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Assign index value to bits in cyclic order

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Nil
Nil 2012-3-13
Hi,
I am working on implementing following logic in matlab
I calculating index variable value based on length of my ciphertext
Index Variable P=Mod(l,3) where l is length of ciphertext after converting it into binary
Say ciphertext is 11001011 01111010 10101010 10011001 01010101
This data is five bytes. So l=5 therefore p=2 ((Mod(l,3)) &
then I want to assign index variable to the bits of cipher text in cylic order based on calculated value of index variable
P=0 then
P=1 then
P=2 then after this again p=0
Operation IndexVariable,P
(11) 2
(00) 0
(10) 1
(11) 2
(01) 0
(11) 1
(10) 2
(10) 0
(10) 1
(10) 2
(10) 0
(10) 1
so on………
please provide me directions..
Thanks in Advance !!
  2 个评论
Jan
Jan 2012-3-13
I understand the question until "p=2 ((Mod(l,3)) &". What does this mean? I do not get the meaning of the next sentence "the I want..." and "P=0 then P=1 then P=2 then". What is the "Operation" and what does the comma mean in "IndexVariable,P".
Nil
Nil 2012-3-13
Hi Jan Simon..thanks for your comment on question
Here after converting cipher text to bytes, I am calculating index variable (called as p) & formula is MOD(No of Bytes,3).. I have ciphertext length as 5 bytes so Index Variable (p) is 2.. I will always have index varaible values as 0 or 1 or 2 which will be based on no. of Bytes
Say ciphertext is 11001011 01111010 10101010 10011001 01010101
This data is five bytes there for inde variable is 2
11001011 01111010 10101010 10011001 01010101
Now
for first two bits (11) , index variable to be assigned as 2
for next two bits (00), index variable to be assigned as 0
for next two bits (10), index variable to be assigned as 1
for next two bits (11), index variable to be assigned as 2..so on till end of my bits.
------------------------------------------------------
Other Example
Ciphertet with Three Bytes 11001011 01111010 10101010
Index Variable (p) will be 0
for first two bits (11) , index variable to be assigned as 0
for next two bits (00), index variable to be assigned as 1
for next two bits (10), index variable to be assigned as 2
for next two bits (11), index variable to be assigned as 0..
so on till end of my bits..
I hope it clarify my question..I have tried out some coding which is posted yesterday in other post tilted as "loop help" but struggling in assigning index variable to bits

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2012-3-13
s = '11001011 01111010 10101010 10011001 01010101'
p = rem(numel(regexp(s,' [01]'))+1,3)
k = (0:2)'
s1 = reshape(regexprep(s,' ',''),2,[])'
n = size(s1,1)
N = k(:,ones(fix((n+1)/3)+1,1))
P = N(find(N(:,1) == p)+(0:n-1))'
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Nil
Nil 2012-3-14
hi andrei.it's working as expected thanks for your help.
Here getting s1 as below, I want in following format just to extract bits..
I have tried it with reshape and transpose but not picking up correct bit values
s1 =
11
00
10
11
01
11
10
10
10
10
10
10
10
01
10
01
How to convert s1 as
[1 1 0 0 1 0 1 1 0 1 1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 1 0 0 1]
so
s1(1) will be 1
s1(3) will be 0
s1(5) will be 1

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