bpo-31373: fix undefined floating-point demotions (#3396)

1 files changed, 6 insertions, 4 deletions

diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 8c4fe74d1b..fc1ddf4081 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -2233,13 +2233,15 @@ _PyFloat_Pack4(double x, unsigned char *p, int le)
 
     }
     else {
-        float y = (float)x;
-        const unsigned char *s = (unsigned char*)&y;
         int i, incr = 1;
 
-        if (Py_IS_INFINITY(y) && !Py_IS_INFINITY(x))
+        if (fabs(x) > FLT_MAX && !Py_IS_INFINITY(x))
             goto Overflow;
 
+        unsigned char s[sizeof(float)];
+        float y = (float)x;
+        memcpy(s, &y, sizeof(float));
+
         if ((float_format == ieee_little_endian_format && !le)
             || (float_format == ieee_big_endian_format && le)) {
             p += 3;
@@ -2247,7 +2249,7 @@ _PyFloat_Pack4(double x, unsigned char *p, int le)
         }
 
         for (i = 0; i < 4; i++) {
-            *p = *s++;
+            *p = s[i];
             p += incr;
         }
         return 0;