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gh-145633: Fix struct.pack('f') on s390x #146422

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gh-145633: Fix struct.pack('f') on s390x #146422

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eba13d8
gh-145633: Fix struct.pack('f') on s390x
vstinner Mar 25, 2026
ce1093b
Rewrite test_705836()
vstinner Mar 26, 2026
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15 changes: 15 additions & 0 deletions Lib/test/test_struct.py
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Original file line number Diff line number Diff line change
Expand Up @@ -397,6 +397,21 @@ def test_705836(self):
big = (1 << 25) - 1
big = math.ldexp(big, 127 - 24)
self.assertRaises(OverflowError, struct.pack, ">f", big)
self.assertRaises(OverflowError, struct.pack, "<f", big)
# same for native format, see gh-145633
self.assertRaises(OverflowError, struct.pack, "f", big)

# And for half-floats
big = (1 << 11) - 1
big = math.ldexp(big, 15 - 10)
packed = struct.pack(">e", big)
unpacked = struct.unpack(">e", packed)[0]
self.assertEqual(big, unpacked)
big = (1 << 12) - 1
big = math.ldexp(big, 15 - 11)
self.assertRaises(OverflowError, struct.pack, ">e", big)
self.assertRaises(OverflowError, struct.pack, "<e", big)
self.assertRaises(OverflowError, struct.pack, "e", big)

def test_1530559(self):
for code, byteorder in iter_integer_formats():
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5 changes: 2 additions & 3 deletions Modules/_struct.c
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Original file line number Diff line number Diff line change
Expand Up @@ -763,14 +763,13 @@ np_halffloat(_structmodulestate *state, char *p, PyObject *v, const formatdef *f
static int
np_float(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
{
float x = (float)PyFloat_AsDouble(v);
double x = PyFloat_AsDouble(v);
if (x == -1 && PyErr_Occurred()) {
PyErr_SetString(state->StructError,
"required argument is not a float");
return -1;
}
memcpy(p, &x, sizeof x);
return 0;
return PyFloat_Pack4(x, p, PY_LITTLE_ENDIAN);
}

static int
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