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README.txt

      1 zipalign -- zip archive alignment tool
      2 
      3 usage: zipalign [-f] [-v] <align> infile.zip outfile.zip
      4        zipalign -c [-v] <align> infile.zip
      5 
      6   -c : check alignment only (does not modify file)
      7   -f : overwrite existing outfile.zip
      8   -v : verbose output
      9   <align> is in bytes, e.g. "4" provides 32-bit alignment
     10   infile.zip is an existing Zip archive
     11   outfile.zip will be created
     12 
     13 
     14 The purpose of zipalign is to ensure that all uncompressed data starts
     15 with a particular alignment relative to the start of the file.  This
     16 allows those portions to be accessed directly with mmap() even if they
     17 contain binary data with alignment restrictions.
     18 
     19 Some data needs to be word-aligned for easy access, others might benefit
     20 from being page-aligned.  The adjustment is made by altering the size of
     21 the "extra" field in the zip Local File Header sections.  Existing data
     22 in the "extra" fields may be altered by this process.
     23 
     24 Compressed data isn't very useful until it's uncompressed, so there's no
     25 need to adjust its alignment.
     26 
     27 Alterations to the archive, such as renaming or deleting entries, will
     28 potentially disrupt the alignment of the modified entry and all later
     29 entries.  Files added to an "aligned" archive will not be aligned.
     30 
     31 By default, zipalign will not overwrite an existing output file.  With the
     32 "-f" flag, an existing file will be overwritten.
     33 
     34 You can use the "-c" flag to test whether a zip archive is properly aligned.
     35 
     36