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| DATE | 2014-12-14 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [LIU Comp Sci] NOTE ERROR:****Error in the Hamming notes on the final review
|
From owner-learn-outgoing-at-mrbrklyn.com Sun Dec 14 05:18:55 2014
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Date: Sun, 14 Dec 2014 05:18:53 -0500
From: Ruben Safir
To: Samir Iabbassen
Cc: learn-at-nylxs.com
Subject: [LIU Comp Sci] NOTE ERROR:****Error in the Hamming notes on the final review
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I'm looking at the hamming notes and I don't think it is right.
P4=P4 (x)? 0 (x)? 1 (x)??0 =1
Not accoding to how I see it
d8 d7 d6 d5 p4 d4 d3 d2 p3 d1 p2 p1
1100 1011 1010 1001 1000 0111 0110 0101 0100 0011 0010 0001 (r = 4)
1 0 1 0 1 0 0 1
P4 is 1 (x) 0 (x) 1 (x) 0 which is 0 (not 1)
The origianl party writen p4 -> p1
0010
After the flip of 5
0111
0010
0111
_____
0101
which is the 5th position...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I don't understand why this is being done BACKWARD though.
According to the Specification why are you not counting from
left to right from position 1 -> 12. It should look like this:
Draw the diagram
p1 p2 d1 p3 d2 d3 d4 p4 d5 d6 d7 d8
0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 (r = 4)
1 0 1 0 1 0 0 1
p1 ~ xor(d1,d2,d4,d5,d7) all 0001 positions
1 xor 0 xor 0 xor 1 xor 0 = 0
p2 ~ d1 d3 d4 d6 d7
1 xor 1 xor 0 xor 0 xor 0 = 0
p3 ~ d2 d3 d4 d8
0 1 0 1 = 0
p4 ~ d5 d6 d7 d8
1 0 0 1 = 0
Parity Bits are 0000
Total Message is
0010010001001
if 5 flips
p1 p2 d1 p3 d2 d3 d4 p4 d5 d6 d7 d8
0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 (r = 4)
1 0 1 0 0 0 0 1
the calculated parity is now
p1 10000 = 1
p2 11000 =0
p3 0101 = 0
p4 0001 = 1
0000
1001
____
1001 = d5
which means I need to read the question better because you asked to flip
posiiton 5 in the stream and not position 5 of the data .... but the
math all works.
NOTE: I couldn't understand why you reverse the order? Maybe this was
an IBM Bigended bits problem. I don't know but it makes it a PIA to map
out. And I thought it was inconstitant with the textbook but then I
notices that although the text maps the data data like I do, he then, at
the last step says
"Let us verify that this scheme works with an example. Assume that
the 8-bit input word is 00111001, with data bit D1 in the rightmost
position."
Damn - why do this backwards!
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