include/vlc_bits.h

   1 /*****************************************************************************
   2  * vlc_bits.h : Bit handling helpers
   3  *****************************************************************************
   4  * Copyright (C) 2001, 2002, 2003, 2006, 2015 VLC authors and VideoLAN
   5  * $Id$
   6  *
   7  * Authors: Laurent Aimar <fenrir@via.ecp.fr>
   8  *          Gildas Bazin <gbazin at videolan dot org>
   9  *          Rafaël Carré <funman at videolan dot org>
  10  *
  11  * This program is free software; you can redistribute it and/or modify it
  12  * under the terms of the GNU Lesser General Public License as published by
  13  * the Free Software Foundation; either version 2.1 of the License, or
  14  * (at your option) any later version.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  19  * GNU Lesser General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU Lesser General Public License
  22  * along with this program; if not, write to the Free Software Foundation,
  23  * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  24  *****************************************************************************/
  25 #ifndef VLC_BITS_H
  26 #define VLC_BITS_H 1
  27
  28 #include <vlc_common.h>
  29
  30 /**
  31  * \file
  32  * This file defines functions, structures for handling streams of bits in vlc
  33  */
  34
  35 typedef struct bs_s
  36 {
  37     uint8_t *p_start;
  38     uint8_t *p;
  39     uint8_t *p_end;
  40
  41     ssize_t  i_left;    /* i_count number of available bits */
  42     bool     b_read_only;
  43
  44      /* forward read modifier (p_start, p_end, p_fwpriv, count) */
  45     uint8_t *(*pf_forward)(uint8_t *, uint8_t *, void *, size_t);
  46     void    *p_fwpriv;
  47 } bs_t;
  48
  49 static inline void bs_write_init( bs_t *s, void *p_data, size_t i_data )
  50 {
  51     s->p_start = (uint8_t *)p_data;
  52     s->p       = s->p_start;
  53     s->p_end   = s->p_start + i_data;
  54     s->i_left  = 8;
  55     s->b_read_only = false;
  56     s->p_fwpriv = NULL;
  57     s->pf_forward = NULL;
  58 }
  59
  60 static inline void bs_init( bs_t *s, const void *p_data, size_t i_data )
  61 {
  62     bs_write_init( s, (void*) p_data, i_data );
  63     s->b_read_only = true;
  64 }
  65
  66 static inline int bs_pos( const bs_t *s )
  67 {
  68     return( 8 * ( s->p - s->p_start ) + 8 - s->i_left );
  69 }
  70
  71 static inline int bs_remain( const bs_t *s )
  72 {
  73     if( s->p >= s->p_end )
  74         return 0;
  75     else
  76     return( 8 * ( s->p_end - s->p ) - 8 + s->i_left );
  77 }
  78
  79 static inline int bs_eof( const bs_t *s )
  80 {
  81     return( s->p >= s->p_end ? 1: 0 );
  82 }
  83
  84 #define bs_forward( s, i ) \
  85     s->p = s->pf_forward ? s->pf_forward( s->p, s->p_end, s->p_fwpriv, i ) : s->p + i
  86
  87 static inline uint32_t bs_read( bs_t *s, int i_count )
  88 {
  89      static const uint32_t i_mask[33] =
  90      {  0x00,
  91         0x01,      0x03,      0x07,      0x0f,
  92         0x1f,      0x3f,      0x7f,      0xff,
  93         0x1ff,     0x3ff,     0x7ff,     0xfff,
  94         0x1fff,    0x3fff,    0x7fff,    0xffff,
  95         0x1ffff,   0x3ffff,   0x7ffff,   0xfffff,
  96         0x1fffff,  0x3fffff,  0x7fffff,  0xffffff,
  97         0x1ffffff, 0x3ffffff, 0x7ffffff, 0xfffffff,
  98         0x1fffffff,0x3fffffff,0x7fffffff,0xffffffff};
  99     int      i_shr, i_drop = 0;
 100     uint32_t i_result = 0;
 101
 102     if( i_count > 32 )
 103     {
 104         i_drop = i_count - 32;
 105         i_count = 32;
 106     }
 107
 108     while( i_count > 0 )
 109     {
 110         if( s->p >= s->p_end )
 111         {
 112             break;
 113         }
 114
 115         if( ( i_shr = s->i_left - i_count ) >= 0 )
