/*
* This expansion routine demonstrates the basic algorithm used for
* decompression in this article. It first goes to the modeling
* module and gets the scale for the current context. (Note that
* the scale is fixed here, since this is not an adaptive model).
* It then asks the arithmetic decoder to give a high and low
* value for the current input number scaled to match the current
* range. Finally, it asks the modeling unit to convert the
* high and low values to a symbol.
*/
void expand()
{
FILE *compressed_file;
SYMBOL s;
char c;
int count;
compressed_file=fopen( "software/benchmarks/data/test_comp.cmp", "rb" );
if ( compressed_file == NULL )
error_exit( "Could not open output file" );
puts( "Decoding..." );
printf( "Incoming characters: " );
initialize_input_bitstream();
initialize_arithmetic_decoder( compressed_file );
for ( ; ; )
{
s.scale = 11;
count = get_current_count( &s );
c = convert_symbol_to_int( count, &s );
if ( c == '\0' )
break;
remove_symbol_from_stream( compressed_file, &s );
putc( c, stdout );
}
putc( '\n', stdout );
}
/*
* The main loop for expansion is very similar to the expansion
* routine used in the simpler compression program, ARITH1E.C. The
* routine first has to initialize the the arithmetic coder and the
* model. The decompression loop differs in a couple of respect.
* First of all, it handles the special ESCAPE character, by
* removing them from the input bit stream but just throwing them
* away otherwise. Secondly, it handles the special FLUSH character.
* Once the main decoding loop is done, the cleanup code is called,
* and the program exits.
*
*/
void ExpandFile(BIT_FILE *input,FILE *output,int argc,char *argv[])
{
SYMBOL s;
int c;
int count;
initialize_options( argc, argv );
initialize_model();
initialize_arithmetic_decoder( input );
for ( ; ; ) {
do {
get_symbol_scale( &s );
count = get_current_count( &s );
c = convert_symbol_to_int( count, &s );
remove_symbol_from_stream( input, &s );
} while ( c == ESCAPE );
if ( c == DONE )
break;
if ( c != FLUSH )
putc( (char) c, output );
else
flush_model();
update_model( c );
add_character_to_model( c );
}
}
static int decode_arith_symbol(MscCoderArithModel *arithModel, GetBitContext *gb) {
MscCoderArithSymbol arithSymbol;
int count, value;
// get range symbol
get_symbol_scale(arithModel, &arithSymbol);
// get value for symbol
count = get_current_count(&arithSymbol);
value = convert_symbol_to_int(arithModel, count, &arithSymbol);
// remove symbol from stream
remove_symbol_from_stream(gb, &arithSymbol);
// update arithmetic coder model
update_model(arithModel, value);
return value;
}
