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// Copyright 2008 The open-vcdiff Authors. All Rights Reserved.
// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// Classes to implement the Code Table
// described in sections 5.5, 5.6 and 7 of
// RFC 3284 - The VCDIFF Generic Differencing and Compression Data Format.
// The RFC text can be found at
#include <config.h>
#include <stdint.h> // uint16_t
namespace open_vcdiff {
// The instruction types from section 5.5 (mistakenly labeled 5.4) of the RFC.
enum VCDiffInstructionType {
VCD_ADD = 1,
VCD_RUN = 2,
// The following values are not true instruction types, but rather
// special condition values for functions that return VCDiffInstructionType.
const char* VCDiffInstructionName(VCDiffInstructionType inst);
// OpcodeOrNone: An opcode is a value between 0-255. There is not room
// in a single byte to express all these values plus a "no opcode found"
// value. So use a 16-bit integer to hold either an opcode or kNoOpcode.
typedef uint16_t OpcodeOrNone;
const OpcodeOrNone kNoOpcode = 0x100; // outside the opcode range 0x00 - 0xFF
// struct VCDiffCodeTableData:
// A representation of the VCDiff code table as six 256-byte arrays
// as described in Section 7 of RFC 3284. Each instruction code
// can represent up to two delta instructions, which is why inst,
// size, and mode each appear twice. Each of the two delta instructions
// has the following three attributes:
// * inst (NOOP, ADD, RUN, or COPY)
// * size (0-255 bytes) of the data to be copied; if this value is zero, then
// the size will be encoded separately from the instruction code, as a Varint
// * mode (SELF, HERE, NEAR(n), or SAME(n)), only used for COPY instructions
// Every valid code table should contain AT LEAST the following instructions:
// inst1=ADD size1=0 mode1=X inst2=NOOP size2=X mode2=X
// inst1=RUN size1=0 mode1=X inst2=NOOP size2=X mode2=X
// inst1=COPY size1=0 mode1=N inst2=NOOP size2=X mode2=X (for all N)
// ... where X represents a "don't care" value which will not be read,
// and N stands for every possible COPY mode between 0 and
// ([same cache size] + [here cache size]) inclusive.
// Without these instructions, it will be impossible to guarantee that
// all ADD, RUN, and COPY encoding requests can be fulfilled.
struct VCDiffCodeTableData {
static const int kCodeTableSize = 256;
static const VCDiffCodeTableData kDefaultCodeTableData;
// Validates that the data contained in the VCDiffCodeTableData structure
// does not violate certain assumptions. Returns true if none of these
// assumptions are violated, or false if an unexpected value is found.
// This function should be called on any non-default code table that is
// received as part of an encoded transmission.
// max_mode is the maximum value for the mode of a COPY instruction;
// this is equal to same_cache_size + near_cache_size + 1.
bool Validate(unsigned char max_mode) const;
// This version of Validate() assumes that the default address cache sizes
// are being used, and calculates max_mode based on that assumption.
bool Validate() const;
// The names of these elements are taken from RFC 3284 section 5.4
// (Instruction Codes), which contains the following specification:
// Each instruction code entry contains six fields, each of which is a single
// byte with an unsigned value:
// +-----------------------------------------------+
// | inst1 | size1 | mode1 | inst2 | size2 | mode2 |
// +-----------------------------------------------+
unsigned char inst1[kCodeTableSize]; // from enum VCDiffInstructionType
unsigned char inst2[kCodeTableSize]; // from enum VCDiffInstructionType
unsigned char size1[kCodeTableSize];
unsigned char size2[kCodeTableSize];
unsigned char mode1[kCodeTableSize]; // from enum VCDiffModes
unsigned char mode2[kCodeTableSize]; // from enum VCDiffModes
// Single-letter abbreviations that make it easier to read
// the default code table data.
static const VCDiffInstructionType N = VCD_NOOP;
static const VCDiffInstructionType A = VCD_ADD;
static const VCDiffInstructionType R = VCD_RUN;
static const VCDiffInstructionType C = VCD_COPY;
static bool ValidateOpcode(int opcode,
unsigned char inst,
unsigned char size,
unsigned char mode,
unsigned char max_mode,
const char* first_or_second);
} // namespace open_vcdiff