Although most tasks require a byte as their smallest quanta of information, sometimes one must go lower.

I have a binary file that is a stream of bits, not bytes. I must look for a first "frame" which is valid by some parameters. Lets say that the frame is 128 bits long, and it's valid if bits 9-14 are zeros, and bits 50-100 are ones.

The problem is: the file doesn't necessary start in the beginning of a frame, it can start in a middle ! So, I must churn it bit by bit looking for the valid frame.

My idea is to employ a "sliding window" search - go over the file, advancing by a bit each time and looking 128 bits "forward". However, I don't know what is the best way to do this. Any ideas ? How can I even read from the middle of a byte ? (Perl's lowest reading resolution is a byte, AFAIK)

In reply to perl bitology - breaking into bytes by spurperl

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.