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function [code] = arithenco(seq, count)
// This function encodes the given sequence using aritmetic coding
// Syntax
// 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
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