Assign index value to bits in cyclic order

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 !!

[Jan]

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]

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

Answer 1

[Andrei Bobrov]

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))'

[Nil]

thanks much andrei bobrov..i will verify it..just one question

k = (0:2)'

s1 = reshape(regexprep(s,' ',''),2,[])'

P = N(find(N(:,1) == p)+(0:n-1))'

is this ' sign needed after each bracket?

[Andrei Bobrov]

transpose of of the array

[Nil]

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