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gh-130317: Fix strict aliasing in PyFloat_Pack8() (#133150)

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* Fix strict aliasing in PyFloat_Pack8() and PyFloat_Pack4().
* Fix _testcapi.float_set_snan() on x86 (32-bit).
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Victor Stinner 2025-04-29 16:27:50 +02:00 committed by GitHub
parent 698c6e3a0c
commit 02cd6d7097
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GPG Key ID: B5690EEEBB952194
2 changed files with 12 additions and 9 deletions
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7
Modules/_testcapi/float.c
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@ -182,8 +182,11 @@ _testcapi_float_set_snan(PyObject *module, PyObject *obj)
uint64_t v;
memcpy(&v, &d, 8);
v &= ~(1ULL << 51); /* make sNaN */
memcpy(&d, &v, 8);
return PyFloat_FromDouble(d);
// gh-130317: memcpy() is needed to preserve the sNaN flag on x86 (32-bit)
PyObject *res = PyFloat_FromDouble(0.0);
memcpy(&((PyFloatObject *)res)->ob_fval, &v, 8);
return res;
}
static PyMethodDef test_methods[] = {

14
Objects/floatobject.c
View File

@ -2197,12 +2197,10 @@ PyFloat_Pack4(double x, char *data, int le)
memcpy(&v, &x, 8);
if ((v & (1ULL << 51)) == 0) {
union float_val {
float f;
uint32_t u32;
} *py = (union float_val *)&y;
py->u32 &= ~(1 << 22); /* make sNaN */
uint32_t u32;
memcpy(&u32, &y, 4);
u32 &= ~(1 << 22); /* make sNaN */
memcpy(&y, &u32, 4);
}
}
@ -2340,7 +2338,9 @@ PyFloat_Pack8(double x, char *data, int le)
return -1;
}
else {
const unsigned char *s = (unsigned char*)&x;
unsigned char as_bytes[8];
memcpy(as_bytes, &x, 8);
const unsigned char *s = as_bytes;
int i, incr = 1;
if ((double_format == ieee_little_endian_format && !le)