Replace blocklist with allowlist

Author: vstinner

Objects/memoryobject.c

@@ -3101,25 +3101,6 @@ cmp_rec(const char *p, const char *q,
     return 1;
 }
 
-static int
-is_float_format(const char *format)
-{
-    if (format == NULL) {
-        return 0;
-    }
-    if (strcmp("d", format) == 0) {
-        return 1;
-    }
-    if (strcmp("f", format) == 0) {
-        return 1;
-    }
-    if (strcmp("e", format) == 0) {
-        return 1;
-    }
-    return 0;
-}
-
-
 static PyObject *
 memory_richcompare(PyObject *v, PyObject *w, int op)
 {
@@ -3143,10 +3124,24 @@ memory_richcompare(PyObject *v, PyObject *w, int op)
 
     // A memoryview is equal to itself: there is no need to compare individual
     // values. This is not true for float values since they can be NaN, and NaN
-    // is not equal to itself.
-    if (v == w && !is_float_format(vv->format)) {
-        equal = 1;
-        goto result;
+    // is not equal to itself. So only use this optimization on format known to
+    // not use floats.
+    if (v == w) {
+        int can_compare_ptrs;
+        const char *format = vv->format;
+        if (format != NULL) {
+            // Exclude formats "d" (double), "f" (float), "e" (16-bit float)
+            // and "P" (void*)
+            can_compare_ptrs = (strchr("bBchHiIlLnNqQ?", format[0]) != NULL
+                                && format[1] == 0);
+        }
+        else {
+            can_compare_ptrs = 1;
+        }
+        if (can_compare_ptrs) {
+            equal = 1;
+            goto result;
+        }
     }
 
     if (PyMemoryView_Check(w)) {