runtime/leb128.h - platform/art - Gitiles

 /*
  * 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 Allocator>
 static inline void EncodeUnsignedLeb128(std::vector<uint8_t, Allocator>* dest, uint32_t value) {
   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 Allocator>
 static inline void EncodeSignedLeb128(std::vector<uint8_t, Allocator>* 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->push_back(out | 0x80);
     value >>= 7;
     out = value & 0x7f;
     extra_bits >>= 7;
   }
   dest->push_back(out);
 }

 // An encoder that pushed uint32_t data onto the given std::vector.
 class Leb128Encoder {
  public:
   explicit Leb128Encoder(std::vector<uint8_t>* 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 std::vector<uint8_t>& GetData() const {
     return *data_;
   }

  protected:
   std::vector<uint8_t>* 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.
 class Leb128EncodingVector FINAL : private std::vector<uint8_t>, public Leb128Encoder {
  public:
   Leb128EncodingVector() : Leb128Encoder(this) {
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(Leb128EncodingVector);
 };

 }  // namespace art

 #endif  // ART_RUNTIME_LEB128_H_
	/*
	* 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 Allocator>
	static inline void EncodeUnsignedLeb128(std::vector<uint8_t, Allocator>* dest, uint32_t value) {
	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 Allocator>
	static inline void EncodeSignedLeb128(std::vector<uint8_t, Allocator>* 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->push_back(out \| 0x80);
	value >>= 7;
	out = value & 0x7f;
	extra_bits >>= 7;
	}
	dest->push_back(out);
	}

	// An encoder that pushed uint32_t data onto the given std::vector.
	class Leb128Encoder {
	public:
	explicit Leb128Encoder(std::vector<uint8_t>* 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 std::vector<uint8_t>& GetData() const {
	return *data_;
	}

	protected:
	std::vector<uint8_t>* 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.
	class Leb128EncodingVector FINAL : private std::vector<uint8_t>, public Leb128Encoder {
	public:
	Leb128EncodingVector() : Leb128Encoder(this) {
	}

	private:
	DISALLOW_COPY_AND_ASSIGN(Leb128EncodingVector);
	};

	} // namespace art

	#endif // ART_RUNTIME_LEB128_H_