+/* See value.h. */
+
+int
+value_union_variant (struct type *union_type, const gdb_byte *contents)
+{
+ gdb_assert (TYPE_CODE (union_type) == TYPE_CODE_UNION
+ && TYPE_FLAG_DISCRIMINATED_UNION (union_type));
+
+ struct dynamic_prop *discriminant_prop
+ = get_dyn_prop (DYN_PROP_DISCRIMINATED, union_type);
+ gdb_assert (discriminant_prop != nullptr);
+
+ struct discriminant_info *info
+ = (struct discriminant_info *) discriminant_prop->data.baton;
+ gdb_assert (info != nullptr);
+
+ /* If this is a univariant union, just return the sole field. */
+ if (TYPE_NFIELDS (union_type) == 1)
+ return 0;
+ /* This should only happen for univariants, which we already dealt
+ with. */
+ gdb_assert (info->discriminant_index != -1);
+
+ /* Compute the discriminant. Note that unpack_field_as_long handles
+ sign extension when necessary, as does the DWARF reader -- so
+ signed discriminants will be handled correctly despite the use of
+ an unsigned type here. */
+ ULONGEST discriminant = unpack_field_as_long (union_type, contents,
+ info->discriminant_index);
+
+ for (int i = 0; i < TYPE_NFIELDS (union_type); ++i)
+ {
+ if (i != info->default_index
+ && i != info->discriminant_index
+ && discriminant == info->discriminants[i])
+ return i;
+ }
+
+ if (info->default_index == -1)
+ error (_("Could not find variant corresponding to discriminant %s"),
+ pulongest (discriminant));
+ return info->default_index;
+}
+