2 * Copyright (C) 2011 The Android Open Source Project
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
17 #ifndef ART_RUNTIME_LEB128_H_
18 #define ART_RUNTIME_LEB128_H_
22 #include "base/bit_utils.h"
23 #include "base/logging.h"
28 // Reads an unsigned LEB128 value, updating the given pointer to point
29 // just past the end of the read value. This function tolerates
30 // non-zero high-order bits in the fifth encoded byte.
31 static inline uint32_t DecodeUnsignedLeb128(const uint8_t** data) {
32 const uint8_t* ptr = *data;
33 int result = *(ptr++);
34 if (UNLIKELY(result > 0x7f)) {
36 result = (result & 0x7f) | ((cur & 0x7f) << 7);
39 result |= (cur & 0x7f) << 14;
42 result |= (cur & 0x7f) << 21;
44 // Note: We don't check to see if cur is out of range here,
45 // meaning we tolerate garbage in the four high-order bits.
53 return static_cast<uint32_t>(result);
56 static inline bool DecodeUnsignedLeb128Checked(const uint8_t** data,
59 const uint8_t* ptr = *data;
63 int result = *(ptr++);
64 if (UNLIKELY(result > 0x7f)) {
69 result = (result & 0x7f) | ((cur & 0x7f) << 7);
75 result |= (cur & 0x7f) << 14;
81 result |= (cur & 0x7f) << 21;
86 // Note: We don't check to see if cur is out of range here,
87 // meaning we tolerate garbage in the four high-order bits.
95 *out = static_cast<uint32_t>(result);
99 // Reads an unsigned LEB128 + 1 value. updating the given pointer to point
100 // just past the end of the read value. This function tolerates
101 // non-zero high-order bits in the fifth encoded byte.
102 // It is possible for this function to return -1.
103 static inline int32_t DecodeUnsignedLeb128P1(const uint8_t** data) {
104 return DecodeUnsignedLeb128(data) - 1;
107 // Reads a signed LEB128 value, updating the given pointer to point
108 // just past the end of the read value. This function tolerates
109 // non-zero high-order bits in the fifth encoded byte.
110 static inline int32_t DecodeSignedLeb128(const uint8_t** data) {
111 const uint8_t* ptr = *data;
112 int32_t result = *(ptr++);
113 if (result <= 0x7f) {
114 result = (result << 25) >> 25;
117 result = (result & 0x7f) | ((cur & 0x7f) << 7);
119 result = (result << 18) >> 18;
122 result |= (cur & 0x7f) << 14;
124 result = (result << 11) >> 11;
127 result |= (cur & 0x7f) << 21;
129 result = (result << 4) >> 4;
131 // Note: We don't check to see if cur is out of range here,
132 // meaning we tolerate garbage in the four high-order bits.
143 static inline bool DecodeSignedLeb128Checked(const uint8_t** data,
146 const uint8_t* ptr = *data;
150 int32_t result = *(ptr++);
151 if (result <= 0x7f) {
152 result = (result << 25) >> 25;
158 result = (result & 0x7f) | ((cur & 0x7f) << 7);
160 result = (result << 18) >> 18;
166 result |= (cur & 0x7f) << 14;
168 result = (result << 11) >> 11;
174 result |= (cur & 0x7f) << 21;
176 result = (result << 4) >> 4;
181 // Note: We don't check to see if cur is out of range here,
182 // meaning we tolerate garbage in the four high-order bits.
190 *out = static_cast<uint32_t>(result);
194 // Returns the number of bytes needed to encode the value in unsigned LEB128.
195 static inline uint32_t UnsignedLeb128Size(uint32_t data) {
196 // bits_to_encode = (data != 0) ? 32 - CLZ(x) : 1 // 32 - CLZ(data | 1)
197 // bytes = ceil(bits_to_encode / 7.0); // (6 + bits_to_encode) / 7
198 uint32_t x = 6 + 32 - CLZ(data | 1U);
199 // Division by 7 is done by (x * 37) >> 8 where 37 = ceil(256 / 7).
200 // This works for 0 <= x < 256 / (7 * 37 - 256), i.e. 0 <= x <= 85.
