text: // Copyright (C) 1994-2017 Free Software Foundation, Inc.
  //
  // This file is part of GCC.
  //
  // GCC is free software; you can redistribute it and/or modify
  // it under the terms of the GNU General Public License as published by
  // the Free Software Foundation; either version 3, or (at your option)
  // any later version.
  
  // GCC is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  // GNU General Public License for more details.
  
  // Under Section 7 of GPL version 3, you are granted additional
  // permissions described in the GCC Runtime Library Exception, version
  // 3.1, as published by the Free Software Foundation.
  
  // You should have received a copy of the GNU General Public License and
  // a copy of the GCC Runtime Library Exception along with this program;
  // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  // <http://www.gnu.org/licenses/>.
  
  #include "tinfo.h"
  
  namespace __cxxabiv1 {
  
  
  // this is the external interface to the dynamic cast machinery
  /* sub: source address to be adjusted; nonnull, and since the
   *      source object is polymorphic, *(void**)sub is a virtual pointer.
   * src: static type of the source object.
   * dst: destination type (the "T" in "dynamic_cast<T>(v)").
   * src2dst_offset: a static hint about the location of the
   *    source subobject with respect to the complete object;
   *    special negative values are:
   *       -1: no hint
   *       -2: src is not a public base of dst
   *       -3: src is a multiple public base type but never a
   *           virtual base type
   *    otherwise, the src type is a unique public nonvirtual
   *    base type of dst at offset src2dst_offset from the
   *    origin of dst.  */
  extern "C" void *
  __dynamic_cast (const void *src_ptr,    // object started from
                  const __class_type_info *src_type, // type of the starting object
                  const __class_type_info *dst_type, // desired target type
                  ptrdiff_t src2dst) // how src and dst are related
    {
    const void *vtable = *static_cast <const void *const *> (src_ptr);
    const vtable_prefix *prefix =
        adjust_pointer <vtable_prefix> (vtable, 
  				      -offsetof (vtable_prefix, origin));
    const void *whole_ptr =
        adjust_pointer <void> (src_ptr, prefix->whole_object);
    const __class_type_info *whole_type = prefix->whole_type;
    __class_type_info::__dyncast_result result;
  
    // If the whole object vptr doesn't refer to the whole object type, we're
    // in the middle of constructing a primary base, and src is a separate
    // base.  This has undefined behavior and we can't find anything outside
    // of the base we're actually constructing, so fail now rather than
    // segfault later trying to use a vbase offset that doesn't exist.
    const void *whole_vtable = *static_cast <const void *const *> (whole_ptr);
    const vtable_prefix *whole_prefix =
      adjust_pointer <vtable_prefix> (whole_vtable,
  				    -offsetof (vtable_prefix, origin));
    if (whole_prefix->whole_type != whole_type)
      return NULL;
    
    whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public,
                              dst_type, whole_ptr, src_type, src_ptr, result);
    if (!result.dst_ptr)
      return NULL;
    if (contained_public_p (result.dst2src))
      // Src is known to be a public base of dst.
      return const_cast <void *> (result.dst_ptr);
    if (contained_public_p (__class_type_info::__sub_kind (result.whole2src & result.whole2dst)))
      // Both src and dst are known to be public bases of whole. Found a valid
      // cross cast.
      return const_cast <void *> (result.dst_ptr);
    if (contained_nonvirtual_p (result.whole2src))
      // Src is known to be a non-public nonvirtual base of whole, and not a
      // base of dst. Found an invalid cross cast, which cannot also be a down
      // cast
      return NULL;
    if (result.dst2src == __class_type_info::__unknown)
      result.dst2src = dst_type->__find_public_src (src2dst, result.dst_ptr,
                                                    src_type, src_ptr);
    if (contained_public_p (result.dst2src))
      // Found a valid down cast
      return const_cast <void *> (result.dst_ptr);
    // Must be an invalid down cast, or the cross cast wasn't bettered
    return NULL;
  }
  
  }
  