mirror of https://code.videolan.org/videolan/vlc
258 lines
6.1 KiB
C
258 lines
6.1 KiB
C
/*****************************************************************************
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* vlc_bits.h : Bit handling helpers
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*****************************************************************************
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* Copyright (C) 2001, 2002, 2003, 2006, 2015 VLC authors and VideoLAN
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* $Id$
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*
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* Authors: Laurent Aimar <fenrir@via.ecp.fr>
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* Gildas Bazin <gbazin at videolan dot org>
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* Rafaël Carré <funman at videolan dot org>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation; either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
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*****************************************************************************/
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#ifndef VLC_BITS_H
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#define VLC_BITS_H 1
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#include <vlc_common.h>
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/**
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* \file
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* This file defines functions, structures for handling streams of bits in vlc
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*/
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typedef struct bs_s
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{
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uint8_t *p_start;
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uint8_t *p;
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uint8_t *p_end;
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ssize_t i_left; /* i_count number of available bits */
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bool b_read_only;
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/* forward read modifier (p_start, p_end, p_fwpriv, count) */
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uint8_t *(*pf_forward)(uint8_t *, uint8_t *, void *, size_t);
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void *p_fwpriv;
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} bs_t;
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static inline void bs_write_init( bs_t *s, void *p_data, size_t i_data )
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{
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s->p_start = (uint8_t *)p_data;
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s->p = s->p_start;
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s->p_end = s->p_start + i_data;
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s->i_left = 8;
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s->b_read_only = false;
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s->p_fwpriv = NULL;
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s->pf_forward = NULL;
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}
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static inline void bs_init( bs_t *s, const void *p_data, size_t i_data )
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{
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bs_write_init( s, (void*) p_data, i_data );
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s->b_read_only = true;
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}
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static inline int bs_pos( const bs_t *s )
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{
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return( 8 * ( s->p - s->p_start ) + 8 - s->i_left );
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}
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static inline int bs_remain( const bs_t *s )
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{
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if( s->p >= s->p_end )
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return 0;
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else
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return( 8 * ( s->p_end - s->p ) - 8 + s->i_left );
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}
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static inline int bs_eof( const bs_t *s )
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{
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return( s->p >= s->p_end ? 1: 0 );
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}
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#define bs_forward( s, i ) \
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s->p = s->pf_forward ? s->pf_forward( s->p, s->p_end, s->p_fwpriv, i ) : s->p + i
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static inline uint32_t bs_read( bs_t *s, int i_count )
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{
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static const uint32_t i_mask[33] =
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{ 0x00,
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0x01, 0x03, 0x07, 0x0f,
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0x1f, 0x3f, 0x7f, 0xff,
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0x1ff, 0x3ff, 0x7ff, 0xfff,
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0x1fff, 0x3fff, 0x7fff, 0xffff,
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0x1ffff, 0x3ffff, 0x7ffff, 0xfffff,
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0x1fffff, 0x3fffff, 0x7fffff, 0xffffff,
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0x1ffffff, 0x3ffffff, 0x7ffffff, 0xfffffff,
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0x1fffffff,0x3fffffff,0x7fffffff,0xffffffff};
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int i_shr;
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uint32_t i_result = 0;
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while( i_count > 0 )
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{
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if( s->p >= s->p_end )
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{
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break;
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}
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if( ( i_shr = s->i_left - i_count ) >= 0 )
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{
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/* more in the buffer than requested */
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i_result |= ( *s->p >> i_shr )&i_mask[i_count];
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s->i_left -= i_count;
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if( s->i_left == 0 )
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{
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bs_forward( s, 1 );
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s->i_left = 8;
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}
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return( i_result );
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}
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else
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{
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/* less in the buffer than requested */
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i_result |= (*s->p&i_mask[s->i_left]) << -i_shr;
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i_count -= s->i_left;
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bs_forward( s, 1);
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s->i_left = 8;
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}
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}
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return( i_result );
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}
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static inline uint32_t bs_read1( bs_t *s )
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{
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if( s->p < s->p_end )
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{
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unsigned int i_result;
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s->i_left--;
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i_result = ( *s->p >> s->i_left )&0x01;
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if( s->i_left == 0 )
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{
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bs_forward( s, 1 );
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s->i_left = 8;
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}
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return i_result;
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}
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return 0;
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}
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static inline uint32_t bs_show( bs_t *s, int i_count )
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{
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bs_t s_tmp = *s;
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return bs_read( &s_tmp, i_count );
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}
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static inline void bs_skip( bs_t *s, ssize_t i_count )
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{
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s->i_left -= i_count;
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if( s->i_left <= 0 )
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{
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const size_t i_bytes = 1 + s->i_left / -8;
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bs_forward( s, i_bytes );
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if( i_bytes * 8 < i_bytes /* ofw */ )
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s->i_left = i_bytes;
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else
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s->i_left += 8 * i_bytes;
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}
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}
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static inline void bs_write( bs_t *s, int i_count, uint32_t i_bits )
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{
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if( s->b_read_only )
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return;
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while( i_count > 0 )
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{
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if( s->p >= s->p_end )
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{
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break;
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}
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i_count--;
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if( ( i_bits >> i_count )&0x01 )
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{
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*s->p |= 1 << ( s->i_left - 1 );
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}
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else
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{
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*s->p &= ~( 1 << ( s->i_left - 1 ) );
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}
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s->i_left--;
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if( s->i_left == 0 )
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{
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bs_forward( s, 1 );
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s->i_left = 8;
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}
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}
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}
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static inline bool bs_aligned( bs_t *s )
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{
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return s->i_left % 8 == 0;
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}
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static inline void bs_align( bs_t *s )
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{
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if( s->i_left != 8 )
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{
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s->i_left = 8;
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s->p++;
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}
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}
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static inline void bs_align_0( bs_t *s )
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{
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if( s->i_left != 8 )
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{
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bs_write( s, s->i_left, 0 );
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}
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}
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static inline void bs_align_1( bs_t *s )
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{
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while( !s->b_read_only && s->i_left != 8 )
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{
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bs_write( s, 1, 1 );
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}
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}
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/* Read unsigned Exp-Golomb code */
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static inline uint_fast32_t bs_read_ue( bs_t * bs )
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{
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unsigned i = 0;
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while( bs_read1( bs ) == 0 && bs->p < bs->p_end && i < 31 )
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i++;
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return (1U << i) - 1 + bs_read( bs, i );
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}
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/* Read signed Exp-Golomb code */
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static inline int_fast32_t bs_read_se( bs_t *s )
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{
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uint_fast32_t val = bs_read_ue( s );
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return (val & 0x01) ? (int_fast32_t)((val + 1) / 2)
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: -(int_fast32_t)(val / 2);
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}
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#undef bs_forward
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#endif
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