NAME

       nbdkit-swab-filter - nbdkit filter for swapping byte order

SYNOPSIS

        nbdkit --filter=swab PLUGIN [PLUGIN-ARGS...] [swab-bits=8|16|32|64]

DESCRIPTION

       "nbdkit-swab-filter" is a filter for nbdkit(1) which swaps bytes in the underlying plugin.

       One use for this is to read disk images which were formatted on the Atari Falcon, where
       the IDE controller is wired in reverse order.

EXAMPLE

   Swap bytes from a disk image
        nbdkit --filter=swab file file=disk.img

       The above command serves the disk image disk.img, swapping even and odd bytes:

        disk.img   0   1   2   3   4   5 ...
                     ╳       ╳       ╳
          output   1   0   3   2   5   4 ...

       This filter truncates the size of the plugin down to the alignment determined by swab-bits
       (since operating on an unaligned tail would be awkward).  If you need to round the image
       size up instead to access the last few bytes, combine this filter with
       nbdkit-truncate-filter(1); fortunately, sector-based disk images are already suitably
       sized.

       Note that this filter fails operations where the offset or count are not aligned to the
       swab-bits boundaries; if you need byte-level access, apply the nbdkit-blocksize-filter(1)
       before this one, to get read-modify-write access to individual bytes.

PARAMETERS

       swab-bits=8
           This turns off the filter.

       swab-bits=16
           This is the default setting which swaps pairs of bytes.  This is suitable when reading
           and writing to Atari Falcon drives.

       swab-bits=32
           This swaps the endianness of each 4 byte word in the disk, ie:

             input    0   1   2   3   4   5   6   7

            output    3   2   1   0   7   6   5   4

       swab-bits=64
           This swaps the endianness of each 8 byte word in the disk, ie:

             input    0   1   2   3   4   5   6   7

            output    7   6   5   4   3   2   1   0

           This can be used to make nbdkit-pattern-plugin(1) little endian instead of big endian.

FILES

       $filterdir/nbdkit-swab-filter.so
           The filter.

           Use "nbdkit --dump-config" to find the location of $filterdir.

VERSION

       "nbdkit-swab-filter" first appeared in nbdkit 1.22.

SEE ALSO

       nbdkit(1), nbdkit-file-plugin(1), nbdkit-pattern-plugin(1), nbdkit-filter(3),
       nbdkit-blocksize-filter(1).  nbdkit-truncate-filter(1).

AUTHORS

       François Revol

COPYRIGHT

       Copyright (C) 2020 François Revol

LICENSE

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