getbits.c

speech signal process tools

/*
 ********************************************************************************
 *
 *  This material contains proprietary software of Entropic Speech, Inc.
 *  Any reproduction, distribution, or publication without the the prior
 *  written permission of Entropic Speech, Inc. is strictly prohibited.
 *  Any public distribution of copies of this work authorized in writing
 *  by Entropic Speech, Inc. must bear the notice:
 *
 *     "Copyright (c) 1987 Entropic Speech, Inc.; all rights reserved"
 *
 *  Program: getbits
 *
 *  Written by: Jim Elliott
 *
 *  Reads serial bitstream file for decode program.
 *
 ********************************************************************************
 */

/*
 *  SCCS program and date keywords.
 */

#ifndef lint
static char *sccs_id = "@(#)getbits.c	1.2	11/25/87 ESI";
#endif

/*
 *  System include files.
 */

#include <stdio.h>

/*
 *  ESPS include files.
 */

#include <esps/esps.h>
#include <esps/fea.h>
#include <esps/fea2kb.h>

/*
 ********************************************************************************
 *  Subroutine to read a bit field of a specified length from the input
 *  bitstream.
 ********************************************************************************
 */

get_bits( fea2kb_rec, ih, ifp, nbits, debug, dfp, field, cnt, stuff_inhib, stf )

FILE *dfp, *ifp;
int *cnt, debug, *field, nbits, *stf, stuff_inhib;
struct fea2kb *fea2kb_rec;
struct header *ih;
{
    unsigned long
	bit,			/* On/off bit indicator */
	c;			/* Unsigned copy of bit field */

    static int
	init = YES,		/* Flag for initial entry */
	ones_cnt,		/* Consecutive one's counter */
	state,			/* State of bitstream (1 or 0) */
	sync_ones;		/* Number of ones in sync code */

    static unsigned long
	buf,			/* Bitstream buffer */
	mask;			/* Mask for current bit */

    if ( init )
    {
	init = NO;
	if ( stuff_inhib )
	    sync_ones = nbits - 2;

	fill_buffer( fea2kb_rec, ih, ifp, debug, dfp, &buf, &mask );
    }

    c = 0;
    *cnt = nbits;

    for ( ; nbits >= 1; nbits-- )
    {
	c <<= 1;

	if ( !stuff_inhib )
	{
	    bit = buf & mask;

	    if ( state == 0 )
	    {
	        if ( bit )
		{
		    state = 1;
		    ones_cnt = 1;
		}
	    }

	    else
	    {
		if ( bit )
		{
		    ones_cnt++;

		    if ( ones_cnt == sync_ones )
		    {
			mask >>= 1;

			if ( mask == 0 )
			    fill_buffer( fea2kb_rec, ih, ifp, debug, dfp, &buf, &mask );

			(*stf)++;
			ones_cnt++;

			if ( debug >= 3 )
			{
			    Fprintf( dfp, "\t\t>>Stuffed bit @ 0x%lx:", mask );
			    Fprintf( dfp, " Buffer = 0x%lx\n", buf );
			}
		    }
		}

		else
		    state = 0;
	    }
	}

	else
	    state = 0;

	if ( buf & mask )
	    c |= 1;

	if ( debug >= 3 )
	    Fprintf( dfp, "\t\tField = 0x%x; Mask = 0x%x\n", c, mask );

	mask >>= 1;

	if ( mask == 0 )
	    fill_buffer( fea2kb_rec, ih, ifp, debug, dfp, &buf, &mask );
    }

    *field = c;
}

/*
 ********************************************************************************
 *  Subroutine to fill the bitstream buffer from input file.
 ********************************************************************************
 */

fill_buffer( fea2kb_rec, ih, ifp, debug, dfp, buf, mask )

FILE *dfp, *ifp;
int debug;
struct fea2kb *fea2kb_rec;
struct header *ih;
unsigned long *buf, *mask;
{
    static int tot;		/* Total bits input from bitstream */

    unsigned long err;		/* Error mask */

    if ( get_fea2kb_rec( fea2kb_rec, ih, ifp ) == EOF )
        Fprintf( stderr, "End of input file\n" );

    *buf = *fea2kb_rec->bitstream;
    err = *fea2kb_rec->error_mask;

    tot += 8*sizeof(long);

    if ( debug >= 4 )
    {
	Fprintf( dfp, "\t\t\tBitstream input = 0x%lx; Cumulative total = %d\n", *buf, tot );

	if ( err )
	    Fprintf( dfp, "\t\t\tError mask = 0x%lx; Corrupted input = 0x%lx\n",
	        err, *buf ^ err );
    }

    *buf ^= err;

    *mask = 0x80000000;
}