 116         {
 117             /* more in the buffer than requested */
 118             i_result |= ( *s->p >> i_shr )&i_mask[i_count];
 119             s->i_left -= i_count;
 120             if( s->i_left == 0 )
 121             {
 122                 bs_forward( s, 1 );
 123                 s->i_left = 8;
 124             }
 125             break;
 126         }
 127         else
 128         {
 129             /* less in the buffer than requested */
 130            if( -i_shr == 32 )
 131                i_result = 0;
 132            else
 133                i_result |= (*s->p&i_mask[s->i_left]) << -i_shr;
 134            i_count  -= s->i_left;
 135            bs_forward( s, 1);
 136            s->i_left = 8;
 137         }
 138     }
 139
 140     if( i_drop )
 141         bs_forward( s, i_drop );
 142
 143     return( i_result );
 144 }
 145
 146 static inline uint32_t bs_read1( bs_t *s )
 147 {
 148     if( s->p < s->p_end )
 149     {
 150         unsigned int i_result;
 151
 152         s->i_left--;
 153         i_result = ( *s->p >> s->i_left )&0x01;
 154         if( s->i_left == 0 )
 155         {
 156             bs_forward( s, 1 );
 157             s->i_left = 8;
 158         }
 159         return i_result;
 160     }
 161
 162     return 0;
 163 }
 164
 165 static inline uint32_t bs_show( bs_t *s, int i_count )
 166 {
 167     bs_t     s_tmp = *s;
 168     return bs_read( &s_tmp, i_count );
 169 }
 170
 171 static inline void bs_skip( bs_t *s, ssize_t i_count )
 172 {
 173     s->i_left -= i_count;
 174
 175     if( s->i_left <= 0 )
 176     {
 177         const size_t i_bytes = 1 + s->i_left / -8;
 178         bs_forward( s, i_bytes );
 179         if( i_bytes * 8 < i_bytes /* ofw */ )
 180             s->i_left = i_bytes;
 181         else
 182             s->i_left += 8 * i_bytes;
 183     }
 184 }
 185
 186 static inline void bs_write( bs_t *s, int i_count, uint32_t i_bits )
 187 {
 188     if( s->b_read_only )
 189         return;
 190
 191     while( i_count > 0 )
 192     {
 193         if( s->p >= s->p_end )
 194         {
 195             break;
 196         }
 197
 198         i_count--;
 199
 200         if( ( i_bits >> i_count )&0x01 )
 201         {
 202             *s->p |= 1 << ( s->i_left - 1 );
 203         }
 204         else
 205         {
 206             *s->p &= ~( 1 << ( s->i_left - 1 ) );
 207         }
 208         s->i_left--;
 209         if( s->i_left == 0 )
 210         {
 211             bs_forward( s, 1 );
 212             s->i_left = 8;
 213         }
 214     }
 215 }
 216
 217 static inline bool bs_aligned( bs_t *s )
 218 {
 219     return s->i_left % 8 == 0;
 220 }
 221
 222 static inline void bs_align( bs_t *s )
 223 {
 224     if( s->i_left != 8 )
 225     {
 226         s->i_left = 8;
 227         s->p++;
 228     }
 229 }
 230
 231 static inline void bs_align_0( bs_t *s )
 232 {
 233     if( s->i_left != 8 )
 234     {
 235         bs_write( s, s->i_left, 0 );
 236     }
 237 }
 238
 239 static inline void bs_align_1( bs_t *s )
 240 {
 241     while( !s->b_read_only && s->i_left != 8 )
 242     {
 243         bs_write( s, 1, 1 );
 244     }
 245 }
 246
 247 /* Read unsigned Exp-Golomb code */
 248 static inline uint_fast32_t bs_read_ue( bs_t * bs )
 249 {
 250     unsigned i = 0;
 251
 252     while( bs_read1( bs ) == 0 && bs->p < bs->p_end && i < 31 )
 253         i++;
 254
 255     return (1U << i) - 1 + bs_read( bs, i );
 256 }
 257
 258 /* Read signed Exp-Golomb code */
 259 static inline int_fast32_t bs_read_se( bs_t *s )
 260 {
 261     uint_fast32_t val = bs_read_ue( s );
 262
 263     return (val & 0x01) ? (int_fast32_t)((val + 1) / 2)
 264                         : -(int_fast32_t)(val / 2);
 265 }
 266
 267 #undef bs_forward
 268
 269 #endif