dynamic_cast.cc revision 227825
1#include "typeinfo.h" 2#include <stdio.h> 3 4using namespace ABI_NAMESPACE; 5 6/** 7 * Vtable header. 8 */ 9struct vtable_header 10{ 11 /** Offset of the leaf object. */ 12 ptrdiff_t leaf_offset; 13 /** Type of the object. */ 14 const __class_type_info *type; 15}; 16 17/** 18 * Simple macro that does pointer arithmetic in bytes but returns a value of 19 * the same type as the original. 20 */ 21#define ADD_TO_PTR(x, off) (__typeof__(x))(((char*)x) + off) 22 23bool __class_type_info::can_cast_to(const struct __class_type_info *other) const 24{ 25 return this == other; 26} 27 28void *__class_type_info::cast_to(void *obj, const struct __class_type_info *other) const 29{ 30 if (this == other) 31 { 32 return obj; 33 } 34 return 0; 35} 36 37 38bool __si_class_type_info::can_cast_to(const struct __class_type_info *other) const 39{ 40 return this == other || __base_type->can_cast_to(other); 41} 42 43void *__si_class_type_info::cast_to(void *obj, const struct __class_type_info *other) const 44{ 45 if (this == other) 46 { 47 return obj; 48 } 49 return __base_type->cast_to(obj, other); 50} 51 52 53bool __vmi_class_type_info::can_cast_to(const struct __class_type_info *other) const 54{ 55 if (this == other) 56 { 57 return true; 58 } 59 for (unsigned int i=0 ; i<__base_count ; i++) 60 { 61 const __base_class_type_info *info = &__base_info[i]; 62 if(info->isPublic() && info->__base_type->can_cast_to(other)) 63 { 64 return true; 65 } 66 } 67 return false; 68} 69 70void *__vmi_class_type_info::cast_to(void *obj, const struct __class_type_info *other) const 71{ 72 if (this == other) 73 { 74 return obj; 75 } 76 for (unsigned int i=0 ; i<__base_count ; i++) 77 { 78 const __base_class_type_info *info = &__base_info[i]; 79 ptrdiff_t offset = info->offset(); 80 // If this is a virtual superclass, the offset is stored in the 81 // object's vtable at the offset requested; 2.9.5.6.c: 82 // 83 // 'For a non-virtual base, this is the offset in the object of the 84 // base subobject. For a virtual base, this is the offset in the 85 // virtual table of the virtual base offset for the virtual base 86 // referenced (negative).' 87 88 if (info->isVirtual()) 89 { 90 // Object's vtable 91 ptrdiff_t *off = *(ptrdiff_t**)obj; 92 // Offset location in vtable 93 off = ADD_TO_PTR(off, offset); 94 offset = *off; 95 } 96 void *cast = ADD_TO_PTR(obj, offset); 97 98 if (info->__base_type == other) 99 { 100 return cast; 101 } 102 if ((cast = info->__base_type->cast_to(cast, other))) 103 { 104 return cast; 105 } 106 } 107 return 0; 108} 109 110/** 111 * ABI function used to implement the dynamic_cast<> operator. Some cases of 112 * this operator are implemented entirely in the compiler (e.g. to void*). 113 * This function implements the dynamic casts of the form dynamic_cast<T>(v). 114 * This will be translated to a call to this function with the value v as the 115 * first argument. The type id of the static type of v is the second argument 116 * and the type id of the destination type (T) is the third argument. 117 * 118 * The third argument is a hint about the compiler's guess at the correct 119 * pointer offset. If this value is negative, then -1 indicates no hint, -2 120 * that src is not a public base of dst, and -3 that src is a multiple public 121 * base type but never a virtual base type 122 */ 123extern "C" void* __dynamic_cast(const void *sub, 124 const __class_type_info *src, 125 const __class_type_info *dst, 126 ptrdiff_t src2dst_offset) 127{ 128 char *vtable_location = *(char**)sub; 129 const vtable_header *header = 130 (const vtable_header*)(vtable_location - sizeof(vtable_header)); 131 void *leaf = ADD_TO_PTR((void*)sub, header->leaf_offset); 132 return header->type->cast_to(leaf, dst); 133} 134