CODEWITHSUNDEEP
matlabbit-manipulation
Naseem
Naseem

Reputation: 39

Is there any faster way to perform bit rotate left for uint64 in Matlab

I want to optimize this Matlab function that performs bit rotate left for uint64 number

function Sh_x = ROL(x, nShift)
i = 1;
while i <= nShift
    y=reshape(dec2bin(typecast(swapbytes(x),'uint8'),8).',1,[]);
    bit = double(y(1))-48;
    x = bitset(x,64,0,'uint64');
    Sh_x = uint64(bitshift(x, 1,'uint64'));
    Sh_x = Sh_x + uint64(bit)* uint64(2)^0;
    x = Sh_x;
    i = i + 1;
end
end

Upvotes: 1

Views: 74

Answers (1)

Cris Luengo
Cris Luengo

Reputation: 60635

bitshift(x, nShift, 'uint64') shifts the 64-bit integer left by nShift values, discarding bits that overflow on the left side, and adding zeros on the right side. This leads to the left component of the expected output. What you're missing is the bits that overflowed on the left.

bitshift(x, nShift-64, 'uint64') shifts the 64-bit integer right by 64-nShift values, discarding values that exit on the right and adding zeros to the left. The remaining bits are the ones that exited left in the first left shift. This leads to the right component of the expected output.

Combine the two using bitor:

Sh_x = bitor(bitshift(x, nShift, 'uint64'), ...
             bitshift(x, nShift-64, 'uint64'), ...
             'uint64');

Upvotes: 3

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