EXEPACK2 - Revision history

Jsummers: /* Specifications */

2022-10-16T12:54:27Z

‎Specifications

Jsummers at 18:55, 1 June 2022

2022-06-01T18:55:49Z

Jsummers: Created page with "{{FormatInfo |formattype=electronic |subcat=Compression |released=1994 }} '''EXEPACK2''', or '''EXEPACK:2''', is the (informal?) name of a compressed data format used in some ..."

2022-05-26T18:45:48Z

Created page with "{{FormatInfo |formattype=electronic |subcat=Compression |released=1994 }} '''EXEPACK2''', or '''EXEPACK:2''', is the (informal?) name of a compressed data format used in some ..."

New page

{{FormatInfo
|formattype=electronic
|subcat=Compression
|released=1994
}}
'''EXEPACK2''', or '''EXEPACK:2''', is the (informal?) name of a compressed data format used in some OS/2 executable files, and certain other OS/2 formats. It was introduced in OS/2 Warp (OS/2 3.0).

Such executables are usually created by using the "/EXEPACK:2" option of the LINK386 utility, or by the special REPACK utility.

The decompressor is built into the OS/2 loader, so a compressed executable does not contain the code for decompressing itself.

== See also ==
* [[EXEPACK]]
* [[OS/2 Boot Logo]]

== Format details ==
The compression scheme is essentially a derivative of [[LZ77]]/[[LZSS]], with a 4K history buffer. It also incorporates [[run-length encoding]].

Assuming that [[OS/2 Boot Logo]] files use the same EXEPACK2 compression as executables, there is a significant error in the Wynn/Wu paper. For a "Long String token", it says the length field is biased by 3, when in fact it is not biased.

Other clarifications:
* When a token specifies both a set of uncompressed bytes, and a copy-from-history instruction, it is processed as if it were two separate instructions, in that order.
* The "distance back" values are encoded such that the most recently decompressed byte is 1, not 0 as it is in most formats.

== Specifications ==
* [https://cis.temple.edu/~wu/research/publications/Publications_2000.html 2000 Publications (Jie Wu)] → A. C. Wynn and J. Wu, "[https://cis.temple.edu/~wu/research/publications/Publication_files/The%20Effect%20of%20Compression%20on%20Performance%20in%20a%20Demand%20Paging%20System.pdf The Effect of Compression on Performance in a Demand Paging System]," Journal of Systems and Software, 30, 2000, 151-170 - §3.2. Exepack2 page-based compression.

== Software ==
* [https://www.os2site.com/sw/dev/misc/] → repack
* [https://github.com/bitwiseworks/lxlite lxLite] - possibly related
* See also [[OS/2 Boot Logo#Software]], notably lgoproc.

[[Category:Executable compression]]
[[Category:OS/2]]

@@ Line 24: / Line 24: @@
 == Specifications ==
-* [https://cis.temple.edu/~wu/research/publications/Publications_2000.html 2000 Publications (Jie Wu)] → A. C. Wynn and J. Wu, "[https://cis.temple.edu/~wu/research/publications/Publication_files/The%20Effect%20of%20Compression%20on%20Performance%20in%20a%20Demand%20Paging%20System.pdf The Effect of Compression on Performance in a Demand Paging System]," Journal of Systems and Software, 30, 2000, 151-170 - §3.2. Exepack2 page-based compression.
+* [https://cis.temple.edu/~wu/research/publications/Publications_2000.html 2000 Publications (Jie Wu)] → A. C. Wynn and J. Wu, "[https://cis.temple.edu/~wu/research/publications/Publication_files/The%20Effect%20of%20Compression%20on%20Performance%20in%20a%20Demand%20Paging%20System.pdf The Effect of Compression on Performance in a Demand Paging System]," Journal of Systems and Software 50 (2000), pp. 151-170 - §3.2. Exepack2 page-based compression.
 == Software ==

@@ Line 4: / Line 4: @@
 |released=1994
 }}
-'''EXEPACK2''', or '''EXEPACK:2''', is the (informal?) name of a compressed data format used in some OS/2 executable files, and certain other OS/2 formats. It was introduced in OS/2 Warp (OS/2 3.0).
+'''EXEPACK2''', or '''EXEPACK:2''', is the (informal?) name of a compressed data format used in some OS/2 executable files (see [[Linear Executable]]), and certain other OS/2 formats. It was introduced in OS/2 Warp (OS/2 3.0).
 Such executables are usually created by using the "/EXEPACK:2" option of the LINK386 utility, or by the special REPACK utility.
@@ Line 17: / Line 17: @@
 The compression scheme is essentially a derivative of [[LZ77]]/[[LZSS]], with a 4K history buffer. It also incorporates [[run-length encoding]].
-Assuming that [[OS/2 Boot Logo]] files use the same EXEPACK2 compression as executables, there is a significant error in the Wynn/Wu paper. For a "Long String token", it says the length field is biased by 3, when in fact it is not biased.
+Assuming that [[OS/2 Boot Logo]] files use the same EXEPACK2 compression as executables, there is a small but significant error in the Wynn/Wu paper. For a "Long String token", it says the length field is biased by 3, when in fact it is not biased.
 Other clarifications: