Reversible hex dump utility (aka `xxd`) xxd is a utility, bundled with vim, that has been used to encode answers to code golf problems on this site. It converts a binary file into a hex dump and back again.

Implement the xxd and xxd -r commands in the programming language(s) of your choice. Scoring is based on the character/byte lengths of a) your program(s) and b) any command line argument(s) necessary to switch a combined program between modes (they need not be -r). As in golf, lower scores are better.


For two separate programs: forward code + reverse code
For a combined program: combined code + sum(forward arguments) + sum(reverse arguments) - 2


Specification of the chosen xxd subset

The forward command (e.g. xxd) accepts 0 ≤ n ≤ 216 bytes from standard input and generates ceil(n / 16) lines of standard output in the following format (all hex digits lowercase):


Offset of the first encoded byte (format string "%07x:"); ends in "0"
At most 16 hex-encoded bytes, grouped into pairs (format string " %02x" for even bytes, "%02x" for odd bytes) and right-padded with spaces to 42 characters
The encoded bytes interpreted as ASCII characters, values not between 0x20 and 0x7e ('\40' and '\176') inclusive becoming "."
A newline ("\n"; "\r\n" allowed when standard output is in binary mode)


Minimal ungolfed C implementation:

#include &lt;stdio.h&gt;
int main() {
    unsigned char L[16];
    int t = 0, n, i, s;

    for (; (n = fread(L, 1, 16, stdin)); t += n) {
        printf("%07x:", t);
        s = 42;
        for (i = 0; i &lt; n; i++)
            s -= printf(i &amp; 1 ? "%02x" : " %02x", L[i]);
        printf("%*s", s, "");
        for (i = 0; i &lt; n; i++)
            putchar(L[i] &gt; '\37' &amp;&amp; L[i] &lt; '\177' ? L[i] : '.');
        printf("\n");
    }

    return 0;
}


The reverse command (e.g. xxd -r) accepts any unmodified output of the forward command (given a valid input to that command) and produces that original input.

Example usage

$ xxd &lt; /dev/null | wc -c
0
$ php -r 'echo join(range("\0",~"\0"));' | xxd
0000000: 0001 0203 0405 0607 0809 0a0b 0c0d 0e0f  ................
0000010: 1011 1213 1415 1617 1819 1a1b 1c1d 1e1f  ................
0000020: 2021 2223 2425 2627 2829 2a2b 2c2d 2e2f   !"#$%&amp;'()*+,-./
0000030: 3031 3233 3435 3637 3839 3a3b 3c3d 3e3f  0123456789:;&lt;=&gt;?
0000040: 4041 4243 4445 4647 4849 4a4b 4c4d 4e4f  @ABCDEFGHIJKLMNO
0000050: 5051 5253 5455 5657 5859 5a5b 5c5d 5e5f  PQRSTUVWXYZ[\]^_
0000060: 6061 6263 6465 6667 6869 6a6b 6c6d 6e6f  `abcdefghijklmno
0000070: 7071 7273 7475 7677 7879 7a7b 7c7d 7e7f  pqrstuvwxyz{|}~.
0000080: 8081 8283 8485 8687 8889 8a8b 8c8d 8e8f  ................
0000090: 9091 9293 9495 9697 9899 9a9b 9c9d 9e9f  ................
00000a0: a0a1 a2a3 a4a5 a6a7 a8a9 aaab acad aeaf  ................
00000b0: b0b1 b2b3 b4b5 b6b7 b8b9 babb bcbd bebf  ................
00000c0: c0c1 c2c3 c4c5 c6c7 c8c9 cacb cccd cecf  ................
00000d0: d0d1 d2d3 d4d5 d6d7 d8d9 dadb dcdd dedf  ................
00000e0: e0e1 e2e3 e4e5 e6e7 e8e9 eaeb eced eeef  ................
00000f0: f0f1 f2f3 f4f5 f6f7 f8f9 fafb fcfd feff  ................
$ xxd &lt;&lt;&lt; 'The quick brown fox jumps over the lazy dog.'
0000000: 5468 6520 7175 6963 6b20 6272 6f77 6e20  The quick brown 
0000010: 666f 7820 6a75 6d70 7320 6f76 6572 2074  fox jumps over t
0000020: 6865 206c 617a 7920 646f 672e 0a         he lazy dog..
$ xxd &lt;&lt;&lt; 'The quick brown fox jumps over the lazy dog.' | xxd -r
The quick brown fox jumps over the lazy dog.
Perl, 122 + 54 = 176 122 + 45 = 167

The forward script:

$/=$,;for(&lt;&gt;=~/.{1,16}/gs){$h="";$h.=sprintf"%*s%02x",++$m%2,"",ord for/./gs;
s/[^ -~]/./g;printf"%06x0:%-42s",$n++,$h;say}


And the reverse script:

/:(.+?)  /,print map{chr hex}$1=~/\w\w/gfor&lt;&gt;


(This one is interesting; there are all kinds of obscure bugs that can show up in the reverse script depending on the input, if you're not careful.)