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Compression And Dynamic Decompression of Executable Code

IP.com Disclosure Number: IPCOM000101258D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Cheema, GS: AUTHOR [+3]

Abstract

Executable code can be loaded into memory in a compression format and dynamically decompressed to reduce the storage requirements of executable code. The process compresses an overlay library file such that each separate overlay can still be extracted from the file, when needed, without having to decompress the entire overlay library file. A modification to the compression algorithm keeps track of the buffer size that will be needed to decompress any character.

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Compression And Dynamic Decompression of Executable Code

       Executable code can be loaded into memory in a compression
format and dynamically decompressed to reduce the storage
requirements of executable code.  The process compresses an overlay
library file such that each separate overlay can still be extracted
from the file, when needed, without having to decompress the entire
overlay library file.  A modification to the compression algorithm
keeps track of the buffer size that will be needed to decompress any
character.

      As shown in the figure, there are six major functions in the
process.  The functions are: reader 10, overlay table reader 12,
overlay splitter 14, compression 16, overlay consolidation 18, and
overlay table writer 20.  The reader function 10 reads through the
address file 22 to identify the address information for the overlay
table 24 contained in the execute file 26.  The overlay table reader
function 12 uses the address information from the table location 28
to locate the overlay table in the execute file 26.  The process then
reads through the table 28 to identify the name, offset, and length
of each overlay in the overlay library file 24.  The overlay splitter
function 14 then reads through the overlay library file 24 splitting
out each overlay and each collection of fix-up records 32 associated
with each overlay.  The compression algorithm 16 then builds a
compressed file 34 for each overlay isolated in the split overlay
fi...