding signaling = 1 - quiet = int(not signaling) - if size == 8: - payload = random.randint(signaling, 0x7ffffffffffff) - i = (sign << 63) + (0x7ff << 52) + (quiet << 51) + payload - elif size == 4: - payload = random.randint(signaling, 0x3fffff) - i = (sign << 31) + (0xff << 23) + (quiet << 22) + payload - elif size == 2: - payload = random.randint(signaling, 0x1ff) - i = (sign << 15) + (0x1f << 10) + (quiet << 9) + payload + i = make_nan(size, sign, not signaling) data = bytes.fromhex(f'{i:x}') for endian in (BIG_ENDIAN, LITTLE_ENDIAN): with self.subTest(data=data, size=size, endian=endian): @@ -221,6 +229,32 @@ def test_pack_unpack_roundtrip_for_nans(self): self.assertTrue(math.isnan(value)) self.assertEqual(data1, data2) + @unittest.skipUnless(HAVE_IEEE_754, "requires IEEE 754") + @unittest.skipUnless(sys.maxsize != 2147483647, "requires 64-bit mode") + def test_pack_unpack_nans_for_different_formats(self): + pack = _testcapi.float_pack + unpack = _testcapi.float_unpack + + for endian in (BIG_ENDIAN, LITTLE_ENDIAN): + with self.subTest(endian=endian): + byteorder = "big" if endian == BIG_ENDIAN else "little" + + # Convert sNaN to qNaN, if payload got truncated + data = make_nan(8, 0, False, 0x80001).to_bytes(8, byteorder) + snan_low = unpack(data, endian) + qnan4 = make_nan(4, 0, True, 0).to_bytes(4, byteorder) + qnan2 = make_nan(2, 0, True, 0).to_bytes(2, byteorder) + self.assertEqual(pack(4, snan_low, endian), qnan4) + self.assertEqual(pack(2, snan_low, endian), qnan2) + + # Preserve NaN type, if payload not truncated + data = make_nan(8, 0, False, 0x80000000001).to_bytes(8, byteorder) + snan_high = unpack(data, endian) + snan4 = make_nan(4, 0, False, 16384).to_bytes(4, byteorder) + snan2 = make_nan(2, 0, False, 2).to_bytes(2, byteorder) + self.assertEqual(pack(4, snan_high, endian), snan4) + self.assertEqual(pack(2, snan_high, endian), snan2) + if __name__ == "__main__": unittest.main() diff --git a/Misc/NEWS.d/next/C_API/2025-11-06-06-28-14.gh-issue-141042.brOioJ.rst b/Misc/NEWS.d/next/C_API/2025-11-06-06-28-14.gh-issue-141042.brOioJ.rst new file mode 100644 index 00000000000000..22a1aa1f405318 --- /dev/null +++ b/Misc/NEWS.d/next/C_API/2025-11-06-06-28-14.gh-issue-141042.brOioJ.rst @@ -0,0 +1,3 @@ +Make qNaN in :c:func:`PyFloat_Pack2` and :c:func:`PyFloat_Pack4`, if while +conversion to a narrower precision floating-point format --- the remaining +after truncation payload will be zero. Patch by Sergey B Kirpichev. diff --git a/Objects/floatobject.c b/Objects/floatobject.c index 93e1973d6b32fc..700b8d4cbeb9fd 100644 --- a/Objects/floatobject.c +++ b/Objects/floatobject.c @@ -2028,6 +2028,10 @@ PyFloat_Pack2(double x, char *data, int le) memcpy(&v, &x, sizeof(v)); v &= 0xffc0000000000ULL; bits = (unsigned short)(v >> 42); /* NaN's type & payload */ + /* set qNaN if no payload */ + if (!bits) { + bits |= (1<<9); + } } else { sign = (x < 0.0); @@ -2200,16 +2204,16 @@ PyFloat_Pack4(double x, char *data, int le) if ((v & (1ULL << 51)) == 0) { uint32_t u32; memcpy(&u32, &y, 4); - u32 &= ~(1 << 22); /* make sNaN */ + /* if have payload, make sNaN */ + if (u32 & 0x3fffff) { + u32 &= ~(1 << 22); + } memcpy(&y, &u32, 4); } #else uint32_t u32; memcpy(&u32, &y, 4); - if ((v & (1ULL << 51)) == 0) { - u32 &= ~(1 << 22); - } /* Workaround RISC-V: "If a NaN value is converted to a * different floating-point type, the result is the * canonical NaN of the new type". The canonical NaN here @@ -2220,6 +2224,10 @@ PyFloat_Pack4(double x, char *data, int le) /* add payload */ u32 -= (u32 & 0x3fffff); u32 += (uint32_t)((v & 0x7ffffffffffffULL) >> 29); + /* if have payload, make sNaN */ + if ((v & (1ULL << 51)) == 0 && (u32 & 0x3fffff)) { + u32 &= ~(1 << 22); + } memcpy(&y, &u32, 4); #endif _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
