libstdc++-v3/libsupc++/dyncast.cc

   1 // Copyright (C) 1994, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2007, 2009
   2 // Free Software Foundation
   3 //
   4 // This file is part of GCC.
   5 //
   6 // GCC is free software; you can redistribute it and/or modify
   7 // it under the terms of the GNU General Public License as published by
   8 // the Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // GCC is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 #include "tinfo.h"
  26
  27 namespace __cxxabiv1 {
  28
  29
  30 // this is the external interface to the dynamic cast machinery
  31 extern "C" void *
  32 __dynamic_cast (const void *src_ptr,    // object started from
  33                 const __class_type_info *src_type, // type of the starting object
  34                 const __class_type_info *dst_type, // desired target type
  35                 ptrdiff_t src2dst) // how src and dst are related
  36 {
  37   const void *vtable = *static_cast <const void *const *> (src_ptr);
  38   const vtable_prefix *prefix =
  39       adjust_pointer <vtable_prefix> (vtable,
  40                                       -offsetof (vtable_prefix, origin));
  41   const void *whole_ptr =
  42       adjust_pointer <void> (src_ptr, prefix->whole_object);
  43   const __class_type_info *whole_type = prefix->whole_type;
  44   __class_type_info::__dyncast_result result;
  45
  46   whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public,
  47                             dst_type, whole_ptr, src_type, src_ptr, result);
  48   if (!result.dst_ptr)
  49     return NULL;
  50   if (contained_public_p (result.dst2src))
  51     // Src is known to be a public base of dst.
  52     return const_cast <void *> (result.dst_ptr);
  53   if (contained_public_p (__class_type_info::__sub_kind (result.whole2src & result.whole2dst)))
  54     // Both src and dst are known to be public bases of whole. Found a valid
  55     // cross cast.
  56     return const_cast <void *> (result.dst_ptr);
  57   if (contained_nonvirtual_p (result.whole2src))
  58     // Src is known to be a non-public nonvirtual base of whole, and not a
  59     // base of dst. Found an invalid cross cast, which cannot also be a down
  60     // cast
  61     return NULL;
  62   if (result.dst2src == __class_type_info::__unknown)
  63     result.dst2src = dst_type->__find_public_src (src2dst, result.dst_ptr,
  64                                                   src_type, src_ptr);
  65   if (contained_public_p (result.dst2src))
  66     // Found a valid down cast
  67     return const_cast <void *> (result.dst_ptr);
  68   // Must be an invalid down cast, or the cross cast wasn't bettered
  69   return NULL;
  70 }
  71
  72 }