Information technology -- Streaming Lossless Data Compression algorithm (SLDC)
ISO/IEC 22091:2002 specifies a lossless compression algorithm to reduce the number of 8-bit bytes required to represent data records and File Marks. The algorithm is known as Streaming Lossless Data Compression algorithm (SLDC). ISO/IEC 22091:2002 is based on ISO/IEC 15220. It extends that algorithm with the addition of control symbols that allow records of different sizes and compressibility, along with File Marks, to be efficiently encoded into an output stream which requires little or no additional control information for later decoding. The numerical identifier according to ISO/IEC 11576 allocated to this algorithm is 6.
Technologies de l'information -- Algorithme de compression sans perte de données en mode continu (SLDC)
Standards Content (sample)
Information technology — Streaming
Lossless Data Compression algorithm
Technologies de l’information — Algorithme de compression sans perte de
données en mode continu (SDLC)
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1 Scope 1
2 Conformance 1
3 Normative reference 1
4 Terms and definitions 1
4.1 Access Point 1
4.2 Control Symbol 1
4.3 Copy Pointer 1
4.4 data byte 1
4.5 Data Symbol 1
4.6 Displacement Field 1
4.7 Encoded Data Stream 1
4.8 Encoded Record 1
4.9 End Marker 2
4.10 End Of Record Symbol (EOR Symbol) 2
4.11 File Mark 2
4.12 File Mark Symbol 2
4.13 Flush Symbol 2
4.14 History Buffer 2
4.15 Literal 1 2
4.16 Literal 2 2
4.17 Matching String 2
4.18 Match Count 2
4.19 Match Count Field 2
4.20 Pad 2
4.21 Record 2
4.22 Record Segment 2
4.23 Reset X Symbol 2
4.24 Reset 1 Symbol 2
4.25 Reset 2 Symbol 2
4.26 scheme 1 2
4.27 Scheme 1 Symbol 2
4.28 scheme 2 3
4.29 Scheme 2 Symbol 3
4.30 user data 3
5 Conventions and Notations 3
5.1 Representation of numbers 3
5.2 Names 3
6 Acronyms 3
7 Algorithm Overview 3
7.1 Scheme 1 Encoding 3
7.2 Scheme 2 Encoding 3
7.3 History Buffer 4
8 Encoding Specification 4
8.1 User Data 4
8.2 History Buffer 4
8.3 Encoded Data Stream 4
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8.3.1 Access Point 5
8.4 Data Symbols 5
8.4.1 Literal 1 Data Symbols 5
8.4.2 Copy Pointer Data Symbols 5
8.4.3 Literal 2 Data Symbols 6
8.5 Control Symbols 7
8.6 Pad 8
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Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights.
ISO and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC 22091 was prepared by ECMA (as ECMA-321) and was adopted, under a special “fast-track procedure”, by Joint
Technical Committee ISO/IEC JTC 1, Information Technology, in parallel with its approval by national bodies of ISO and IEC.© ISO/IEC 2002 – All rights reserved v
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INTERNATIONAL STANDARD ISO/IEC 22091:2002(E)
Information technology — Streaming Lossless Data Compression algorithm (SLDC)
This International Standard specifies a lossless compression algorithm to reduce the number of 8-bit bytes required to represent
data records and File Marks. The algorithm is known as Streaming Lossless Data Compression algorithm (SLDC).One buffer size (1 024 bytes) is specified.
The numerical identifier according to ISO/IEC 11576 allocated to this algorithm is 6.2 Conformance
A compression algorithm shall be in conformance with this International Standard if its Encoded Data Stream satisfies therequirements of this International Standard.
3 Normative reference
The following normative document contains provisions which, through reference in this text, constitute provisions of this
International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply.
However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying
the most recent editions of the normative document indicated below. For undated references, the latest edition of the normative
document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards.
ISO/IEC 11576:1994 Information technology — Procedure for the registration of algorithms for the lossless compressionof data
4 Terms and definitions
For the purpose of this International Standard the following terms and definitions apply.4.1 Access Point
A location in the Encoded Data Stream at which data may be decoded.
4.2 Control Symbol
A Control Symbol may change the compression scheme, reset the History Buffer, mark the end of a Record, indicate a FileMark, or indicate the termination of an Encoded Data Stream.
4.3 Copy Pointer
A part of the Encoded Data Stream output in scheme 1 that replaces a string of data bytes with a specification of a MatchingString.
