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133 lines
2.8 KiB
C
133 lines
2.8 KiB
C
/*
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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 <stdlib.h>
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#include <stdio.h>
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#include <string.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 uint_8 buffer[BUFFER_SIZE];
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static uint_32 *buffer_start, *buffer_end;
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static uint_8 *chunk_start, *chunk_end;
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uint_32 bits_left;
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uint_32 current_word;
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ssize_t (*bitstream_fill_buffer)(uint_8**,uint_8**);
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int bitstream_get_byte(void)
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{
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if(chunk_start == chunk_end)
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if (bitstream_fill_buffer(&chunk_start,&chunk_end) <= 0)
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return EOF;
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return (*chunk_start++);
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}
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uint_8 *bitstream_get_buffer_start(void)
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{
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return (uint_8 *) buffer_start;
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}
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int
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bitstream_buffer_frame(uint_32 frame_size)
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{
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uint_32 bytes_read;
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uint_32 num_bytes;
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bytes_read = 0;
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do
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{
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if(chunk_start > chunk_end)
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printf("argh!\n");
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if(chunk_start == chunk_end)
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if (bitstream_fill_buffer(&chunk_start,&chunk_end) <= 0)
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return EOF;
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num_bytes = chunk_end - chunk_start;
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if(bytes_read + num_bytes > frame_size)
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num_bytes = frame_size - bytes_read;
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memcpy(&buffer[bytes_read], chunk_start, num_bytes);
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bytes_read += num_bytes;
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chunk_start += num_bytes;
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}
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while (bytes_read != frame_size);
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buffer_start = (uint_32 *) buffer;
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buffer_end = (uint_32 *) (buffer + frame_size);
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bits_left = 0;
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return 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 = *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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uint_32
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bitstream_get_bh(uint_32 num_bits)
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{
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uint_32 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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void
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bitstream_init(ssize_t(*fill_function)(uint_8**,uint_8**))
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{
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// Setup the buffer fill callback
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bitstream_fill_buffer = fill_function;
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}
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