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 | // 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_ |