function [S, sfc, G] = AACquantizer(frameF, frameType, SMR)
%Implementation of Quantizer
%   Usage [S, sfc, G] = AACquantizer(frameF, frameType, SMR), where:
%       Inputs
%       - frameF is the frame in the frequency domain, in MDCT coefficients
%       representation containing only one of the audio channels stored in
%       a vector of length 1024
%       - frameType is the type of the current frame in string
%       representation, can be one of "OLS" (ONLY_LONG_SEQUENCE), "LSS"
%       (LONG_START_SEQUENCE), "ESH" (EIGHT_SHORT_SEQUENCE), "LPS"
%       (LONG_STOP_SEQUENCE)
%        - SMR is the signal to mask ratio array of dimensions 42X8 for
%       EIGHT_SHORT_SEQUENCE frames and 69X1 otherwise
%
%       Output
%        - S are the MDCT quantization symbols of one audio channel stored
%        in a vector of length 1024
%        - sfc are the scalefactors per band stored in an array of
%        dimensions NBX8 for EIGHT_SHORT_SEQUENCE frames and NBX1
%        otherwise, where NB is the number of bands
%        - G is the global gain stored in an array of dimensions 1X8 for
%        EIGHT_SHORT_SEQUENCE frames and a single value otherwise

    % Declares constant numbers of bands for long and short windows
    LONG_WINDOW_NUMBER_OF_BANDS = 69;
    SHORT_WINDOW_NUMBER_OF_BANDS = 42;

    % Declares persistent variable holding the TNS tables and initializes if empty
    persistent TNSTables;
    if isempty(TNSTables)
        TNSTables = load('TableB219.mat');
    end

    if ~strcmp(frameType, 'ESH')
        T(LONG_WINDOW_NUMBER_OF_BANDS, 1) = 0;
        quantCoeff(LONG_WINDOW_NUMBER_OF_BANDS, 1) = 0;
        sfc(LONG_WINDOW_NUMBER_OF_BANDS, 1) = 0;
        initialQuantCoeff = 16 * log2(max(frameF) ^ (3 / 4) / 8191) / 3;
        for band = 1:LONG_WINDOW_NUMBER_OF_BANDS
            frameWlow = TNSTables.B219a(band, 2) + 1;
            frameWhigh = TNSTables.B219a(band, 3) + 1;
            subFrameF = frameF(frameWlow:frameWhigh);

            T(band) = sumsqr(subFrameF) ./ SMR(band);

            % Calculates an initial quantization coefficient and attempts
            % quantization
            quantCoeff(band) = initialQuantCoeff;
            S(frameWlow:frameWhigh, 1) = sign(subFrameF) .* floor(( ...
                abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
                .^ (3 / 4) + 0.4054);

            % Calculates dequantized frame samples
            frameFDequant = sign(S(frameWlow:frameWhigh, 1)) .* ...
                abs(S(frameWlow:frameWhigh, 1)) .^ ...
                (4 / 3) .* 2 ^ (quantCoeff(band) / 4);

            % Calculates current quantization error
            quantErr = sumsqr(subFrameF - frameFDequant);

            % Gradually increases the quantization coefficient
            while quantErr < T(band) && (band < 2 || ...
                    (quantCoeff(band) - quantCoeff(band - 1) + 1) <= 60)
                quantCoeff(band) = quantCoeff(band) + 1;
                S(frameWlow:frameWhigh) = sign(subFrameF) .* round(( ...
                    abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
                    .^ (3 / 4) + 0.4054);

                frameFDequant = sign(S(frameWlow:frameWhigh, 1)) .* ...
                    abs(S(frameWlow:frameWhigh, 1)) .^ ...
                    (4 / 3) .* 2 ^ (quantCoeff(band) / 4);

                quantErr = sumsqr(subFrameF - frameFDequant);
            end
            
            % Undoes the last incrementation
            if quantCoeff(band) ~= initialQuantCoeff
                quantCoeff(band) = quantCoeff(band) - 1;
                S(frameWlow:frameWhigh) = sign(subFrameF) .* round(( ...
                    abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
                    .^ (3 / 4) + 0.4054);
            end

            if band == 1
                sfc(band) = quantCoeff(band);
            else
                sfc(band) = quantCoeff(band) - quantCoeff(band - 1);
            end
        end
        G = quantCoeff(1);
    else
        T(SHORT_WINDOW_NUMBER_OF_BANDS, 1) = 0;
        quantCoeff(SHORT_WINDOW_NUMBER_OF_BANDS, 1) = 0;
        sfc(SHORT_WINDOW_NUMBER_OF_BANDS, 8) = 0;
        G(1, 8) = 0;
        for subFrameIndex = 1:8
            currFrameStart = (subFrameIndex - 1) * 128 + 1;
            currFrameStop = currFrameStart + 127;
            subFrame = frameF(currFrameStart:currFrameStop);
            initialQuantCoeff = 16 * log2(max(subFrame) ^ (3 / 4) / 8191) / 3;
            for band = 1:SHORT_WINDOW_NUMBER_OF_BANDS
                frameWlow = TNSTables.B219b(band, 2);
                frameWhigh = TNSTables.B219b(band, 3);
                subFrameF = subFrame(frameWlow + 1:frameWhigh + 1);

                T(band) = sumsqr(subFrameF) ./ SMR(band);

                % Calculates an initial quantization coefficient and attempts
                % quantization
                quantCoeff(band) = initialQuantCoeff;
                S(currFrameStart + frameWlow:currFrameStart + frameWhigh, 1) = sign(subFrameF) .* floor(( ...
                    abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
                    .^ (3 / 4) + 0.4054);

                % Calculates dequantized frame samples
                frameFDequant = sign(S(currFrameStart + frameWlow: ...
                    currFrameStart + frameWhigh, 1)) .* abs(S( ...
                    currFrameStart + frameWlow:currFrameStart + frameWhigh, 1) ...
                    ) .^ (4 / 3) .* 2 ^ (quantCoeff(band) / 4);

                % Calculates current quantization error
                quantErr = sumsqr(subFrameF - frameFDequant);

                % Gradually increases the quantization coefficient
                while quantErr < T(band) && (band < 2 || ...
                        (quantCoeff(band) - quantCoeff(band - 1) + 1) <= 60)
                    quantCoeff(band) = quantCoeff(band) + 1;
                    S(currFrameStart + frameWlow:currFrameStart + frameWhigh) = sign(subFrameF) .* round(( ...
                        abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
                        .^ (3 / 4) + 0.4054);

                    frameFDequant = sign(S(currFrameStart + frameWlow: ...
                        currFrameStart + frameWhigh, 1)) .* abs(S( ...
                        currFrameStart + frameWlow:currFrameStart + frameWhigh, 1) ...
                        ) .^ (4 / 3) .* 2 ^ (quantCoeff(band) / 4);
                    
                    quantErr = sumsqr(subFrameF - frameFDequant);
                end
                
                % Undoes the last incrementation
                if quantCoeff(band) ~= initialQuantCoeff
                    quantCoeff(band) = quantCoeff(band) - 1;
                    S(currFrameStart + frameWlow:currFrameStart + frameWhigh) = sign(subFrameF) .* round(( ...
                        abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
                        .^ (3 / 4) + 0.4054);
                end
                
                if band == 1
                    sfc(band, subFrameIndex) = quantCoeff(band);
                else
                    sfc(band, subFrameIndex) = quantCoeff(band) - quantCoeff(band - 1);
                end
            end
            G(1, subFrameIndex) = quantCoeff(1);
        end
    end
end