HE/int2bit.m

function y = int2bit(x, N, MSBFirst)    
    %INT2BIT Convert integers to bits
    %
    %   Y = INT2BIT(X,N) converts each integer element in X to N
    %   column-wise bits in Y in 2's complement form, with the first or the
    %   top-most bit being the MSB (most significant bit). X can be a
    %   scalar, vector, matrix or an array with 3 dimensions. Y has same
    %   dimensions as X, except that the number of rows in Y are N times
    %   the number of rows in X. The datatype of X can be any of the
    %   built-in numeric types. When the datatype of X is -
    %    - a floating-point type, Y is of the same datatype.
    %    - a built-in unsigned integer type, datatype of Y is uint8.
    %    - a built-in signed integer type, datatype of Y is int8.
    %    - double, N must be no larger than 53.
    %    - single, N must be no larger than 24.
    %   When N is less than the minimum number of bits required to
    %   represent values in X i.e. N < ceil(log2(max(X)+1)), the least
    %   significant N bits are returned in Y.
    %
    %   Y = INT2BIT(X,N,MSBFIRST) specifies MSB orientation in MSBFIRST.
    %   When MSBFIRST is true, the first bit in each set of N column-wise
    %   bits in Y is the MSB; when MSBFIRST is false, the first bit in each
    %   set of N column-wise bits in Y is the LSB (least significant bit).
    %
    %   Examples:
    %
    %   A1 = [12 5];
    %   N1 = 4;
    %   B1 = int2bit(A1, N1);
    %
    %   A2 = int8([32 6 104; 120 66 9]);
    %   N2 = 8;
    %   msbFirst = false;
    %   B2 = int2bit(A2, N2, msbFirst);
    %
    %   A3 = randi([0,255], 4, 3, 2, 'uint16');
    %   N3 = 10;
    %   B3 = int2bit(A3, N3);
    %
    %   A4 = [153, -103, 103, -128];
    %   B4 = int2bit(A4, 8);         % 153 and -103 represent same bits
    %   B5 = int2bit(A4, 9);         % Use additional bit to have unique bits
    %
    %   See also BIT2INT.
    
    %   Copyright 2021-2022 The MathWorks, Inc.
    
    %#codegen
    
    narginchk(2,3);    
    if nargin == 2
        MSBFirst = true;
    else
        validateattributes(MSBFirst, {'logical','numeric'}, {'scalar','binary'}, '', 'MSBFirst');
    end
    
    if isfloat(x)
        % Output datatype is same as input's
        validateattributes(x, {'numeric'}, {'3d','nonempty','integer'}, '', 'X');
        if isa(x, 'double')
            maxN = 53;
        else
            maxN = 24;
        end
        validateattributes(N, {'numeric'}, {'scalar','positive','integer','<=',maxN}, '', 'N');
        useN = N;
        yType = x(1);
        isInputFloat = true;
    else        
        % Output datatype is uint8 or int8
        validateattributes(x, {'numeric'}, {'3d','nonempty'}, '', 'X');
        validateattributes(N, {'numeric'}, {'scalar','positive','integer'}, '', 'N');
        intClass = class(x);
        integerClasses = {'int8', 'uint8', 'int16', 'uint16', 'int32', 'uint32', 'int64', 'uint64'};
        integerNumBits = [8, 8, 16, 16, 32, 32, 64, 64];
        maxN = integerNumBits(strcmp(intClass, integerClasses));
        useN = min(N, maxN);
        if intClass(1) == 'u'
            yType = zeros(1, 'uint8');
        else
            yType = zeros(1, 'int8');
        end
        isInputFloat = false;
    end
    
    ySize = size(x);
    ySize(1) = ySize(1) * N;
    
    if coder.target('MATLAB')
        if isInputFloat
            % Matrix operations are faster, compared to element-wise
            % operations, in MATLAB simulation.

            if MSBFirst
                powOf2 = pow2(cast(-N+1:0, 'like', x));
            else
                powOf2 = pow2(cast(0:-1:(-N+1), 'like', x));
            end
            y = reshape(mod(floor(x(:) * powOf2), 2)', ySize);
        else
            % Use bitget() for built-in integers in sim to avoid
            % floating-point operations.
            if useN < N
                % When input integer value is negative and useN<N, then the
                % non-filling MSB bits must be ones rather than zeros.
                y1 = x<0;
                y = repelem(cast(y1,'like',yType),N,1);
            else
                y = zeros(ySize,'like',yType);
            end
            if MSBFirst
                for k=1:useN
                    y(N-k+1:N:end,:,:) = bitget(x, k);
                end
            else
                for k=1:useN
                    y(k:N:end,:,:) = bitget(x, k);
                end
            end
        end

    else
        % Vector operations are faster, compared to matrix operations which
        % require data reshape, in generated code.
        
        if isa(x, 'single')
            % bitget() is not supported for single. So, convert it to int32.
            intInput = cast(x, 'int32');
        else
            % Double, built-in integers
            intInput = x;
        end
        
        y = int2bitCG(intInput, N, MSBFirst, useN, yType, ySize);
    end
end

function y = int2bitCG(intInput, N, MSBFirst, useN, yType, ySize)
    % Code generation algorithm

    coder.internal.noRuntimeChecksInThisFunction;
    coder.inline('always');

    if useN == N
        y = coder.nullcopy(zeros(ySize, 'like', yType));
    elseif useN < N
        % When input integer value is negative and useN<N, then the
        % non-filling MSB bits must be ones rather than zeros.
        y1 = intInput<0;
        y = zeros(ySize,'like',yType); % Preallocating
        for ipage = 1:size(y1,3)
            tmp = cast(y1(:,:,ipage),'like',yType);
            y(:,:,ipage) = repelem(tmp,N,1);
        end
    else
        y = zeros(ySize,'like',yType);
    end

    ONE = coder.internal.indexInt(1);
    nIndexInt = coder.internal.indexInt(N);
    useNIndexInt = coder.internal.indexInt(useN);
    if isa(intInput,'double')
        bitgetclass = 'int64';
    else
        bitgetclass = class(intInput);
    end
    if MSBFirst
        for k=ONE:useNIndexInt
            tmp = bitget(intInput, k, bitgetclass);
            for i=ONE:numel(tmp)
                j = i*nIndexInt - k + ONE; % N-k+1:N:numel(y)
                y(j) = tmp(i);
            end
        end

    else
        for k=ONE:useNIndexInt
            tmp = bitget(intInput, k, bitgetclass);
            for i=ONE:numel(tmp)
                j = (i - ONE)*nIndexInt + k; % k:N:numel(y)
                y(j) = tmp(i);
            end
        end

    end
end