binary addition for 128 bit

I want to addition to 128binary bit represent in char.

[Geoff Hayes]

Radwa - please clarify your statement. Do you have two 128 character strings of ones and zeros that you wish to add as if they were 128-bit integers? If so, are the integers signed or unsigned? What algorithm are you using to implement this?

[Radwa]

I have 64 binary bits in form of 1*64 char I want to add 1 to it

Answer 1

[Geoff Hayes]

Radwa - try the following. There could be more efficient algorithms, but this is pretty straightforward. Just save all of the code to a file named binaryAdd.m.

 function [sRes] = binaryAdd(s1,s2)

    numBits = 64;

    % ensure that the strings are the correct size
    s1 = validateBits(s1,numBits);
    s2 = validateBits(s2,numBits);

    % add the two strings together
    sRes = repmat('0',1,numBits);

    % indicator for a remainder
    haveRem = 0;

    % iterate over each bit (assume that right-most bit is least significant bit)
    for k = numBits:-1:1
        % sum the kth bits
        v = str2double(s1(k)) + str2double(s2(k)) + haveRem;

        haveRem = 0;

        % ignore case of the sum being zero, need only check for 1, 2, or 3
        if v==1
            sRes(k) = '1';
        elseif v>1
            sRes(k) = num2str(mod(v,2));
            haveRem = 1;
        end
    end

    if haveRem
        sRes = [repmat('0',1,numBits-1) '1' sRes];
    end

end

function [s] =  validateBits(s,numBits)

    if length(s)>numBits
        s = s(1:numBits);
    elseif length(s)<numBits
        s = [repmat('0',1,numBits-length(s)) s];
    end

end

For your example,

 binaryAdd(repmat('1',1,64),'1')

the result is a 128-bit string

 ans = 
 00000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000

[Radwa]

thanks , what can I do If I want to add 1 to the 128 bit ( I want to put the one in the most significant bit)

[Geoff Hayes]

If the most significant bit is zero and you add one to it, then the zero changes to a one. If the most significant bit is a one and you add a one to it, then what should happen? Should the result roll over? Should the result now be 256 bits? Should the value stay the same?

[Radwa]

Mu idea that I have counter with length 64 bit ( 1*64 char) I want to add 1 in every iteration in the counter and if reach the maximum all of them is 1 I want to begin from all zeros

[Radwa]

yes I want to have the same shape or that shape counter= {' '88' '99' 'aa' 'bb' 'cc' 'dd' 'ee' 'ff'};