include/vlc_bits.h

   1 /*****************************************************************************
   2  * bits.h : Bit handling helpers
   3  *****************************************************************************
   4  * Copyright (C) 2003 the VideoLAN team
   5  * $Id$
   6  *
   7  * Authors: Laurent Aimar <fenrir@via.ecp.fr>
   8  *
   9  * This program 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  * This program 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., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  22  *****************************************************************************/
  23
  24 #ifndef VLC_BITS_H
  25 #define VLC_BITS_H 1
  26
  27 /**
  28  * \file
  29  * This file defines functions, structures for handling streams of bits in vlc
  30  */
  31
  32 typedef struct bs_s
  33 {
  34     uint8_t *p_start;
  35     uint8_t *p;
  36     uint8_t *p_end;
  37
  38     ssize_t  i_left;    /* i_count number of available bits */
  39 } bs_t;
  40
  41 static inline void bs_init( bs_t *s, const void *p_data, size_t i_data )
  42 {
  43     s->p_start = (void *)p_data;
  44     s->p       = s->p_start;
  45     s->p_end   = s->p_start + i_data;
  46     s->i_left  = 8;
  47 }
  48
  49 static inline int bs_pos( const bs_t *s )
  50 {
  51     return( 8 * ( s->p - s->p_start ) + 8 - s->i_left );
  52 }
  53
  54 static inline int bs_eof( const bs_t *s )
  55 {
  56     return( s->p >= s->p_end ? 1: 0 );
  57 }
  58
  59 static inline uint32_t bs_read( bs_t *s, int i_count )
  60 {
  61      static const uint32_t i_mask[33] =
  62      {  0x00,
  63         0x01,      0x03,      0x07,      0x0f,
  64         0x1f,      0x3f,      0x7f,      0xff,
  65         0x1ff,     0x3ff,     0x7ff,     0xfff,
  66         0x1fff,    0x3fff,    0x7fff,    0xffff,
  67         0x1ffff,   0x3ffff,   0x7ffff,   0xfffff,
  68         0x1fffff,  0x3fffff,  0x7fffff,  0xffffff,
  69         0x1ffffff, 0x3ffffff, 0x7ffffff, 0xfffffff,
  70         0x1fffffff,0x3fffffff,0x7fffffff,0xffffffff};
  71     int      i_shr;
  72     uint32_t i_result = 0;
  73
  74     while( i_count > 0 )
  75     {
  76         if( s->p >= s->p_end )
  77         {
  78             break;
  79         }
  80
  81         if( ( i_shr = s->i_left - i_count ) >= 0 )
  82         {
  83             /* more in the buffer than requested */
  84             i_result |= ( *s->p >> i_shr )&i_mask[i_count];
  85             s->i_left -= i_count;
  86             if( s->i_left == 0 )
  87             {
  88                 s->p++;
  89                 s->i_left = 8;
  90             }
  91             return( i_result );
  92         }
  93         else
  94         {
  95             /* less in the buffer than requested */
  96            i_result |= (*s->p&i_mask[s->i_left]) << -i_shr;
  97            i_count  -= s->i_left;
  98            s->p++;
  99            s->i_left = 8;
 100         }
 101     }
 102
 103     return( i_result );
 104 }
 105
 106 static inline uint32_t bs_read1( bs_t *s )
 107 {
 108     if( s->p < s->p_end )
 109     {
 110         unsigned int i_result;
 111
 112         s->i_left--;
 113         i_result = ( *s->p >> s->i_left )&0x01;
 114         if( s->i_left == 0 )
 115         {
 116             s->p++;
 117             s->i_left = 8;
 118         }
 119         return i_result;
 120     }
 121
 122     return 0;
 123 }
 124
 125 static inline uint32_t bs_show( bs_t *s, int i_count )
 126 {
 127     bs_t     s_tmp = *s;
 128     return bs_read( &s_tmp, i_count );
 129 }
 130
 131 static inline void bs_skip( bs_t *s, ssize_t i_count )
 132 {
 133     s->i_left -= i_count;
 134
 135     if( s->i_left <= 0 )
 136     {
 137         const int i_bytes = ( -s->i_left + 8 ) / 8;
 138
 139         s->p += i_bytes;
 140         s->i_left += 8 * i_bytes;
 141     }
 142 }
 143
 144 static inline void bs_write( bs_t *s, int i_count, uint32_t i_bits )
 145 {
 146     while( i_count > 0 )
 147     {
 148         if( s->p >= s->p_end )
 149         {
 150             break;
 151         }
 152
 153         i_count--;
 154
 155         if( ( i_bits >> i_count )&0x01 )
 156         {
 157             *s->p |= 1 << ( s->i_left - 1 );
 158         }
 159         else
 160         {
 161             *s->p &= ~( 1 << ( s->i_left - 1 ) );
 162         }
 163         s->i_left--;
 164         if( s->i_left == 0 )
 165         {
 166             s->p++;
 167             s->i_left = 8;
 168         }
 169     }
 170 }
 171
 172 static inline void bs_align( bs_t *s )
 173 {
 174     if( s->i_left != 8 )
 175     {
 176         s->i_left = 8;
 177         s->p++;
 178     }
 179 }
 180
 181 static inline void bs_align_0( bs_t *s )
 182 {
 183     if( s->i_left != 8 )
 184     {
 185         bs_write( s, s->i_left, 0 );
 186     }
 187 }
 188
 189 static inline void bs_align_1( bs_t *s )
 190 {
 191     while( s->i_left != 8 )
 192     {
 193         bs_write( s, 1, 1 );
 194     }
 195 }
 196
 197 #endif