apps/codecs/liba52/bitstream.c

   1 /*
   2  * bitstream.c
   3  * Copyright (C) 2000-2003 Michel Lespinasse <walken@zoy.org>
   4  * Copyright (C) 1999-2000 Aaron Holtzman <aholtzma@ess.engr.uvic.ca>
   5  *
   6  * This file is part of a52dec, a free ATSC A-52 stream decoder.
   7  * See http://liba52.sourceforge.net/ for updates.
   8  *
   9  * a52dec is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License as published by
  11  * the Free Software Foundation; either version 2 of the License, or
  12  * (at your option) any later version.
  13  *
  14  * a52dec is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU General Public License
  20  * along with this program; if not, write to the Free Software
  21  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  22  */
  23
  24 #include "config-a52.h"
  25
  26 #include <inttypes.h>
  27
  28 #include "a52.h"
  29 #include "a52_internal.h"
  30 #include "bitstream.h"
  31
  32 #define BUFFER_SIZE 4096
  33
  34 void a52_bitstream_set_ptr (a52_state_t * state, uint8_t * buf)
  35 {
  36     int align;
  37
  38     align = (long)buf & 3;
  39     state->buffer_start = (uint32_t *) (buf - align);
  40     state->bits_left = 0;
  41     state->current_word = 0;
  42     bitstream_get (state, align * 8);
  43     bitstream_get_2 (state, 0); /* pretend function is used - keep gcc happy */
  44 }
  45
  46 static inline void bitstream_fill_current (a52_state_t * state)
  47 {
  48     uint32_t tmp;
  49
  50     tmp = *(state->buffer_start++);
  51     state->current_word = swab32 (tmp);
  52 }
  53
  54 /*
  55  * The fast paths for _get is in the
  56  * bitstream.h header file so it can be inlined.
  57  *
  58  * The "bottom half" of this routine is suffixed _bh
  59  *
  60  * -ah
  61  */
  62
  63 uint32_t a52_bitstream_get_bh (a52_state_t * state, uint32_t num_bits)
  64 {
  65     uint32_t result;
  66
  67     num_bits -= state->bits_left;
  68     result = ((state->current_word << (32 - state->bits_left)) >>
  69               (32 - state->bits_left));
  70
  71     bitstream_fill_current (state);
  72
  73     if (num_bits != 0)
  74         result = (result << num_bits) | (state->current_word >> (32 - num_bits));
  75
  76     state->bits_left = 32 - num_bits;
  77
  78     return result;
  79 }
  80
  81 int32_t a52_bitstream_get_bh_2 (a52_state_t * state, uint32_t num_bits)
  82 {
  83     int32_t result;
  84
  85     num_bits -= state->bits_left;
  86     result = ((((int32_t)state->current_word) << (32 - state->bits_left)) >>
  87               (32 - state->bits_left));
  88
  89     bitstream_fill_current(state);
  90
  91     if (num_bits != 0)
  92         result = (result << num_bits) | (state->current_word >> (32 - num_bits));
  93
  94     state->bits_left = 32 - num_bits;
  95
  96     return result;
  97 }