/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_RUNTIME_LEB128_H_
#define ART_RUNTIME_LEB128_H_
#include <vector>
#include "base/bit_utils.h"
#include "base/logging.h"
#include "globals.h"
namespace art {
// Reads an unsigned LEB128 value, updating the given pointer to point
// just past the end of the read value. This function tolerates
// non-zero high-order bits in the fifth encoded byte.
static inline uint32_t DecodeUnsignedLeb128(const uint8_t** data) {
const uint8_t* ptr = *data;
int result = *(ptr++);
if (UNLIKELY(result > 0x7f)) {
int cur = *(ptr++);
result = (result & 0x7f) | ((cur & 0x7f) << 7);
if (cur > 0x7f) {
cur = *(ptr++);
result |= (cur & 0x7f) << 14;
if (cur > 0x7f) {
cur = *(ptr++);
result |= (cur & 0x7f) << 21;
if (cur > 0x7f) {
// Note: We don't check to see if cur is out of range here,
// meaning we tolerate garbage in the four high-order bits.
cur = *(ptr++);
result |= cur << 28;
}
}
}
}
*data = ptr;
return static_cast<uint32_t>(result);
}
// Reads an unsigned LEB128 + 1 value. updating the given pointer to point
// just past the end of the read value. This function tolerates
// non-zero high-order bits in the fifth encoded byte.
// It is possible for this function to return -1.
static inline int32_t DecodeUnsignedLeb128P1(const uint8_t** data) {
return DecodeUnsignedLeb128(data) - 1;
}
// Reads a signed LEB128 value, updating the given pointer to point
// just past the end of the read value. This function tolerates
// non-zero high-order bits in the fifth encoded byte.
static inline int32_t DecodeSignedLeb128(const uint8_t** data) {
const uint8_t* ptr = *data;
int32_t result = *(ptr++);
if (result <= 0x7f) {
result = (result << 25) >> 25;
} else {
int cur = *(ptr++);
result = (result & 0x7f) | ((cur & 0x7f) << 7);
if (cur <= 0x7f) {
result = (result << 18) >> 18;
} else {
cur = *(ptr++);
result |= (cur & 0x7f) << 14;
if (cur <= 0x7f) {
result = (result << 11) >> 11;
} else {
cur = *(ptr++);
result |= (cur & 0x7f) << 21;
if (cur <= 0x7f) {
result = (result << 4) >> 4;
} else {
// Note: We don't check to see if cur is out of range here,
// meaning we tolerate garbage in the four high-order bits.
cur = *(ptr++);
result |= cur << 28;
}
}
}
}
*data = ptr;
return result;
}
// Returns the number of bytes needed to encode the value in unsigned LEB128.
static inline uint32_t UnsignedLeb128Size(uint32_t data) {
// bits_to_encode = (data != 0) ? 32 - CLZ(x) : 1 // 32 - CLZ(data | 1)
// bytes = ceil(bits_to_encode / 7.0); // (6 + bits_to_encode) / 7
uint32_t x = 6 + 32 - CLZ(data | 1U);
// Division by 7 is done by (x * 37) >> 8 where 37 = ceil(256 / 7).
// This works for 0 <= x < 256 / (7 * 37 - 256), i.e. 0 <= x <= 85.
return (x * 37) >> 8;
}
// Returns the number of bytes needed to encode the value in unsigned LEB128.
static inline uint32_t SignedLeb128Size(int32_t data) {
// Like UnsignedLeb128Size(), but we need one bit beyond the highest bit that differs from sign.
