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

   1 // Copyright (C) 1994, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2007
   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 2, 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 // You should have received a copy of the GNU General Public License
  17 // along with GCC; see the file COPYING.  If not, write to
  18 // the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  19 // Boston, MA 02110-1301, USA.
  20
  21 // As a special exception, you may use this file as part of a free software
  22 // library without restriction.  Specifically, if other files instantiate
  23 // templates or use macros or inline enums from this file, or you compile
  24 // this file and link it with other files to produce an executable, this
  25 // file does not by itself cause the resulting executable to be covered by
  26 // the GNU General Public License.  This exception does not however
  27 // invalidate any other reasons why the executable file might be covered by
  28 // the GNU General Public License.
  29
  30 #include "tinfo.h"
  31
  32 namespace __cxxabiv1 {
  33
  34
  35 // this is the external interface to the dynamic cast machinery
  36 extern "C" void *
  37 __dynamic_cast (const void *src_ptr,    // object started from
  38                 const __class_type_info *src_type, // type of the starting object
  39                 const __class_type_info *dst_type, // desired target type
  40                 ptrdiff_t src2dst) // how src and dst are related
  41 {
  42   const void *vtable = *static_cast <const void *const *> (src_ptr);
  43   const vtable_prefix *prefix =
  44       adjust_pointer <vtable_prefix> (vtable,
  45                                       -offsetof (vtable_prefix, origin));
  46   const void *whole_ptr =
  47       adjust_pointer <void> (src_ptr, prefix->whole_object);
  48   const __class_type_info *whole_type = prefix->whole_type;
  49   __class_type_info::__dyncast_result result;
  50
  51   whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public,
  52                             dst_type, whole_ptr, src_type, src_ptr, result);
  53   if (!result.dst_ptr)
  54     return NULL;
  55   if (contained_public_p (result.dst2src))
  56     // Src is known to be a public base of dst.
  57     return const_cast <void *> (result.dst_ptr);
  58   if (contained_public_p (__class_type_info::__sub_kind (result.whole2src & result.whole2dst)))
  59     // Both src and dst are known to be public bases of whole. Found a valid
  60     // cross cast.
  61     return const_cast <void *> (result.dst_ptr);
  62   if (contained_nonvirtual_p (result.whole2src))
  63     // Src is known to be a non-public nonvirtual base of whole, and not a
  64     // base of dst. Found an invalid cross cast, which cannot also be a down
  65     // cast
  66     return NULL;
  67   if (result.dst2src == __class_type_info::__unknown)
  68     result.dst2src = dst_type->__find_public_src (src2dst, result.dst_ptr,
  69                                                   src_type, src_ptr);
  70   if (contained_public_p (result.dst2src))
  71     // Found a valid down cast
  72     return const_cast <void *> (result.dst_ptr);
  73   // Must be an invalid down cast, or the cross cast wasn't bettered
  74   return NULL;
  75 }
  76
  77 }