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78 lines
1.8 KiB
78 lines
1.8 KiB
24 years ago
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/*
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* bitstream.c
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*
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* Copyright (C) Aaron Holtzman - Dec 1999
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*
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* This file is part of ac3dec, a free AC-3 audio decoder
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*
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* ac3dec 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, or (at your option)
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* any later version.
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*
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* ac3dec 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 GNU Make; see the file COPYING. If not, write to
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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*/
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#include <inttypes.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include "ac3.h"
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#include "ac3_internal.h"
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#include "bitstream.h"
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#define BUFFER_SIZE 4096
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static uint8_t *buffer_start;
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uint32_t bits_left;
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uint32_t current_word;
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void bitstream_set_ptr (uint8_t * buf)
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{
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buffer_start = buf;
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bits_left = 0;
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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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current_word = *((uint32_t*)buffer_start)++;
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current_word = swab32(current_word);
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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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bitstream_get_bh(uint32_t num_bits)
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{
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uint32_t result;
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num_bits -= bits_left;
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result = (current_word << (32 - bits_left)) >> (32 - 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) | (current_word >> (32 - num_bits));
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bits_left = 32 - num_bits;
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return result;
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}
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