201 return (x * 37) >> 8;
204 // Returns the number of bytes needed to encode the value in unsigned LEB128.
205 static inline uint32_t SignedLeb128Size(int32_t data) {
206 // Like UnsignedLeb128Size(), but we need one bit beyond the highest bit that differs from sign.
207 data = data ^ (data >> 31);
208 uint32_t x = 1 /* we need to encode the sign bit */ + 6 + 32 - CLZ(data | 1U);
209 return (x * 37) >> 8;
212 static inline uint8_t* EncodeUnsignedLeb128(uint8_t* dest, uint32_t value) {
213 uint8_t out = value & 0x7f;
216 *dest++ = out | 0x80;
224 template <typename Vector>
225 static inline void EncodeUnsignedLeb128(Vector* dest, uint32_t value) {
226 static_assert(std::is_same<typename Vector::value_type, uint8_t>::value, "Invalid value type");
227 uint8_t out = value & 0x7f;
230 dest->push_back(out | 0x80);
234 dest->push_back(out);
237 // Overwrite encoded Leb128 with a new value. The new value must be less than
238 // or equal to the old value to ensure that it fits the allocated space.
239 static inline void UpdateUnsignedLeb128(uint8_t* dest, uint32_t value) {
240 const uint8_t* old_end = dest;
241 uint32_t old_value = DecodeUnsignedLeb128(&old_end);
242 DCHECK_LE(value, old_value);
243 for (uint8_t* end = EncodeUnsignedLeb128(dest, value); end < old_end; end++) {
244 // Use longer encoding than necessary to fill the allocated space.
250 static inline uint8_t* EncodeSignedLeb128(uint8_t* dest, int32_t value) {
251 uint32_t extra_bits = static_cast<uint32_t>(value ^ (value >> 31)) >> 6;
252 uint8_t out = value & 0x7f;
253 while (extra_bits != 0u) {
254 *dest++ = out | 0x80;
263 template<typename Vector>
264 static inline void EncodeSignedLeb128(Vector* dest, int32_t value) {
265 static_assert(std::is_same<typename Vector::value_type, uint8_t>::value, "Invalid value type");
266 uint32_t extra_bits = static_cast<uint32_t>(value ^ (value >> 31)) >> 6;
267 uint8_t out = value & 0x7f;
268 while (extra_bits != 0u) {
269 dest->push_back(out | 0x80);
274 dest->push_back(out);
277 // An encoder that pushes int32_t/uint32_t data onto the given std::vector.
278 template <typename Vector = std::vector<uint8_t>>
279 class Leb128Encoder {
280 static_assert(std::is_same<typename Vector::value_type, uint8_t>::value, "Invalid value type");
283 explicit Leb128Encoder(Vector* data) : data_(data) {
284 DCHECK(data != nullptr);
287 void Reserve(uint32_t size) {
288 data_->reserve(size);
291 void PushBackUnsigned(uint32_t value) {
292 EncodeUnsignedLeb128(data_, value);
295 template<typename It>
296 void InsertBackUnsigned(It cur, It end) {
297 for (; cur != end; ++cur) {
298 PushBackUnsigned(*cur);
302 void PushBackSigned(int32_t value) {
303 EncodeSignedLeb128(data_, value);
306 template<typename It>
307 void InsertBackSigned(It cur, It end) {
308 for (; cur != end; ++cur) {
309 PushBackSigned(*cur);
313 const Vector& GetData() const {
321 DISALLOW_COPY_AND_ASSIGN(Leb128Encoder);
324 // An encoder with an API similar to vector<uint32_t> where the data is captured in ULEB128 format.
325 template <typename Vector = std::vector<uint8_t>>
326 class Leb128EncodingVector FINAL : private Vector,
327 public Leb128Encoder<Vector> {
328 static_assert(std::is_same<typename Vector::value_type, uint8_t>::value, "Invalid value type");
331 Leb128EncodingVector() : Leb128Encoder<Vector>(this) { }
333 explicit Leb128EncodingVector(const typename Vector::allocator_type& alloc)
335 Leb128Encoder<Vector>(this) { }
338 DISALLOW_COPY_AND_ASSIGN(Leb128EncodingVector);
343 #endif // ART_RUNTIME_LEB128_H_