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Diffstat (limited to 'macros/arithenco.sci')
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diff --git a/macros/arithenco.sci b/macros/arithenco.sci new file mode 100644 index 0000000..a463afa --- /dev/null +++ b/macros/arithenco.sci @@ -0,0 +1,166 @@ +function [code] = arithenco(seq, count) +// This function encodes the given sequence using aritmetic coding + +// Calling sequence +// CODE = ARITHENCO(SEQ, COUNT) + +// Description +// CODE = ARITHENCO(SEQ, COUNT) encodes the given sequence (SEQ) using arithmetic coding. +// COUNT is vector whihc gives information about the source statistics (i.e. frequency of each symbol in the source alphabet) +// CODE is the binary arithmetic code +// Source Alphabet is assumed to be {1,2,....N} where N is a positive integer +// Therefore, sequence should be finite and positive +// Length of the COUNT should match the length of the source alphabet + +// Examples +// counts = [40 1 9]; +// len = 4; +// seq = [1 3 2 1] +// code = arithenco(seq,counts); +// disp(code) + +// Bibliography +// Sayood, K., Introduction to Data Compression, Morgan Kaufmann, 2000, Chapter 4, Section 4.4.3. + +// See also +// arithdeco + +// Authors +// Pola Lakshmi Priyanka, IIT Bombay// + + +//*************************************************************************************************************************************// + + //Input argument check + [outa,inpa]=argn(0); + if(~inpa==2) + error("comm:arithenco:Wrong number of Input Arguments"); + end + + [row_seq,col_seq]=size(seq); + [row_sta,col_sta]=size(count); + + // Check to make sure that sequence is 1D + if(~(row_seq==1|col_seq==1)) + error("comm:arithenco: Invalid dimensions: Input Sequence should be 1D "); + end + + // Check for source statistics matrix + if(~(row_sta==1|col_sta==1)) + error("comm:arithenco: Invalid dimensions: Argument 2 should be 1D "); + end + + if(~isreal(seq) | or(seq<0) ) + error("comm:arithenco: Input sequence should be finite positive integer"); + end + + if(~isreal(count) | or(count<0) ) + error("comm:arithenco: Source statistics should be finite positive integer"); + end + + //Check if number of elements in source alphabet is equal to dimensions of source statistics matrix + if max(seq) > length(count) + error("comm:arithenco:Source alphabet size does not match with source statistics size"); + end + + //Check the incoming orientation and adjust if necessary + + if (row_seq > 1), + seq = seq.'; + end + + if (row_sta > 1), + count = count.'; + end + + [row_s,col_s]=size(seq); + [row_c,col_c]=size(count); + + //Calculate the cumulative count + cum_count=[0,cumsum(count)]; + scale3=0; + total_count=cum_count(length(cum_count)); + + //Initialization + m=ceil(log2(total_count)) + 2; + low=zeros(1,m); + up=ones(1,m); + dec_low=0; + dec_up=2^m-1; + code_len = length(seq) * ( ceil(log2(length(count))) + 2 ) + m; + code = zeros(1, code_len); + code_index = 1; + + + // For each bit in the seq + + for k=1:length(seq) + symbol = seq(k); + // Compute the lower and upper bounds + dec_low_new = dec_low + floor( (dec_up-dec_low+1)*cum_count(symbol+1-1)/total_count ); + dec_up = dec_low + floor( (dec_up-dec_low+1)*cum_count(symbol+1)/total_count )-1; + dec_low = dec_low_new; + + for i=1:m + low(i)=strtod(part(dec2bin(dec_low,m),i)) + end + for i=1:m + up(i)=strtod(part(dec2bin(dec_up,m),i)) + end + + //Loop while E1, E2 or E3 condition + while(isequal(low(1),up(1))) | (isequal(low(2),1) & isequal(up(2),0)) + // Check for E1 or E2 condition + if isequal(low(1),up(1)) then //E1 or E2 holds + // Transmit MSB + b=low(1); + code(code_index) = b; + code_index = code_index + 1; + + //Left shift + low=[low(2:m) 0]; + up=[up(2:m) 1]; + while (scale3>0) + code(code_index) = bitxor(b,1); + code_index = code_index + 1; + scale3 = scale3-1; + end + end + if (isequal(low(2),1) & isequal(up(2),0)) then //for E3 + //left shift + low=[low(2:m),0]; + up=[up(2:m),1]; + //disp(up,low,"up,low"); + + low(1)=bitxor(low(1),1); + up(1)=bitxor(up(1),1); + + scale3=scale3+1; + end + end + dec_low=0;dec_up=0; + for i=1:length(low) + dec_low=dec_low+low(i)*2^(length(low)-i); + dec_up=dec_up+up(i)*2^(length(up)-i); + end + end + if scale3==0 then + code(code_index:code_index + m - 1) = low; + code_index = code_index + m; + end + if ~scale3==0 then + b=low(1); + code(code_index)=b; + code_index = code_index + 1; + + while (scale3>0) + code(code_index) = bitxor(b,1); + code_index = code_index + 1; + scale3 = scale3-1; + end + + code(code_index:code_index+m-2) = low(2:m); + code_index = code_index + m - 1; + end +code = code(1:code_index-1); +endfunction |