The previous code is correct, but hard to verify: The libmpdec documentation

Stefan Krah · Stefan Krah · commit 140893cbaa08 · 2012-04-18T17:48:34.000+02:00
rightfully states that an mpd_t with a coefficient flagged as MPD_CONST_DATA
must not be in the position of the result operand. In this particular case
several assumptions guarantee that a resize will never occur in all possible
code paths, which was the reason for using MPD_CONST_DATA and saving an
instruction by omitting the initialization of tmp.alloc.

For readability, tmp is now flagged as MPD_STATIC_DATA and tmp.alloc
is initialized.
diff --git a/Modules/_decimal/libmpdec/mpdecimal.c b/Modules/_decimal/libmpdec/mpdecimal.c
@@ -1280,7 +1280,8 @@ _mpd_qget_uint(int use_sign, const mpd_t *a, uint32_t *status)
         /* At this point a->digits+a->exp <= MPD_RDIGITS+1,
          * so the shift fits. */
         tmp.data = tmp_data;
-        tmp.flags = MPD_STATIC|MPD_CONST_DATA;
+        tmp.flags = MPD_STATIC|MPD_STATIC_DATA;
+        tmp.alloc = 2;
         mpd_qsshiftr(&tmp, a, -a->exp);
         tmp.exp = 0;
         a = &tmp;
