1 /*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 /*
18 * Functions for interpreting LEB128 (little endian base 128) values
19 */
20
21 #ifndef LIBDEX_LEB128_H_
22 #define LIBDEX_LEB128_H_
23
24 #include "DexFile.h"
25
26 /*
27 * Reads an unsigned LEB128 value, updating the given pointer to point
28 * just past the end of the read value. This function tolerates
29 * non-zero high-order bits in the fifth encoded byte.
30 */
readUnsignedLeb128(const u1 ** pStream)31 DEX_INLINE int readUnsignedLeb128(const u1** pStream) {
32 const u1* ptr = *pStream;
33 int result = *(ptr++);
34
35 if (result > 0x7f) {
36 int cur = *(ptr++);
37 result = (result & 0x7f) | ((cur & 0x7f) << 7);
38 if (cur > 0x7f) {
39 cur = *(ptr++);
40 result |= (cur & 0x7f) << 14;
41 if (cur > 0x7f) {
42 cur = *(ptr++);
43 result |= (cur & 0x7f) << 21;
44 if (cur > 0x7f) {
45 /*
46 * Note: We don't check to see if cur is out of
47 * range here, meaning we tolerate garbage in the
48 * high four-order bits.
49 */
50 cur = *(ptr++);
51 result |= cur << 28;
52 }
53 }
54 }
55 }
56
57 *pStream = ptr;
58 return result;
59 }
60
61 /*
62 * Reads a signed LEB128 value, updating the given pointer to point
63 * just past the end of the read value. This function tolerates
64 * non-zero high-order bits in the fifth encoded byte.
65 */
readSignedLeb128(const u1 ** pStream)66 DEX_INLINE int readSignedLeb128(const u1** pStream) {
67 const u1* ptr = *pStream;
68 int result = *(ptr++);
69
70 if (result <= 0x7f) {
71 result = (result << 25) >> 25;
72 } else {
73 int cur = *(ptr++);
74 result = (result & 0x7f) | ((cur & 0x7f) << 7);
75 if (cur <= 0x7f) {
76 result = (result << 18) >> 18;
77 } else {
78 cur = *(ptr++);
79 result |= (cur & 0x7f) << 14;
80 if (cur <= 0x7f) {
81 result = (result << 11) >> 11;
82 } else {
83 cur = *(ptr++);
84 result |= (cur & 0x7f) << 21;
85 if (cur <= 0x7f) {
86 result = (result << 4) >> 4;
87 } else {
88 /*
89 * Note: We don't check to see if cur is out of
90 * range here, meaning we tolerate garbage in the
91 * high four-order bits.
92 */
93 cur = *(ptr++);
94 result |= cur << 28;
95 }
96 }
97 }
98 }
99
100 *pStream = ptr;
101 return result;
102 }
103
104 /*
105 * Reads an unsigned LEB128 value, updating the given pointer to point
106 * just past the end of the read value and also indicating whether the
107 * value was syntactically valid. The only syntactically *invalid*
108 * values are ones that are five bytes long where the final byte has
109 * any but the low-order four bits set. Additionally, if the limit is
110 * passed as non-NULL and bytes would need to be read past the limit,
111 * then the read is considered invalid.
112 */
113 int readAndVerifyUnsignedLeb128(const u1** pStream, const u1* limit,
114 bool* okay);
115
116 /*
117 * Reads a signed LEB128 value, updating the given pointer to point
118 * just past the end of the read value and also indicating whether the
119 * value was syntactically valid. The only syntactically *invalid*
120 * values are ones that are five bytes long where the final byte has
121 * any but the low-order four bits set. Additionally, if the limit is
122 * passed as non-NULL and bytes would need to be read past the limit,
123 * then the read is considered invalid.
124 */
125 int readAndVerifySignedLeb128(const u1** pStream, const u1* limit, bool* okay);
126
127
128 /*
129 * Writes a 32-bit value in unsigned ULEB128 format.
130 *
131 * Returns the updated pointer.
132 */
writeUnsignedLeb128(u1 * ptr,u4 data)133 DEX_INLINE u1* writeUnsignedLeb128(u1* ptr, u4 data)
134 {
135 while (true) {
136 u1 out = data & 0x7f;
137 if (out != data) {
138 *ptr++ = out | 0x80;
139 data >>= 7;
140 } else {
141 *ptr++ = out;
142 break;
143 }
144 }
145
146 return ptr;
147 }
148
149 /*
150 * Returns the number of bytes needed to encode "val" in ULEB128 form.
151 */
unsignedLeb128Size(u4 data)152 DEX_INLINE int unsignedLeb128Size(u4 data)
153 {
154 int count = 0;
155
156 do {
157 data >>= 7;
158 count++;
159 } while (data != 0);
160
161 return count;
162 }
163
164 #endif
165