openvcdiff | 311c714 | 2008-08-26 19:29:25 +0000 | [diff] [blame] | 1 | // Copyright 2008 Google Inc. |
| 2 | // Author: Lincoln Smith |
| 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 | #ifndef OPEN_VCDIFF_DECODETABLE_H_ |
| 17 | #define OPEN_VCDIFF_DECODETABLE_H_ |
| 18 | |
| 19 | #include <config.h> |
openvcdiff | 28db807 | 2008-10-10 23:29:11 +0000 | [diff] [blame] | 20 | #include <stddef.h> // NULL |
openvcdiff | 311c714 | 2008-08-26 19:29:25 +0000 | [diff] [blame] | 21 | #include <stdint.h> // int32_t |
openvcdiff | 311c714 | 2008-08-26 19:29:25 +0000 | [diff] [blame] | 22 | #include <memory> // auto_ptr |
| 23 | #include "codetable.h" // VCDiffInstructi... |
| 24 | #include "logging.h" |
| 25 | |
| 26 | namespace open_vcdiff { |
| 27 | |
| 28 | // This class is used by the decoder. It can use a standard or |
| 29 | // non-standard code table, and will translate the opcodes in the code table |
| 30 | // into delta instructions. |
| 31 | // |
| 32 | // NOT threadsafe. |
| 33 | // |
| 34 | class VCDiffCodeTableReader { |
| 35 | public: |
| 36 | // When constructed, the object will be set up to use the default code table. |
| 37 | // If a non-default code table is to be used, then UseCodeTable() |
| 38 | // should be called after the VCDiffCodeTableReader has been constructed. |
| 39 | // In any case, the Init() method must be called before GetNextInstruction() |
| 40 | // may be used. |
| 41 | // |
| 42 | VCDiffCodeTableReader(); |
| 43 | |
| 44 | // Sets up a non-standard code table. The caller |
| 45 | // may free the memory occupied by the argument code table after |
| 46 | // passing it to this method, because the argument code table |
| 47 | // allocates space to store a copy of it. |
| 48 | // UseCodeTable() may be called either before or after calling Init(). |
| 49 | // Returns true if the code table was accepted, or false if the |
| 50 | // argument did not appear to be a valid code table. |
| 51 | // |
| 52 | bool UseCodeTable(const VCDiffCodeTableData& code_table_data, |
| 53 | unsigned char max_mode); |
| 54 | |
| 55 | // Defines the buffer containing the instructions and sizes. |
| 56 | // This method must be called before GetNextInstruction() may be used. |
| 57 | // Init() may be called any number of times to reset the state of |
| 58 | // the object. |
| 59 | // |
| 60 | void Init(const char** instructions_and_sizes, |
| 61 | const char* instructions_and_sizes_end) { |
| 62 | instructions_and_sizes_ = instructions_and_sizes; |
| 63 | instructions_and_sizes_end_ = instructions_and_sizes_end; |
| 64 | last_instruction_start_ = NULL; |
| 65 | pending_second_instruction_ = kNoOpcode; |
| 66 | last_pending_second_instruction_ = kNoOpcode; |
| 67 | } |
| 68 | |
| 69 | // Updates the pointers to the buffer containing the instructions and sizes, |
| 70 | // but leaves the rest of the reader state intact, so that (for example) |
| 71 | // any pending second instruction or unread instruction will still be |
| 72 | // read when requested. NOTE: UnGetInstruction() will not work immediately |
| 73 | // after using UpdatePointers(); GetNextInstruction() must be called first. |
| 74 | // |
| 75 | void UpdatePointers(const char** instructions_and_sizes, |
| 76 | const char* instructions_and_sizes_end) { |
| 77 | instructions_and_sizes_ = instructions_and_sizes; |
| 78 | instructions_and_sizes_end_ = instructions_and_sizes_end; |
| 79 | last_instruction_start_ = *instructions_and_sizes; |
| 80 | // pending_second_instruction_ is unchanged |
| 81 | last_pending_second_instruction_ = pending_second_instruction_; |
| 82 | } |
| 83 | |
| 84 | // Returns the next instruction from the stream of opcodes, |
| 85 | // or VCD_INSTRUCTION_END_OF_DATA if the end of the opcode stream is reached, |
