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# bitstream.c

    00001 /*
    00002  * bitstream.c
    00003  * Copyright (C) 2000-2002 Michel Lespinasse <walken@zoy.org>
    00004  * Copyright (C) 1999-2000 Aaron Holtzman <aholtzma@ess.engr.uvic.ca>
    00005  *
    00006  * This file is part of a52dec, a free ATSC A-52 stream decoder.
    00007  * See http://liba52.sourceforge.net/ for updates.
    00008  *
    00009  * a52dec is free software; you can redistribute it and/or modify
    00010  * it under the terms of the GNU General Public License as published by
    00011  * the Free Software Foundation; either version 2 of the License, or
    00012  * (at your option) any later version.
    00013  *
    00014  * a52dec is distributed in the hope that it will be useful,
    00015  * but WITHOUT ANY WARRANTY; without even the implied warranty of
    00016  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    00017  * GNU General Public License for more details.
    00018  *
    00019  * You should have received a copy of the GNU General Public License
    00020  * along with this program; if not, write to the Free Software
    00021  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    00022  */
    00023
    00024 #include "config.h"
    00025
    00026 #include <inttypes.h>
    00027
    00028 #include "a52.h"
    00029 #include "a52_internal.h"
    00030 #include "bitstream.h"
    00031
    00032 #define BUFFER_SIZE 4096
    00033
    00034 void a52_bitstream_set_ptr (a52_state_t * state, uint8_t * buf)
    00035 {
    00036     int align;
    00037
    00038     align = (long)buf & 3;
    00039     state->buffer_start = (uint32_t *) (buf - align);
    00040     state->bits_left = 0;
    00041     bitstream_get (state, align * 8);
    00042 }
    00043
    00044 static inline void bitstream_fill_current (a52_state_t * state)
    00045 {
    00046     uint32_t tmp;
    00047
    00048     tmp = *(state->buffer_start++);
    00049     state->current_word = swab32 (tmp);
    00050 }
    00051
    00052 /*
    00053  * The fast paths for _get is in the
    00054  * bitstream.h header file so it can be inlined.
    00055  *
    00056  * The "bottom half" of this routine is suffixed _bh
    00057  *
    00058  * -ah
    00059  */
    00060
    00061 uint32_t a52_bitstream_get_bh (a52_state_t * state, uint32_t num_bits)
    00062 {
    00063     uint32_t result;
    00064
    00065     num_bits -= state->bits_left;
    00066     result = ((state->current_word << (32 - state->bits_left)) >>
    00067               (32 - state->bits_left));
    00068
    00069     bitstream_fill_current (state);
    00070
    00071     if (num_bits != 0)
    00072         result = (result << num_bits) | (state->current_word >> (32 - num_bits));
    00073
    00074     state->bits_left = 32 - num_bits;
    00075
    00076     return result;
    00077 }
    00078
    00079 int32_t a52_bitstream_get_bh_2 (a52_state_t * state, uint32_t num_bits)
    00080 {
    00081     int32_t result;
    00082
    00083     num_bits -= state->bits_left;
    00084     result = ((((int32_t)state->current_word) << (32 - state->bits_left)) >>
    00085               (32 - state->bits_left));
    00086
    00087     bitstream_fill_current(state);
    00088
    00089     if (num_bits != 0)
    00090         result = (result << num_bits) | (state->current_word >> (32 - num_bits));
    00091
    00092     state->bits_left = 32 - num_bits;
    00093
    00094     return result;
    00095 }