4.4 data byte
An element of user data that is to be encoded.
4.5 Data Symbol
An element of an Encoded Record that represents one or more data bytes.
4.6 Displacement Field
A field in the Copy Pointer that specifies the location within the History Buffer of the first byte of a Matching String.4.7 Encoded Data Stream
The output stream after encoding User Data.
4.8 Encoded Record
The output stream after encoding one Record of user data.
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4.9 End Marker
A Control Symbol that denotes termination of an Encoded Data Stream.
4.10 End Of Record Symbol (EOR Symbol)
A Control Symbol that denotes the end of a Record in the Encoded Data Stream.
4.11 File Mark
A recorded element used to mark organisational boundaries (e.g. directory boundaries) in user data.4.12 File Mark Symbol
A Control Symbol in Encoded Data Stream that denotes a File Mark in user data.
4.13 Flush Symbol
A Control Symbol that, if required, is followed by Pad to make the size of the Encoded Data Stream an integer multiple of32 bits.
4.14 History Buffer
A data structure where incoming data bytes are stored for use by scheme 1 compression and decompression.4.15 Literal 1
A part of the Encoded Data Stream, output in scheme 1, that represents a single data byte not encoded into any Copy Pointer.4.16 Literal 2
A part of the Encoded Data Stream, output in scheme 2, that represents a single data byte.4.17 Matching String
A sequence of two or more bytes in the History Buffer that is identical with a sequence of bytes in the user data.4.18 Match Count
The length, in bytes, of a Matching String.
4.19 Match Count Field
That part of a Copy Pointer that specifies the Match Count.
A number of bits inserted into the Encoded Data Stream so that the size of Encoded Data Stream is an integer multiple of32 bits.
An element of user data that contains at least one data byte.
4.22 Record Segment
A section of a Record encoded in a given scheme.
4.23 Reset X Symbol
A generic reference to either the Reset 1 Symbol or the Reset 2 Symbol.
4.24 Reset 1 Symbol
A Control Symbol that indicates History Buffer reset, and that subsequent symbols are encoded in scheme 1.4.25 Reset 2 Symbol
A Control Symbol that indicates History Buffer reset, and that subsequent symbols are encoded in scheme 2.4.26 scheme 1
A compression scheme that uses a History Buffer to achieve data compression.
4.27 Scheme 1 Symbol
A Control Symbol that indicates subsequent Data Symbols are either Copy Pointers or Literal 1s.© ISO/IEC 2002 – All rights reserved
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4.28 scheme 2
A packing scheme designed to encode uncompressible data with minimal expansion.
4.29 Scheme 2 Symbol
A Control Symbol that indicates subsequent Data Symbols are encoded in scheme 2.
4.30 user data
Information that is to be encoded, according to this compression algorithm.
5 Conventions and Notations
5.1 Representation of numbers
The following conventions and notations apply in this document unless otherwise stated.− The setting of bits is denoted by ZERO or ONE.
− Numbers in binary notation and bit combinations are strings of digits represented by ZEROs and ONEs with the mostsignificant bit to the left.
− Letters and digits in parentheses represent numbers in hexadecimal notation.
− All other numbers are in decimal form.
The names of basic elements, e.g. specific fields, are written with a capital initial letter.6 Acronyms
EOR End Of Record
lsb least significant bit
msb most significant bit
7 Algorithm Overview
User data that is to be compressed according to this International Standard consists of Records and File Marks. Records consistof 8-bit data bytes, and may be of any non-zero length.
Data bytes may be encoded in either scheme 1 or scheme 2.
7.1 Scheme 1 Encoding
There may exist within Records repeating strings of two or more data bytes such that information about the length and position
of one string may be substituted in place of a subsequent copy or copies of that same string. This information is known as a
Copy Pointer. This International Standard allows Copy Pointer substitution when corresponding bytes of the two strings are
offset by 1 to 1 023 data bytes within user data. Where string matches occur, data compression is possible, and the number of
bits of encoded data can be less than the number of bits of user data, and data compression is possible. Any data bytes that are
part of a repeated string may be encoded as a Copy Pointer. Any data byte that is not encoded as a Copy Pointer is encoded as a
Literal 1, in which a leading bit set to ZERO is added to the data byte, thereby indicating that this is a Literal 1. Regions over
which Copy Pointers and literal values are encoded are defined as being encoded according to scheme 1. Scheme 1 encoding is
identical with that of ISO/IEC 15200, except for the addition of Control Symbols....