?? bitstream.c
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/* * bitstream.c * * Copyright (C) Aaron Holtzman - May 1999 * * This file is part of ac3dec, a free Dolby AC-3 stream decoder. * * ac3dec 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, or (at your option) * any later version. * * ac3dec 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 GNU Make; see the file COPYING. If not, write to * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. * */#include <stdlib.h>#include <stdio.h>#include "ac3.h"#include "decode.h"#include "crc.h"#include "bitstream.h"//My vego-matic endian swapping routine#define SWAP_ENDIAN32(x) ((((uint_8*)&x)[0] << 24) | \ (((uint_8*)&x)[1] << 16) | \ (((uint_8*)&x)[2] << 8) | \ ((uint_8*)&x)[3]) static void bitstream_load(bitstream_t *bs);/* Fetches 1-32 bits from the file opened in bitstream_open */uint_32bitstream_get(bitstream_t *bs,uint_32 num_bits){ uint_32 result; uint_32 bits_read; uint_32 bits_to_go; if(num_bits == 0) return 0;#ifdef DO_NIST result = inputstream->get_bits(num_bits);#else bits_read = num_bits > bs->bits_left ? bs->bits_left : num_bits; result = bs->current_word >> (32 - bits_read); bs->current_word <<= bits_read; bs->bits_left -= bits_read; if(bs->bits_left == 0) bitstream_load(bs); if (bits_read < num_bits) { bits_to_go = num_bits - bits_read; result <<= bits_to_go; result |= bs->current_word >> (32 - bits_to_go); bs->current_word <<= bits_to_go; bs->bits_left -= bits_to_go; } bs->total_bits_read += num_bits;#endif crc_process(result,num_bits); return result;}#ifndef DO_NISTstatic voidbitstream_load(bitstream_t *bs){ int bytes_read; bytes_read = fread(&bs->current_word,1,4,bs->file); bs->current_word = SWAP_ENDIAN32(bs->current_word); bs->bits_left = bytes_read * 8; //FIXME finishing up the stream isn't done too gracefully if (bytes_read < 4) bs->done = 1;}/* Opens a bitstream for use in bitstream_get */bitstream_t*bitstream_open(FILE *file){ bitstream_t *bs; if(!file) return 0; bs = malloc(sizeof(bitstream_t)); if(!bs) return 0; bs->done = 0; /* Read in the first 32 bit word and initialize the structure */ bs->file = file; bitstream_load(bs); return bs;}int bitstream_done(bitstream_t *bs){ return (bs->done);}void bitstream_close(bitstream_t *bs){ if(bs->file) fclose(bs->file); free(bs);}#endif
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