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authorLasse Collin <lasse.collin@tukaani.org>2024-01-23 16:11:54 +0200
committerJia Tan <jiat0218@gmail.com>2024-01-23 23:05:47 +0800
commit6133a3f30049d3beaf7d22535b1e5d38e109be4e (patch)
treea1b1bd1fbe1abc99495e094c1c409a76182649b5 /src/xz/xz.1
parentliblzma: RISC-V filter: Use byte-by-byte access. (diff)
downloadxz-6133a3f30049d3beaf7d22535b1e5d38e109be4e.tar.xz
xz: Man page: Add more examples of LZMA2 options with BCJ filters.
Diffstat (limited to 'src/xz/xz.1')
-rw-r--r--src/xz/xz.138
1 files changed, 31 insertions, 7 deletions
diff --git a/src/xz/xz.1 b/src/xz/xz.1
index b489fd35..3c09309b 100644
--- a/src/xz/xz.1
+++ b/src/xz/xz.1
@@ -6,7 +6,7 @@
.\" This file has been put into the public domain.
.\" You can do whatever you want with this file.
.\"
-.TH XZ 1 "2024-01-22" "Tukaani" "XZ Utils"
+.TH XZ 1 "2024-01-23" "Tukaani" "XZ Utils"
.
.SH NAME
xz, unxz, xzcat, lzma, unlzma, lzcat \- Compress or decompress .xz and .lzma files
@@ -1866,14 +1866,38 @@ Since the BCJ-filtered data is usually compressed with LZMA2,
the compression ratio may be improved slightly if
the LZMA2 options are set to match the
alignment of the selected BCJ filter.
-For example, with the IA-64 filter, it's good to set
-.B pb=4
-or even
+Examples:
+.RS
+.IP \(bu 3
+IA-64 filter has 16-byte alignment so
.B pb=4,lp=4,lc=0
+is good
with LZMA2 (2^4=16).
-The x86 filter is an exception;
-it's usually good to stick to LZMA2's default
-four-byte alignment when compressing x86 executables.
+.IP \(bu 3
+RISC-V code has 2-byte or 4-byte alignment
+depending on whether the file contains
+16-bit compressed instructions (the C extension).
+When 16-bit instructions are used,
+.B pb=2,lp=1,lc=3
+or
+.B pb=1,lp=1,lc=3
+is good.
+When 16-bit instructions aren't present,
+.B pb=2,lp=2,lc=2
+is the best.
+.B readelf \-h
+can be used to check if "RVC"
+appears on the "Flags" line.
+.IP \(bu 3
+ARM64 is always 4-byte aligned so
+.B pb=2,lp=2,lc=2
+is the best.
+.IP \(bu 3
+The x86 filter is an exception.
+It's usually good to stick to LZMA2's defaults
+.RB ( pb=2,lp=0,lc=3 )
+when compressing x86 executables.
+.RE
.IP ""
All BCJ filters support the same
.IR options :