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 // Classes to implement the Code Table 17 // described in sections 5.5, 5.6 and 7 of 18 // RFC 3284 - The VCDIFF Generic Differencing and Compression Data Format. 19 // The RFC text can be found at http://www.faqs.org/rfcs/rfc3284.html 20 21 #ifndef OPEN_VCDIFF_CODETABLE_H_ 22 #define OPEN_VCDIFF_CODETABLE_H_ 23 24 #include <config.h> 25 #include <stdint.h> // uint16_t 26 27 namespace open_vcdiff { 28 29 // The instruction types from section 5.5 (mistakenly labeled 5.4) of the RFC. 30 // 31 enum VCDiffInstructionType { 32 VCD_NOOP = 0, 33 VCD_ADD = 1, 34 VCD_RUN = 2, 35 VCD_COPY = 3, 36 VCD_LAST_INSTRUCTION_TYPE = VCD_COPY, 37 // The following values are not true instruction types, but rather 38 // special condition values for functions that return VCDiffInstructionType. 39 VCD_INSTRUCTION_ERROR = 4, 40 VCD_INSTRUCTION_END_OF_DATA = 5 41 }; 42 43 const char* VCDiffInstructionName(VCDiffInstructionType inst); 44 45 // OpcodeOrNone: An opcode is a value between 0-255. There is not room 46 // in a single byte to express all these values plus a "no opcode found" 47 // value. So use a 16-bit integer to hold either an opcode or kNoOpcode. 48 // 49 typedef uint16_t OpcodeOrNone; 50 const OpcodeOrNone kNoOpcode = 0x100; // outside the opcode range 0x00 - 0xFF 51 52 // struct VCDiffCodeTableData: 53 // 54 // A representation of the VCDiff code table as six 256-byte arrays 55 // as described in Section 7 of RFC 3284. Each instruction code 56 // can represent up to two delta instructions, which is why inst, 57 // size, and mode each appear twice. Each of the two delta instructions 58 // has the following three attributes: 59 // * inst (NOOP, ADD, RUN, or COPY) 60 // * size (0-255 bytes) of the data to be copied; if this value is zero, then 61 // the size will be encoded separately from the instruction code, as a Varint 62 // * mode (SELF, HERE, NEAR(n), or SAME(n)), only used for COPY instructions 63 // 64 // Every valid code table should contain AT LEAST the following instructions: 65 // inst1=ADD size1=0 mode1=X inst2=NOOP size2=X mode2=X 66 // inst1=RUN size1=0 mode1=X inst2=NOOP size2=X mode2=X 67 // inst1=COPY size1=0 mode1=N inst2=NOOP size2=X mode2=X (for all N) 68 // ... where X represents a "don't care" value which will not be read, 69 // and N stands for every possible COPY mode between 0 and 70 // ([same cache size] + [here cache size]) inclusive. 71 // Without these instructions, it will be impossible to guarantee that 72 // all ADD, RUN, and COPY encoding requests can be fulfilled. 73 // 74 struct VCDiffCodeTableData { 75 static const int kCodeTableSize = 256; 76 77 static const VCDiffCodeTableData kDefaultCodeTableData; 78 79 // Validates that the data contained in the VCDiffCodeTableData structure 80 // does not violate certain assumptions. Returns true if none of these 81 // assumptions are violated, or false if an unexpected value is found. 82 // This function should be called on any non-default code table that is 83 // received as part of an encoded transmission. 84 // max_mode is the maximum value for the mode of a COPY instruction; 85 // this is equal to same_cache_size + near_cache_size + 1. 86 // 87 bool Validate(unsigned char max_mode) const; 88 89 // This version of Validate() assumes that the default address cache sizes 90 // are being used, and calculates max_mode based on that assumption. 91 bool Validate() const; 92 93 // The names of these elements are taken from RFC 3284 section 5.4 94 // (Instruction Codes), which contains the following specification: 95 // 96 // Each instruction code entry contains six fields, each of which is a single 97 // byte with an unsigned value: 98 // +-----------------------------------------------+ 99 // | inst1 | size1 | mode1 | inst2 | size2 | mode2 | 100 // +-----------------------------------------------+ 101 // 102 unsigned char inst1[kCodeTableSize]; // from enum VCDiffInstructionType 103 unsigned char inst2[kCodeTableSize]; // from enum VCDiffInstructionType 104 unsigned char size1[kCodeTableSize]; 105 unsigned char size2[kCodeTableSize]; 106 unsigned char mode1[kCodeTableSize]; // from enum VCDiffModes 107 unsigned char mode2[kCodeTableSize]; // from enum VCDiffModes 108 109 private: 110 // Single-letter abbreviations that make it easier to read 111 // the default code table data. 112 static const VCDiffInstructionType N = VCD_NOOP; 113 static const VCDiffInstructionType A = VCD_ADD; 114 static const VCDiffInstructionType R = VCD_RUN; 115 static const VCDiffInstructionType C = VCD_COPY; 116 117 static bool ValidateOpcode(int opcode, 118 unsigned char inst, 119 unsigned char size, 120 unsigned char mode, 121 unsigned char max_mode, 122 const char* first_or_second); 123 }; 124 125 } // namespace open_vcdiff 126 127 #endif // OPEN_VCDIFF_CODETABLE_H_ 128
