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Commit 02cd6d7

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gh-130317: Fix strict aliasing in PyFloat_Pack8() (#133150)
* Fix strict aliasing in PyFloat_Pack8() and PyFloat_Pack4(). * Fix _testcapi.float_set_snan() on x86 (32-bit).
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‎Modules/_testcapi/float.c

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+5-2Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -182,8 +182,11 @@ _testcapi_float_set_snan(PyObject *module, PyObject *obj)
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uint64_t v;
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memcpy(&v, &d, 8);
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v &= ~(1ULL << 51); /* make sNaN */
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memcpy(&d, &v, 8);
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return PyFloat_FromDouble(d);
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// gh-130317: memcpy() is needed to preserve the sNaN flag on x86 (32-bit)
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PyObject *res = PyFloat_FromDouble(0.0);
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memcpy(&((PyFloatObject *)res)->ob_fval, &v, 8);
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return res;
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}
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static PyMethodDef test_methods[] = {

‎Objects/floatobject.c

Copy file name to clipboardExpand all lines: Objects/floatobject.c
+7-7Lines changed: 7 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -2197,12 +2197,10 @@ PyFloat_Pack4(double x, char *data, int le)
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memcpy(&v, &x, 8);
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if ((v & (1ULL << 51)) == 0) {
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union float_val {
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float f;
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uint32_t u32;
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} *py = (union float_val *)&y;
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py->u32 &= ~(1 << 22); /* make sNaN */
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uint32_t u32;
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memcpy(&u32, &y, 4);
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u32 &= ~(1 << 22); /* make sNaN */
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memcpy(&y, &u32, 4);
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}
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}
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@@ -2340,7 +2338,9 @@ PyFloat_Pack8(double x, char *data, int le)
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return -1;
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}
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else {
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const unsigned char *s = (unsigned char*)&x;
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unsigned char as_bytes[8];
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memcpy(as_bytes, &x, 8);
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const unsigned char *s = as_bytes;
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int i, incr = 1;
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if ((double_format == ieee_little_endian_format && !le)

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