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