This commit was manufactured by cvs2svn to create tag 'FreeBSD-release/1.0'.

[unix-history] / gnu / usr.bin / gzip / algorithm.doc

diff --git a/gnu/usr.bin/gzip/algorithm.doc b/gnu/usr.bin/gzip/algorithm.doc
index 9c4b0c2..24f7619 100644 (file)
--- a/gnu/usr.bin/gzip/algorithm.doc
+++ b/gnu/usr.bin/gzip/algorithm.doc
@@ -48,6 +48,12 @@ match, thus speeding up the whole process. If compression ratio is more
 important than speed, zip attempts a complete second search even if
 the first match is already long enough.
 
 important than speed, zip attempts a complete second search even if
 the first match is already long enough.
 

+The lazy match evaluation is no performed for the fastest compression
+modes (speed options -1 to -3). For these fast modes, new strings
+are inserted in the hash table only when no match was found, or
+when the match is not too long. This degrades the compression ratio
+but saves time since there are both fewer insertions and fewer searches.
+

 
 2. gzip file format
 
 
 2. gzip file format
 


@@ -100,6 +106,23 @@ cleared indicating binary data. For systems which have different
 file formats for ascii text and binary data, the decompressor can
 use the flag to choose the appropriate format.
 
 file formats for ascii text and binary data, the decompressor can
 use the flag to choose the appropriate format.
 

+The extra field, if present, must consist of one or more subfields,
+each with the following format:
+
+  subfield id   : 2 bytes
+  subfield size : 2 bytes  (little-endian format)
+  subfield data
+
+The subfield id can consist of two letters with some mnemonic value.
+Please send any such id to jloup@chorus.fr. Ids with a zero second
+byte are reserved for future use. The following ids are defined:
+
+  Ap (0x41, 0x70) : Apollo file type information
+
+The subfield size is the size of the subfield data and does not
+include the id and the size itself. The field 'extra field length' is
+the total size of the extra field, including subfield ids and sizes.
+

 It must be possible to detect the end of the compressed data with any
 compression format, regardless of the actual size of the compressed
 data. If the compressed data cannot fit in one file (in particular for
 It must be possible to detect the end of the compressed data with any
 compression format, regardless of the actual size of the compressed
 data. If the compressed data cannot fit in one file (in particular for