/*
* This is the compress routine. It shows the basic algorithm for
* the compression programs used in this article. First, an input
* characters is loaded. The modeling routines are called to
* convert the character to a symbol, which has a high, low and
* range. Finally, the arithmetic coder module is called to
* output the symbols to the bit stream.
*/
void compress()
{
int i;
char c;
SYMBOL s;
FILE *compressed_file;
static char *input = "GLIB BATES";
compressed_file=fopen( "software/benchmarks/data/test.cmp", "wb" );
if ( compressed_file == NULL )
error_exit( "Could not open output file" );
puts( "Compressing..." );
initialize_output_bitstream();
initialize_arithmetic_encoder();
for ( i=0 ; ; )
{
c = input[ i++ ];
convert_int_to_symbol( c, &s );
encode_symbol( compressed_file, &s );
if ( c == '\0' )
break;
}
flush_arithmetic_encoder( compressed_file );
flush_output_bitstream( compressed_file );
fclose( compressed_file);
}
/*
* The main procedure is similar to the main found in ARITH1E.C. It has
* to initialize the coder and the model. It then sits in a loop reading
* input symbols and encoding them. One difference is that every 256
* symbols a compression check is performed. If the compression ratio
* falls below 10%, a flush character is encoded. This flushes the encod
* ing model, and will cause the decoder to flush its model when the
* file is being expanded. The second difference is that each symbol is
* repeatedly encoded until a successful encoding occurs. When trying to
* encode a character in a particular order, the model may have to
* transmit an ESCAPE character. If this is the case, the character has
* to be retransmitted using a lower order. This process repeats until a
* successful match is found of the symbol in a particular context.
* Usually this means going down no further than the order -1 model.
* However, the FLUSH and DONE symbols drop back to the order -2 model.
*
*/
void CompressFile(FILE *input,BIT_FILE *output,int argc,char *argv[])
{
SYMBOL s;
int c;
int escaped;
int flush = 0;
long int text_count = 0;
initialize_options( argc, argv );
initialize_model();
initialize_arithmetic_encoder();
for ( ; ; ) {
if ( ( ++text_count & 0x0ff ) == 0 )
flush = check_compression( input, output );
if ( !flush )
c = getc( input );
else
c = FLUSH;
if ( c == EOF )
c = DONE;
do {
escaped = convert_int_to_symbol( c, &s);
encode_symbol( output, &s );
} while ( escaped );
if ( c == DONE )
break;
if ( c == FLUSH ) {
flush_model();
flush = 0;
}
update_model( c );
add_character_to_model( c );
}
flush_arithmetic_encoder( output );
}
static void encode_arith_symbol(MscCoderArithModel *arithModel, PutBitContext *pb, int value) {
MscCoderArithSymbol arithSymbol;
// convert value to range symbol
convert_int_to_symbol(arithModel, value, &arithSymbol);
// encode symbol by arith encoder
encode_symbol(pb, &arithSymbol);
// update arithmetic model
update_model(arithModel, value);
}
