how to do left and right bit rotation

Hi. I am trying to convert a matrix into 8 bit binary and then want to apply different bit rotations in different rows.e.g for row 1, 2bits will be rotated right and for row 2, 3 bits right rotation.

M=[2 32 45;3 54 12 98;134 245 69];
m1=(str2num(dec2bin(M)));
m=reshape(m1,[3 3]);
mm=m(:);
disp(dec2bin(bit_rotate(m,1),8))% error in this line.
%bitrotation function


function data = bit_rotate(data,nBits)
  dataBits = log2(double(intmax(class(data)))+1);  %# Number of bits in data
  nBits = rem(nBits,dataBits);  %# No need to rotate by dataBits bits or more
  if nBits == 0  %# No bit rotation needed, just return
    return
  end
  shiftedData = bitshift(data,nBits);              %# Bit shift the data
  lostData = bitxor(data,bitshift(shiftedData,-nBits));  %# Find the lost bits
  rotatedData = bitshift(lostData,nBits-sign(nBits)*dataBits);  %# Rotate them
  data = shiftedData+rotatedData;  %# Add the rotated bits to the shifted bits
end

[Walter Roberson]

The most efficient way is to use a pre-calculated lookup table.

For left rotation by 1 bit, if the value is < 128 then multiply it by 2. If it is >= 128 then subtract 128, multiply by 2, and add 1.

[sadiqa ilyas]

If I have 10100110

1 bit rotaion is 01001101

3 bit rotation is 00110101

and maybe I need 7 bit rotaion so will your

suggestion applicable? I have not used you method before thats why I want to clear the concept

[Walter Roberson]

function result = rotate_left_n(value, n)
   result = value;
   for K = 1 : n
       result = rotate_left_1(result);
   end
end

[sadiqa ilyas]

It gives error in line

result = rotate_left_1(result);

[Walter Roberson]

It is probably waiting for you to define a function rotate_left_1 according to the algorithm I suggested

https://www.mathworks.com/matlabcentral/answers/478957-how-to-do-left-and-right-bit-rotation#comment_742351

[sadiqa ilyas]

thanks

Answer 1

[Bruno Luong]

% Test example, 166 corresponds to your example of binary '10100110' 
M=[2 32 45;
   3 54 166;
   134 245 69]

rotfun = @(M,r) reshape(str2num(circshift(dec2bin(M,8),-r,2)),size(M))

rotfun(M,0)
rotfun(M,3)

Results:

ans =

          10      100000      101101
          11      110110    10100110
    10000110    11110101     1000101


ans =

       10000           1     1101001
       11000    10110001      110101
      110100    10101111      101010

[sadiqa ilyas]

Yhank u so much.It works.