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// Copyright 2008 Google Inc.
// Author: Lincoln Smith
//
// 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.
//
// Types and value definitions to support the implementation of RFC 3284 -
// The VCDIFF Generic Differencing and Compression Data Format.
// The RFC text can be found at http://www.faqs.org/rfcs/rfc3284.html
// Many of the definitions below reference sections in that text.
#ifndef OPEN_VCDIFF_VCDIFF_DEFS_H_
#define OPEN_VCDIFF_VCDIFF_DEFS_H_
#include <config.h>
#include <limits.h> // UCHAR_MAX
#include <stdint.h> // int32_t
namespace open_vcdiff {
enum VCDiffResult {
RESULT_SUCCESS = 0,
// Many functions within open-vcdiff return signed integer types,
// and can also return either of these special negative values:
//
// An error occurred while performing the requested operation.
RESULT_ERROR = -1,
// The end of available data was reached
// before the requested operation could be completed.
RESULT_END_OF_DATA = -2
};
// The delta file header section as described in section 4.1 of the RFC:
//
// "Each delta file starts with a header section organized as below.
// Note the convention that square-brackets enclose optional items.
//
// Header1 - byte = 0xD6
// Header2 - byte = 0xC3
// Header3 - byte = 0xC4
// Header4 - byte
// Hdr_Indicator - byte
// [Secondary compressor ID] - byte
// [Length of code table data] - integer
// [Code table data]
//
// The first three Header bytes are the ASCII characters 'V', 'C' and
// 'D' with their most significant bits turned on (in hexadecimal, the
// values are 0xD6, 0xC3, and 0xC4). The fourth Header byte is
// currently set to zero. In the future, it might be used to indicate
// the version of Vcdiff."
//
typedef struct DeltaFileHeader {
unsigned char header1; // Always 0xD6 ('V' | 0x80)
unsigned char header2; // Always 0xC3 ('C' | 0x80)
unsigned char header3; // Always 0xC4 ('D' | 0x80)
unsigned char header4; // 0x00 for standard format, 'S' if extensions used
unsigned char hdr_indicator;
} DeltaFileHeader;
// The possible values for the Hdr_Indicator field, as described
// in section 4.1 of the RFC:
//
// "The Hdr_Indicator byte shows if there is any initialization data
// required to aid in the reconstruction of data in the Window sections.
// This byte MAY have non-zero values for either, both, or neither of
// the two bits VCD_DECOMPRESS and VCD_CODETABLE below:
//
// 7 6 5 4 3 2 1 0
// +-+-+-+-+-+-+-+-+
// | | | | | | | | |
// +-+-+-+-+-+-+-+-+
// ^ ^
// | |
// | +-- VCD_DECOMPRESS
// +---- VCD_CODETABLE
//
// If bit 0 (VCD_DECOMPRESS) is non-zero, this indicates that a
// secondary compressor may have been used to further compress certain
// parts of the delta encoding data [...]"
// [Secondary compressors are not supported by open-vcdiff.]
//
// "If bit 1 (VCD_CODETABLE) is non-zero, this indicates that an
// application-defined code table is to be used for decoding the delta
// instructions. [...]"
//
const unsigned char VCD_DECOMPRESS = 0x01;
const unsigned char VCD_CODETABLE = 0x02;
// The possible values for the Win_Indicator field, as described
// in section 4.2 of the RFC:
//
// "Win_Indicator:
//
// This byte is a set of bits, as shown:
//
// 7 6 5 4 3 2 1 0
// +-+-+-+-+-+-+-+-+
// | | | | | | | | |
// +-+-+-+-+-+-+-+-+
// ^ ^
// | |
// | +-- VCD_SOURCE
// +---- VCD_TARGET
//
// If bit 0 (VCD_SOURCE) is non-zero, this indicates that a
// segment of data from the "source" file was used as the
// corresponding source window of data to encode the target
// window. The decoder will use this same source data segment to
// decode the target window.
//
// If bit 1 (VCD_TARGET) is non-zero, this indicates that a
// segment of data from the "target" file was used as the
// corresponding source window of data to encode the target
// window. As above, this same source data segment is used to
// decode the target window.
//
// The Win_Indicator byte MUST NOT have more than one of the bits
// set (non-zero). It MAY have none of these bits set."
//
const unsigned char VCD_SOURCE = 0x01;
const unsigned char VCD_TARGET = 0x02;
// If this flag is set, the delta window includes an Adler32 checksum
// of the target window data. Not part of the RFC draft standard.
const unsigned char VCD_CHECKSUM = 0x04;
// The possible values for the Delta_Indicator field, as described
// in section 4.3 of the RFC:
//
// "Delta_Indicator:
// This byte is a set of bits, as shown:
//
// 7 6 5 4 3 2 1 0
// +-+-+-+-+-+-+-+-+
// | | | | | | | | |
// +-+-+-+-+-+-+-+-+
// ^ ^ ^
// | | |
// | | +-- VCD_DATACOMP
// | +---- VCD_INSTCOMP
// +------ VCD_ADDRCOMP
//
// VCD_DATACOMP: bit value 1.
// VCD_INSTCOMP: bit value 2.
// VCD_ADDRCOMP: bit value 4.
//
// [...] If the bit VCD_DECOMPRESS (Section 4.1) was on, each of these
// sections may have been compressed using the specified secondary
// compressor. The bit positions 0 (VCD_DATACOMP), 1
// (VCD_INSTCOMP), and 2 (VCD_ADDRCOMP) respectively indicate, if
// non-zero, that the corresponding parts are compressed."
// [Secondary compressors are not supported, so open-vcdiff decoding will fail
// if these bits are not all zero.]
//
const unsigned char VCD_DATACOMP = 0x01;
const unsigned char VCD_INSTCOMP = 0x02;
const unsigned char VCD_ADDRCOMP = 0x04;
// A COPY address has 32 bits, which places a limit
// of 2GB on the maximum combined size of the dictionary plus
// the target window (= the chunk of data to be encoded.)
typedef int32_t VCDAddress;
// The address modes used for COPY instructions, as defined in
// section 5.3 of the RFC.
//
// The first two modes (0 and 1) are defined as SELF (addressing forward
// from the beginning of the source window) and HERE (addressing backward
// from the current position in the source window + previously decoded
// target data.)
//
// After those first two modes, there are a variable number of NEAR modes
// (which take a recently-used address and add a positive offset to it)
// and SAME modes (which match a previously-used address using a "hash" of
// the lowest bits of the address.) The number of NEAR and SAME modes
// depends on the defined size of the address cache; since this number is
// variable, these modes cannot be specified as enum values.
enum VCDiffModes {
VCD_SELF_MODE = 0,
VCD_HERE_MODE = 1,
VCD_FIRST_NEAR_MODE = 2,
VCD_MAX_MODES = UCHAR_MAX + 1 // 256
};
} // namespace open_vcdiff
#endif // OPEN_VCDIFF_VCDIFF_DEFS_H_
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