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C Unleashed Chapter 18: Hamming Codes

 
 
jaysome
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      12-18-2007
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," 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

 
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Jack Klein
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      12-18-2007
On Mon, 17 Dec 2007 21:55:59 -0800, jaysome <(E-Mail Removed)>
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," 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,". It is
correct as "(12," 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
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Richard Heathfield
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      12-18-2007
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/...rata/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
 
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