IBM Z patch (7a6f9c9) introduced 5 environment variables, which are
used to tune the compression and decompression with the DEFLATE
COMPRESSION CALL instruction. This patch adds texinfo documentation for
all of them.
* doc/gzip.texi(Environment): Add DFLTCC* environment variables.
---
doc/gzip.texi | 38 +++++++++++++++++++++++++++++++++++++-
1 file changed, 37 insertions(+), 1 deletion(-)
diff --git a/doc/gzip.texi b/doc/gzip.texi
index a6d9896..77b3a56 100644
--- a/doc/gzip.texi
+++ b/doc/gzip.texi
@@ -69,7 +69,7 @@ Free Documentation License''.
* Sample:: Sample output from @command{gzip}.
* Invoking gzip:: How to run @command{gzip}.
* Advanced usage:: Concatenated files.
-* Environment:: The @env{GZIP} environment variable
+* Environment:: Environment variables.
* Tapes:: Using @command{gzip} on tapes.
* Problems:: Reporting bugs.
* GNU Free Documentation License:: Copying and sharing this manual.
@@ -513,6 +513,42 @@ export PATH=/usr/bin
exec gzip -9 "$@@"
@end example
+The following environment variables are applicable only when using
+@command{gzip} on IBM Z mainframes supporting DEFLATE COMPRESSION CALL
+instruction:
+
+@table @option
+
+@item DFLTCC
+Whether DEFLATE COMPRESSION CALL should be used. Default value is @samp{1}.
+Set this to @samp{0} to disable DEFLATE COMPRESSION CALL altogether.
+
+@item DFLTCC_LEVEL_MASK
+Compression levels on which DEFLATE COMPRESSION CALL should be used.
+Represented as a bit mask in decimal or hexadecimal form, where each bit
+corresponds to a compression level. Default value is @samp{2}, which means
+level 1 only. In order to make use of DEFLATE COMPRESSION CALL by default,
that
+is, on levels 1-6, set this to @samp{0x7e}.
+
+@item DFLTCC_BLOCK_SIZE
+Size of deflate blocks produced by DEFLATE COMPRESSION CALL in bytes in decimal
+or hexadecimal form. Default value is @samp{1048576} (1 megabyte). When using
+DEFLATE COMPRESSION CALL to compress a file containing heterogeneous data (e.g.
+a @samp{.tar} archive containing text and binary files), setting this to a
+smaller value may improve compression ratio.
+
+@item DFLTCC_FIRST_FHT_BLOCK_SIZE
+Size of the first fixed deflate block produced by DEFLATE COMPRESSION CALL in
+bytes in decimal or hexadecimal form. Default value is @samp{4096} (4
+kilobytes). When using DEFLATE COMPRESSION CALL to compress a small file,
+setting this to a larger value may improve compression ratio.
+
+@item DFLTCC_RIBM
+Value of "Reserved for IBM" field of DEFLATE COMPRESSION CALL parameter block.
+Default value is @samp{0}.
+
+@end table
+
@node Tapes
@chapter Using @command{gzip} on tapes
@cindex tapes
--
2.21.0
