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83 lines
2.9 KiB
83 lines
2.9 KiB
6 years ago
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function decCoeffs = decodeHuff(huffSec, huffCodebook, huffLUT)
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% DECODEHUFF Huffman decoder stage
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%
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% decCoeffs = decodeHuff(huffSec, huffCodebook, huffLUT) performs huffman
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% decoding, where huffSec is a string of '1' and '0' corresponding to the
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% Huffman encoded stream, and huffCodebook is the index (0 to 12) of the
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% codebook used, as outputted by encodeHuff. huffLUT is the Huffman
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% look-up tables to be loaded using loadLUT.m. The output decCoeffs is
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% the decoded quantised (integer) values.
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%
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% CAUTION: due to zero padding the length of decCoeffs may be larger than
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% the length of the encoded sequence. Simply ignore values (they should
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% be equal to zero) that are outside the index range
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% [1:length(encoded sequence)].
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huffLUTi = huffLUT{huffCodebook};
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h=huffLUTi.invTable;
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huffCodebook=huffLUTi.codebook;
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nTupleSize=huffLUTi.nTupleSize;
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maxAbsCodeVal=huffLUTi.maxAbsCodeVal;
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signedValues=huffLUTi.signedValues;
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eos=0;%end of stream
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decCoeffs=[];
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huffSec=huffSec-48;
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streamIndex=1;
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while(~eos)%end of stream
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huffFailure=0;
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wordbit=0;
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r=1;%row indicator
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b=huffSec(streamIndex+wordbit);
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%decoding tuple according to inverse matrix
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while(1)
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b=huffSec(streamIndex+wordbit);
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wordbit=wordbit+1;
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rOld=r;
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r=h(rOld,b+1);%new index
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if((h(r,1)==0)&(h(r,2)==0))%reached a leaf (found a valid word)
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symbolIndex=h(r,3)-1;%The actual index begins from zero.
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streamIndex=streamIndex+wordbit;
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break;
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end
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end
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%decoding nTuple magnitudes
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if(signedValues)
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base=2*maxAbsCodeVal+1;
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nTupleDec=rem(floor(symbolIndex*base.^([-nTupleSize+1:1:0])),base);
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nTupleDec=nTupleDec-maxAbsCodeVal;
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else
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base=maxAbsCodeVal+1;
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nTupleDec=rem(floor(symbolIndex*base.^([-nTupleSize+1:1:0])),base);
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nTupleSignBits=huffSec(streamIndex:streamIndex+nTupleSize-1);
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nTupleSign=-sign(nTupleSignBits(:)'-0.5);
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streamIndex=streamIndex+nTupleSize;
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nTupleDec=nTupleDec.*nTupleSign;
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end
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escIndex=find(abs(nTupleDec)==16);
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if((huffCodebook==11)&&(sum(escIndex)))
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for i=1:length(escIndex)
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b=huffSec(streamIndex);
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N=0;
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%reading the escape seq, counting N '1's
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while(b)
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N=N+1;
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b=huffSec(streamIndex+N);
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end%last bit read was a zero corresponding to esc_separator..
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streamIndex=streamIndex+N;
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%reading the next N+4 bits
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N4=N+4;
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escape_word=huffSec(streamIndex+1:streamIndex+N4);
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nTupleDec(escIndex(i))=2^N4+bin2dec(num2str(escape_word));
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streamIndex=streamIndex+N4+1;
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end
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nTupleDec(escIndex)=nTupleDec(escIndex).*nTupleSign(escIndex);
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end
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decCoeffs=[decCoeffs nTupleDec];
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if (streamIndex>length(huffSec))
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eos=1;
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end
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end
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