C Unleashed Chapter 18: Hamming Codes

Discussion in 'C Programming' started by jaysome, Dec 18, 2007.

  1. jaysome

    jaysome Guest

    In C Unleashed, Chapter 18, in the section titled "Correcting the
    Errors: Hamming Codes", I was confused by the "(12,4)" reference. In
    one paragraph, the author says that:

    "In general, this two-value representation is referred to as (c,d),
    where d is the original number of data bits and c in the number of
    bits in the encoded word, including the Hamming parity bits."

    In a few paragraphs later, it states:

    "We will take a look at the (12,4) Hamming code..."

    But in Figure 18.4 (which includes "(12,4)" in its caption), there are
    8 data bits.

    Shouldn't "(12,4)" be "(12,8)" everywhere in this section? Or am I
    missing something? I looked in the errata and did not see any such
    correction.

    I only ask because I found this section in particular and the entire
    Chapter 18 in general and the entire book overall to be very
    informative, and I know some of the regulars here contributed to this
    book, which I consider to be a gem.

    --
    jay
    jaysome, Dec 18, 2007
    #1
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  2. jaysome

    Jack Klein Guest

    On Mon, 17 Dec 2007 21:55:59 -0800, jaysome <>
    wrote in comp.lang.c:

    > In C Unleashed, Chapter 18, in the section titled "Correcting the
    > Errors: Hamming Codes", I was confused by the "(12,4)" reference. In
    > one paragraph, the author says that:
    >
    > "In general, this two-value representation is referred to as (c,d),
    > where d is the original number of data bits and c in the number of
    > bits in the encoded word, including the Hamming parity bits."
    >
    > In a few paragraphs later, it states:
    >
    > "We will take a look at the (12,4) Hamming code..."
    >
    > But in Figure 18.4 (which includes "(12,4)" in its caption), there are
    > 8 data bits.
    >
    > Shouldn't "(12,4)" be "(12,8)" everywhere in this section? Or am I
    > missing something? I looked in the errata and did not see any such
    > correction.
    >
    > I only ask because I found this section in particular and the entire
    > Chapter 18 in general and the entire book overall to be very
    > informative, and I know some of the regulars here contributed to this
    > book, which I consider to be a gem.


    Oops, sorry about that. You are absolutely correct, and, as far as I
    know, the first person in seven and a half years to catch that. I'm
    pretty sure that doesn't mean that you're the only one to read my
    chapter. At least I hope it doesn't.

    Both "(12,4)" references on page 813 should be "(12,8)". It is
    correct as "(12,8)" on page 817, which I believe is the only other
    place it appears.

    It is also correct in the description on my web page for Chapter 18,
    http://jk-technology.com/C_Unleashed/code_list.html

    I don't think I can add this to Richard's errata page, since he has
    said he is no longer associated with the ISP and does not even know
    why the pages are still there.

    I will try to add all the contents of his Chapter 18 errata page,
    which I have captured, and the error you found, as well as a few
    others I've received over time to my page in the near future.

    And, of course, thanks for the kind words.

    --
    Jack Klein
    Home: http://JK-Technology.Com
    FAQs for
    comp.lang.c http://c-faq.com/
    comp.lang.c++ http://www.parashift.com/c -faq-lite/
    alt.comp.lang.learn.c-c++
    http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html
    Jack Klein, Dec 18, 2007
    #2
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  3. Jack Klein said:

    <snip>

    > I don't think I can add this to Richard's errata page, since he has
    > said he is no longer associated with the ISP and does not even know
    > why the pages are still there.


    Some time ago, I did some Search And Rescue on these pages, and they are
    now safely copied to a place where I can update them as required. See
    http://www.cpax.org.uk/prg/portable/c/unleashed/errata/ech18.php - which
    now contains a reference to jaysome's discovery.

    --
    Richard Heathfield <http://www.cpax.org.uk>
    Email: -http://www. +rjh@
    Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
    "Usenet is a strange place" - dmr 29 July 1999
    Richard Heathfield, Dec 18, 2007
    #3
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