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xz: Man page: Add more examples of LZMA2 options with BCJ filters.
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src/xz/xz.1
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src/xz/xz.1
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@ -6,7 +6,7 @@
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.\" This file has been put into the public domain.
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.\" You can do whatever you want with this file.
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.\"
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.TH XZ 1 "2024-01-22" "Tukaani" "XZ Utils"
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.TH XZ 1 "2024-01-23" "Tukaani" "XZ Utils"
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.
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.SH NAME
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xz, unxz, xzcat, lzma, unlzma, lzcat \- Compress or decompress .xz and .lzma files
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@ -1866,14 +1866,38 @@ Since the BCJ-filtered data is usually compressed with LZMA2,
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the compression ratio may be improved slightly if
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the LZMA2 options are set to match the
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alignment of the selected BCJ filter.
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For example, with the IA-64 filter, it's good to set
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.B pb=4
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or even
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Examples:
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.RS
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.IP \(bu 3
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IA-64 filter has 16-byte alignment so
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.B pb=4,lp=4,lc=0
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is good
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with LZMA2 (2^4=16).
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The x86 filter is an exception;
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it's usually good to stick to LZMA2's default
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four-byte alignment when compressing x86 executables.
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.IP \(bu 3
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RISC-V code has 2-byte or 4-byte alignment
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depending on whether the file contains
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16-bit compressed instructions (the C extension).
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When 16-bit instructions are used,
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.B pb=2,lp=1,lc=3
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or
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.B pb=1,lp=1,lc=3
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is good.
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When 16-bit instructions aren't present,
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.B pb=2,lp=2,lc=2
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is the best.
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.B readelf \-h
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can be used to check if "RVC"
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appears on the "Flags" line.
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.IP \(bu 3
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ARM64 is always 4-byte aligned so
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.B pb=2,lp=2,lc=2
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is the best.
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.IP \(bu 3
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The x86 filter is an exception.
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It's usually good to stick to LZMA2's defaults
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.RB ( pb=2,lp=0,lc=3 )
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when compressing x86 executables.
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.RE
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.IP ""
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All BCJ filters support the same
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.IR options :
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