| 86 | // or VCD_INSTRUCTION_ERROR if an error occurred. |
| 87 | // In the first of these cases, increments *instructions_and_sizes_ |
| 88 | // past the values it reads, and populates *size |
| 89 | // with the corresponding size for the returned instruction; |
| 90 | // otherwise, the value of *size is undefined, and is not |
| 91 | // guaranteed to be preserved. |
| 92 | // If the instruction returned is VCD_COPY, *mode will |
| 93 | // be populated with the copy mode; otherwise, the value of *mode |
| 94 | // is undefined, and is not guaranteed to be preserved. |
| 95 | // Any occurrences of VCD_NOOP in the opcode stream |
| 96 | // are skipped over and ignored, not returned. |
| 97 | // If Init() was not called before calling this method, then |
| 98 | // VCD_INSTRUCTION_ERROR will be returned. |
| 99 | // |
| 100 | VCDiffInstructionType GetNextInstruction(int32_t* size, unsigned char* mode); |
| 101 | |
| 102 | // Puts a single instruction back onto the front of the |
| 103 | // instruction stream. The next call to GetNextInstruction() |
| 104 | // will return the same value that was returned by the last |
| 105 | // call. Calling UnGetInstruction() more than once before calling |
| 106 | // GetNextInstruction() will have no additional effect; you can |
| 107 | // only rewind one instruction. |
| 108 | // |
| 109 | void UnGetInstruction() { |
| 110 | if (last_instruction_start_) { |
| 111 | if (last_instruction_start_ > *instructions_and_sizes_) { |
openvcdiff@gmail.com | 732fff2 | 2010-08-04 18:00:00 +0000 | [diff] [blame] | 112 | VCD_DFATAL << "Internal error: last_instruction_start past end of " |
| 113 | "instructions_and_sizes in UnGetInstruction" << VCD_ENDL; |
openvcdiff | 311c714 | 2008-08-26 19:29:25 +0000 | [diff] [blame] | 114 | } |
| 115 | *instructions_and_sizes_ = last_instruction_start_; |
| 116 | if ((pending_second_instruction_ != kNoOpcode) && |
| 117 | (last_pending_second_instruction_ != kNoOpcode)) { |
openvcdiff@gmail.com | 732fff2 | 2010-08-04 18:00:00 +0000 | [diff] [blame] | 118 | VCD_DFATAL << "Internal error: two pending instructions in a row " |
| 119 | "in UnGetInstruction" << VCD_ENDL; |
openvcdiff | 311c714 | 2008-08-26 19:29:25 +0000 | [diff] [blame] | 120 | } |
| 121 | pending_second_instruction_ = last_pending_second_instruction_; |
| 122 | } |
| 123 | } |
| 124 | |
| 125 | private: |
| 126 | // A pointer to the code table. This is the object that will be used |
| 127 | // to interpret opcodes in GetNextInstruction(). |
| 128 | const VCDiffCodeTableData* code_table_data_; |
| 129 | |
| 130 | // If the default code table is not being used, then space for the |
| 131 | // code table data will be allocated using this pointer and freed |
| 132 | // when the VCDiffCodeTableReader is destroyed. This will keep the |
| 133 | // code that uses the object from having to worry about memory |
| 134 | // management for the non-standard code table, whose contents have |
| 135 | // been read as part of the encoded data file/stream. |
| 136 | // |
| 137 | std::auto_ptr<VCDiffCodeTableData> non_default_code_table_data_; |
| 138 | |
| 139 | const char** instructions_and_sizes_; |
| 140 | const char* instructions_and_sizes_end_; |
| 141 | const char* last_instruction_start_; |
| 142 | OpcodeOrNone pending_second_instruction_; |
| 143 | OpcodeOrNone last_pending_second_instruction_; |
| 144 | |
| 145 | // Making these private avoids implicit copy constructor & assignment operator |
| 146 | VCDiffCodeTableReader(const VCDiffCodeTableReader&); |
| 147 | void operator=(const VCDiffCodeTableReader&); |
| 148 | }; |
| 149 | |
| 150 | }; // namespace open_vcdiff |
| 151 | |
| 152 | #endif // OPEN_VCDIFF_DECODETABLE_H_ |