GNU bug report logs - #35205
[PATCH] Document IBM Z environment variables

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Ilya Leoshkevich <iii <at> linux.ibm.com>
To: bug-gzip <at> gnu.org
Cc: Ilya Leoshkevich <iii <at> linux.ibm.com>
Subject: [PATCH] Document IBM Z environment variables
Date: Tue,  9 Apr 2019 11:53:34 +0200

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

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