update_model_adaptive.m

来自「多值自适应算数编码」· M 代码 · 共 38 行

function update_model_adaptive(symbol)

format long

global char_to_index index_to_char freq max_frequency cum_freq no_of_symbols
max_frequency=16383;
if(cum_freq(1)==max_frequency)
    cum=0;
    for ii=no_of_symbols:-1:1
        freq(ii)=fix((freq(ii)+1)/2);
        cum_freq(ii)=cum;
        cum=cum+freq(ii);
    end
end

ii=symbol;
while freq(ii)==freq(ii-1)
    ii=ii-1;
end

if(ii<symbol)
    ch_ii=index_to_char(ii);
    ch_symbol=index_to_char(symbol);
    index_to_char(ii)=ch_symbol;
    index_to_char(symbol)=ch_ii;
    char_to_index(ch_ii)=symbol;
    char_to_index(ch_symbol)=ii;
end

freq(ii)=freq(ii)+1; % was only ii+1 ??? but worked

while ii>1
    ii=ii-1;
    cum_freq(ii)=cum_freq(ii)+1;
end

%cum_freq(1:10)
%freq(1:10)