[FWP] Perl Golf, Ethernet to Token Ring MAC Address

[Alistair.McGlinchy@marks-and-spencer.com]

Hello All,

Recently I was playing with ethereal (from www.zing.org) and I needed to
convert MAC addresses as seen on a Token Ring into the address they
originally were on an Ethernet segment.  Token Ring's 6 byte MAC address is
big endian, where as Ethernet is read as little endian (or is it the other
way around?).  Hence I need to reverse the bits of each byte to convert from
one to the other. Eg  "123456789abc" in Token ring is represented as
482c6a1e593d on Ethernet. ( "12" in hex is 00010010 in binary, reversed is
01001000 which is "48" in hex, 34 => 2C, etc).
 
I thought this was a suitable candidate for some perl golf. Input and output
is a single 12 character text string matching /^[0-9a-f]{12}$/. Input is via
@ARGV . Output is to STDOUT. The real-world code I used looked (a bit) like
this:

my
%reverse_bits=("0","0","1","8","2","4","3","c","4","2","5","a","6","6","7","
e","8","1","9","9","a","5","b","d","c","3","d","b","e","7","f","f");

print Eth_2_Tok($ARGV[0]);

# Explicit Method
sub Eth_2_Tok { 
 	@nibble_array = split //, $_[0];
 	my $answer;
 	while (@nibble_array) {
 		my $high_nib=shift @nibble_array;
 		my $low_nib=shift @nibble_array;
 		$answer.=$reverse_bits{$low_nib}.$reverse_bits{$high_nib}
 	}
 	return $answer;
 } 

My solutions are written below:

<SPOILER WARNING> 



























I "golf"ed the explicit method down to a disappointing 82 chars using a
regular expression with:

%c=split//,'0018243C425A667E8199A5BDC3DBE7FF';$_=pop;s/(.)(.)/$c{$2}$c{$1}/g
;print

But was amazed that a pack/unpack combination could do better at 61 chars.

for(unpack"B8"x6,pack"H12",pop){print unpack"H*",pack"b8",$_}

Any suggestions/improvements ?



Alistair McGlinchy 

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