www.pudn.com > mediator15src.zip > bitstream.c

/* 
 * bitstream.c 
 * Copyright (C) 2000-2002 Michel Lespinasse  
 * Copyright (C) 1999-2000 Aaron Holtzman  
 * 
 * This file is part of a52dec, a free ATSC A-52 stream decoder. 
 * See http://liba52.sourceforge.net/ for updates. 
 * 
 * a52dec is free software; you can redistribute it and/or modify 
 * it under the terms of the GNU General Public License as published by 
 * the Free Software Foundation; either version 2 of the License, or 
 * (at your option) any later version. 
 * 
 * a52dec is distributed in the hope that it will be useful, 
 * but WITHOUT ANY WARRANTY; without even the implied warranty of 
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
 * GNU General Public License for more details. 
 * 
 * You should have received a copy of the GNU General Public License 
 * along with this program; if not, write to the Free Software 
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 
 */ 
 
#include "config.h" 
 
#include "a52.h" 
#include "a52_internal.h" 
#include "bitstream.h" 
 
#define BUFFER_SIZE 4096 
 
static uint32_t * buffer_start; 
 
uint32_t a52_bits_left; 
uint32_t a52_current_word; 
 
void a52_bitstream_set_ptr (uint8_t * buf) 
{ 
    int align; 
 
    align = (long)buf & 3; 
    buffer_start = (uint32_t *) (buf - align); 
    a52_bits_left = 0; 
    bitstream_get (align * 8); 
} 
 
__inline static void 
bitstream_fill_current() 
{ 
    uint32_t tmp; 
 
    tmp = *(buffer_start++); 
    a52_current_word = swab32 (tmp); 
} 
 
/* 
 * The fast paths for _get is in the 
 * bitstream.h header file so it can be inlined. 
 * 
 * The "bottom half" of this routine is suffixed _bh 
 * 
 * -ah 
 */ 
 
uint32_t 
a52_bitstream_get_bh(uint32_t num_bits) 
{ 
    uint32_t result; 
 
    num_bits -= a52_bits_left; 
    result = ((a52_current_word << (32 - a52_bits_left)) >> 
	      (32 - a52_bits_left)); 
 
    bitstream_fill_current(); 
 
    if(num_bits != 0) 
	result = (result << num_bits) | (a52_current_word >> (32 - num_bits)); 
 
    a52_bits_left = 32 - num_bits; 
 
    return result; 
} 
 
int32_t 
a52_bitstream_get_bh_2(uint32_t num_bits) 
{ 
    int32_t result; 
 
    num_bits -= a52_bits_left; 
    result = ((((int32_t)a52_current_word) << (32 - a52_bits_left)) >> 
	      (32 - a52_bits_left)); 
 
    bitstream_fill_current(); 
 
    if(num_bits != 0) 
	result = (result << num_bits) | (a52_current_word >> (32 - num_bits)); 
	 
    a52_bits_left = 32 - num_bits; 
 
    return result; 
}