mirror of
https://code.videolan.org/videolan/vlc
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304 lines
6.9 KiB
C
304 lines
6.9 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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*
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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 bs_t;
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typedef struct
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{
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/* forward read modifier (p_start, p_end, p_fwpriv, count, pos) */
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size_t (*pf_byte_forward)(bs_t *, size_t);
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size_t (*pf_byte_pos)(const bs_t *);
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} bs_byte_callbacks_t;
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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; /* points to currently read/written byte */
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uint8_t *p_end;
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uint8_t i_left; /* i_count number of available bits */
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bool b_read_only;
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bool b_error;
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bs_byte_callbacks_t cb;
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void *p_priv;
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} bs_t;
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static size_t bs_impl_bytes_forward( bs_t *s, size_t i_count )
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{
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if( s->p == NULL )
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{
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s->p = s->p_start;
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return 1;
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}
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if( s->p >= s->p_end )
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return 0;
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if( (size_t) (s->p_end - s->p) < i_count )
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i_count = s->p_end - s->p;
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s->p += i_count;
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return i_count;
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}
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static size_t bs_impl_bytes_pos( const bs_t *s )
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{
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if( s->p )
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return s->p < s->p_end ? s->p - s->p_start + 1 : s->p - s->p_start;
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else
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return 0;
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}
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static inline void bs_init_custom( bs_t *s, const void *p_data, size_t i_data,
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const bs_byte_callbacks_t *cb, void *priv )
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{
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s->p_start = (uint8_t *)p_data;
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s->p = NULL;
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s->p_end = s->p_start + i_data;
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s->i_left = 0;
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s->b_read_only = true;
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s->b_error = false;
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s->p_priv = priv;
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s->cb = *cb;
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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_byte_callbacks_t cb = {
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bs_impl_bytes_forward,
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bs_impl_bytes_pos,
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};
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bs_init_custom( s, p_data, i_data, &cb, NULL );
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}
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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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bs_init( s, (const void *) p_data, i_data );
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s->b_read_only = false;
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}
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static inline int bs_refill( bs_t *s )
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{
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if( s->i_left == 0 )
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{
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if( s->cb.pf_byte_forward( s, 1 ) != 1 )
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return -1;
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if( s->p < s->p_end )
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s->i_left = 8;
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}
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return s->i_left > 0 ? 0 : 1;
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}
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static inline bool bs_error( const bs_t *s )
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{
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return s->b_error;
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}
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static inline bool bs_eof( bs_t *s )
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{
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return bs_refill( s ) != 0;
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}
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static inline size_t bs_pos( const bs_t *s )
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{
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return 8 * s->cb.pf_byte_pos( s ) - s->i_left;
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}
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static inline void bs_skip( bs_t *s, size_t i_count )
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{
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if( i_count == 0 )
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return;
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if( bs_refill( s ) )
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{
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s->b_error = true;
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return;
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}
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if( i_count > s->i_left )
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{
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i_count -= s->i_left;
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s->i_left = 0;
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size_t bytes = i_count / 8;
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if( bytes && s->cb.pf_byte_forward( s, bytes ) != bytes )
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{
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s->b_error = true;
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return;
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}
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i_count = i_count % 8;
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if( i_count > 0 )
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{
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if( !bs_refill( s ) )
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s->i_left = 8 - i_count;
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else
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s->b_error = true;
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}
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}
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else s->i_left -= i_count;
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}
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static inline uint32_t bs_read( bs_t *s, uint8_t i_count )
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{
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uint8_t i_shr, i_drop = 0;
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uint32_t i_result = 0;
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if( i_count > 32 )
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{
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i_drop = i_count - 32;
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i_count = 32;
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}
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while( i_count > 0 )
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{
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if( bs_refill( s ) )
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{
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s->b_error = true;
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break;
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}
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if( s->i_left > i_count )
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{
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uint_fast32_t mask = (UINT64_C(1) << i_count) - 1;
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i_shr = s->i_left - i_count;
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/* more in the buffer than requested */
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i_result |= ( *s->p >> i_shr ) & mask;
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s->i_left -= i_count;
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break;
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}
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else
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{
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uint_fast32_t mask = (UINT64_C(1) << s->i_left) - 1;
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i_shr = i_count - s->i_left;
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/* less in the buffer than requested */
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if( i_shr >= 32 )
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i_result = 0;
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else
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i_result |= (*s->p & mask) << i_shr;
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i_count -= s->i_left;
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s->i_left = 0;
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}
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}
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if( i_drop )
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bs_skip( s, i_drop );
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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( bs_refill( s ) )
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{
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s->b_error = true;
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return 0;
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}
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s->i_left--;
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return ( *s->p >> s->i_left )&0x01;
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}
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static inline void bs_write( bs_t *s, uint8_t 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( bs_refill( s ) )
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{
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s->b_error = true;
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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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}
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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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s->i_left = 0;
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}
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static inline void bs_write_align( bs_t *s, uint8_t v )
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{
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if( !s->b_read_only && (s->i_left % 8) )
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bs_write( s, s->i_left, v ? 0xFF : 0 );
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}
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#define bs_align_0( s ) bs_write_align( s, 0 )
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#define bs_align_1( s ) bs_write_align( s, 1 )
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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->b_error &&
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bs_read1( bs ) == 0 &&
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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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