data = data ^ (data >> 31);
uint32_t x = 1 /* we need to encode the sign bit */ + 6 + 32 - CLZ(data | 1U);
return (x * 37) >> 8;
}
static inline uint8_t* EncodeUnsignedLeb128(uint8_t* dest, uint32_t value) {
uint8_t out = value & 0x7f;
value >>= 7;
while (value != 0) {
*dest++ = out | 0x80;
out = value & 0x7f;
value >>= 7;
}
*dest++ = out;
return dest;
}
template <typename Vector>
static inline void EncodeUnsignedLeb128(Vector* dest, uint32_t value) {
static_assert(std::is_same<typename Vector::value_type, uint8_t>::value, "Invalid value type");
uint8_t out = value & 0x7f;
value >>= 7;
while (value != 0) {
dest->push_back(out | 0x80);
out = value & 0x7f;
value >>= 7;
}
dest->push_back(out);
}
// Overwrite encoded Leb128 with a new value. The new value must be less than
// or equal to the old value to ensure that it fits the allocated space.
static inline void UpdateUnsignedLeb128(uint8_t* dest, uint32_t value) {
const uint8_t* old_end = dest;
uint32_t old_value = DecodeUnsignedLeb128(&old_end);
DCHECK_LE(value, old_value);
for (uint8_t* end = EncodeUnsignedLeb128(dest, value); end < old_end; end++) {
// Use longer encoding than necessary to fill the allocated space.
end[-1] |= 0x80;
end[0] = 0;
}
}
static inline uint8_t* EncodeSignedLeb128(uint8_t* dest, int32_t value) {
uint32_t extra_bits = static_cast<uint32_t>(value ^ (value >> 31)) >> 6;
uint8_t out = value & 0x7f;
while (extra_bits != 0u) {
*dest++ = out | 0x80;
value >>= 7;
out = value & 0x7f;
extra_bits >>= 7;
}
*dest++ = out;
return dest;
}
template<typename Vector>
static inline void EncodeSignedLeb128(Vector* dest, int32_t value) {
static_assert(std::is_same<typename Vector::value_type, uint8_t>::value, "Invalid value type");
uint32_t extra_bits = static_cast<uint32_t>(value ^ (value >> 31)) >> 6;
uint8_t out = value & 0x7f;
while (extra_bits != 0u) {
dest->push_back(out | 0x80);
value >>= 7;
out = value & 0x7f;
extra_bits >>= 7;
}
dest->push_back(out);
}
// An encoder that pushes int32_t/uint32_t data onto the given std::vector.
template <typename Vector = std::vector<uint8_t>>
class Leb128Encoder {
static_assert(std::is_same<typename Vector::value_type, uint8_t>::value, "Invalid value type");
public:
explicit Leb128Encoder(Vector* data) : data_(data) {
DCHECK(data != nullptr);
}
void Reserve(uint32_t size) {
data_->reserve(size);
}
void PushBackUnsigned(uint32_t value) {
EncodeUnsignedLeb128(data_, value);
}
template<typename It>
void InsertBackUnsigned(It cur, It end) {
for (; cur != end; ++cur) {
PushBackUnsigned(*cur);
}
}
void PushBackSigned(int32_t value) {
EncodeSignedLeb128(data_, value);
}
template<typename It>
void InsertBackSigned(It cur, It end) {
for (; cur != end; ++cur) {
PushBackSigned(*cur);
}
}
const Vector& GetData() const {
return *data_;
}
protected:
Vector* const data_;
private:
DISALLOW_COPY_AND_ASSIGN(Leb128Encoder);
};
// An encoder with an API similar to vector<uint32_t> where the data is captured in ULEB128 format.
template <typename Vector = std::vector<uint8_t>>
class Leb128EncodingVector FINAL : private Vector,
public Leb128Encoder<Vector> {
static_assert(std::is_same<typename Vector::value_type, uint8_t>::value, "Invalid value type");
public:
Leb128EncodingVector() : Leb128Encoder<Vector>(this) { }
explicit Leb128EncodingVector(const typename Vector::allocator_type& alloc)
: Vector(alloc),
Leb128Encoder<Vector>(this) { }
private:
DISALLOW_COPY_AND_ASSIGN(Leb128EncodingVector);
};
} // namespace art
#endif // ART_RUNTIME_LEB128_H_