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29
30// memory_range.h: Define the google_breakpad::MemoryRange class, which
31// is a lightweight wrapper with a pointer and a length to encapsulate
32// a contiguous range of memory.
33
34#ifndef COMMON_MEMORY_RANGE_H_
35#define COMMON_MEMORY_RANGE_H_
36
37#include <stddef.h>
38
39#include "google_breakpad/common/breakpad_types.h"
40
41namespace google_breakpad {
42
43// A lightweight wrapper with a pointer and a length to encapsulate a
44// contiguous range of memory. It provides helper methods for checked
45// access of a subrange of the memory. Its implemementation does not
46// allocate memory or call into libc functions, and is thus safer to use
47// in a crashed environment.
48class MemoryRange {
49 public:
50 MemoryRange() : data_(NULL), length_(0) {}
51
52 MemoryRange(const void* data, size_t length) {
53 Set(data, length);
54 }
55
56 // Returns true if this memory range contains no data.
57 bool IsEmpty() const {
58 // Set() guarantees that |length_| is zero if |data_| is NULL.
59 return length_ == 0;
60 }
61
62 // Resets to an empty range.
63 void Reset() {
64 data_ = NULL;
65 length_ = 0;
66 }
67
68 // Sets this memory range to point to |data| and its length to |length|.
69 void Set(const void* data, size_t length) {
70 data_ = reinterpret_cast<const uint8_t*>(data);
71 // Always set |length_| to zero if |data_| is NULL.
72 length_ = data ? length : 0;
73 }
74
75 // Returns true if this range covers a subrange of |sub_length| bytes
76 // at |sub_offset| bytes of this memory range, or false otherwise.
77 bool Covers(size_t sub_offset, size_t sub_length) const {
78 // The following checks verify that:
79 // 1. sub_offset is within [ 0 .. length_ - 1 ]
80 // 2. sub_offset + sub_length is within
81 // [ sub_offset .. length_ ]
82 return sub_offset < length_ &&
83 sub_offset + sub_length >= sub_offset &&
84 sub_offset + sub_length <= length_;
85 }
86
87 // Returns a raw data pointer to a subrange of |sub_length| bytes at
88 // |sub_offset| bytes of this memory range, or NULL if the subrange
89 // is out of bounds.
90 const void* GetData(size_t sub_offset, size_t sub_length) const {
91 return Covers(sub_offset, sub_length) ? (data_ + sub_offset) : NULL;
92 }
93
94 // Same as the two-argument version of GetData() but uses sizeof(DataType)
95 // as the subrange length and returns an |DataType| pointer for convenience.
96 template <typename DataType>
97 const DataType* GetData(size_t sub_offset) const {
98 return reinterpret_cast<const DataType*>(
99 GetData(sub_offset, sizeof(DataType)));
100 }
101
102 // Returns a raw pointer to the |element_index|-th element of an array
103 // of elements of length |element_size| starting at |sub_offset| bytes
104 // of this memory range, or NULL if the element is out of bounds.
105 const void* GetArrayElement(size_t element_offset,
106 size_t element_size,
107 unsigned element_index) const {
108 size_t sub_offset = element_offset + element_index * element_size;
109 return GetData(sub_offset, element_size);
110 }
111
112 // Same as the three-argument version of GetArrayElement() but deduces
113 // the element size using sizeof(ElementType) and returns an |ElementType|
114 // pointer for convenience.
115 template <typename ElementType>
116 const ElementType* GetArrayElement(size_t element_offset,
117 unsigned element_index) const {
118 return reinterpret_cast<const ElementType*>(
119 GetArrayElement(element_offset, sizeof(ElementType), element_index));
120 }
121
122 // Returns a subrange of |sub_length| bytes at |sub_offset| bytes of
123 // this memory range, or an empty range if the subrange is out of bounds.
124 MemoryRange Subrange(size_t sub_offset, size_t sub_length) const {
125 return Covers(sub_offset, sub_length) ?
126 MemoryRange(data_ + sub_offset, sub_length) : MemoryRange();
127 }
128
129 // Returns a pointer to the beginning of this memory range.
130 const uint8_t* data() const { return data_; }
131
132 // Returns the length, in bytes, of this memory range.
133 size_t length() const { return length_; }
134
135 private:
136 // Pointer to the beginning of this memory range.
137 const uint8_t* data_;
138
139 // Length, in bytes, of this memory range.
140 size_t length_;
141};
142
143} // namespace google_breakpad
144
145#endif // COMMON_MEMORY_RANGE_H_
146