I have a 24-byte bitstring that I wish to unpack into 32 x 6-bit numbers.

I can do this using a kludge of unpacks and packs so:

$n = 1; 

print $n++, ':', ord( pack 'b6', $_ ) for unpack '(a6)*', unpack 'b*',
+ $x;;
1 : 39
2 : 31
3 : 19
4 : 52
5 : 4
6 : 21
7 : 30
8 : 16
9 : 55
10 : 57
11 : 57
12 : 50
13 : 42
14 : 63
15 : 45
16 : 0
17 : 31
18 : 33
19 : 0
20 : 36
21 : 62
22 : 51
23 : 53
24 : 21
25 : 51
26 : 14
27 : 55
28 : 50
29 : 51
30 : 41
31 : 63
32 : 19

[download]

But that's pretty inefficient and I'm looking for speed as it will be done many millions of times. vec's no good because it only does powers of 2-bits.

Is there a better pure perl way, or will I need to drop into C?

How would you do this efficiently in C anyway?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to unpacking 6-bit values by BrowserUk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.