the following commands demonstrate that either Digest::MD5 and gnu md5sum
are not compatible, or that i haven't got the backuppc md5 formula quite
right.  can anyone set me straight?  the commands below merely use the
filesize, and the whole file since it's <256K, feed them both to md5sum,
and show the result adjacent the filename.  the below shows /etc/papersize
and it's poolfile:

$ alias zcat=/usr/share/?ackup??/bin/BackupPC_zcat
> $ alias li=ls' -aFqldi --color --time-style=+%F" %a "%T'
> $ 1b()(printf \\x$(printf %x $1))
> $ 2b()(1b $(($1      /  256));1b $(($1%  256)))
> $ 4b()(2b $(($1%2**32/65536));2b $(($1%65536))) #write rightmost 4 bytes
> $ 4b 513         |xxd                           #4b sanity tests
> 0000000: 0000 0201                                ....
> $ 4b 65539       |xxd
> 0000000: 0001 0003                                ....
> $ 4b $((2**32-7))|xxd
> 0000000: ffff fff9                                ....
> $ 4b $((2**32+9))|xxd
> 0000000: 0000 0009                                ....
> $ md5sum --version|head -1
> md5sum (GNU coreutils) 8.13
> $ um()(s=$( cat $1|wc -c) m=$((4b $s; cat $1|sf)|md5sum);echo $(li $1) $m
> s=$s) #li & md5 of uncompressed argfile
> $ zm()(s=$(zcat $1|wc -c) m=$((4b $s;zcat $1|sf)|md5sum);echo $(li $1) $m
> s=$s) #li & md5 of  compressed argfile
> $ sf()if [ $s -le $(( 256*1024)) ];then
> cat                                     #select filedata for md5
> >   elif [ $s -le $((1024*1024)) ];then
> >      dd bs=128K count=1
> >      tail -c128K
> >   else
> >      dd bs=128K count=1
> >      dd bs=128K skip=6 count=1
> >   fi
> $ cat /etc/papersize
> a4
> $ xxd /etc/papersize
> 0000000: 6134 0a                                  a4.
> $ um /etc/papersize
> 349898 -rw-r--r-- 1 root root 3 2014-01-01 Wed 17:39:09 /etc/papersize
> 12cf0b6059ccc2701eb9e55277f161c2 - s=3
> $ zm /var/lib/backuppc/pc/127.0.0.1/0/f%2f/fetc/fpapersize
> 19720838 -rw-r----- 40 backuppc backuppc 11 2015-04-23 Thu 02:30:49
> /var/lib/backuppc/pc/127.0.0.1/0/f%2f/fetc/fpapersize
> 12cf0b6059ccc2701eb9e55277f161c2 - s=3
> $ zm /var/lib/backuppc/cpool/7/a/5/*991
> 19720838 -rw-r----- 40 backuppc backuppc 11 2015-04-23 Thu 02:30:49
> /var/lib/backuppc/cpool/7/a/5/7a59e82651106239413a38eb30735991
> 12cf0b6059ccc2701eb9e55277f161c2 - s=3
>
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