/***************************************************************************** * vlc_bits.h : Bit handling helpers ***************************************************************************** * Copyright (C) 2001, 2002, 2003, 2006, 2015 VLC authors and VideoLAN * * Authors: Laurent Aimar * Gildas Bazin * Rafaël Carré * * This program is free software; you can redistribute it and/or modify it * under the terms of the GNU Lesser General Public License as published by * the Free Software Foundation; either version 2.1 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public License * along with this program; if not, write to the Free Software Foundation, * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA. *****************************************************************************/ #ifndef VLC_BITS_H #define VLC_BITS_H 1 #include /** * \file * This file defines functions, structures for handling streams of bits in vlc */ typedef struct bs_s bs_t; typedef struct { /* forward read modifier (p_start, p_end, p_fwpriv, count, pos) */ size_t (*pf_byte_forward)(bs_t *, size_t); size_t (*pf_byte_pos)(const bs_t *); } bs_byte_callbacks_t; typedef struct bs_s { uint8_t *p_start; uint8_t *p; /* points to currently read/written byte */ uint8_t *p_end; uint8_t i_left; /* i_count number of available bits */ bool b_read_only; bool b_error; bs_byte_callbacks_t cb; void *p_priv; } bs_t; static size_t bs_impl_bytes_forward( bs_t *s, size_t i_count ) { if( s->p == NULL ) { s->p = s->p_start; return 1; } if( s->p >= s->p_end ) return 0; if( (size_t) (s->p_end - s->p) < i_count ) i_count = s->p_end - s->p; s->p += i_count; return i_count; } static size_t bs_impl_bytes_pos( const bs_t *s ) { if( s->p ) return s->p < s->p_end ? s->p - s->p_start + 1 : s->p - s->p_start; else return 0; } static inline void bs_init_custom( bs_t *s, const void *p_data, size_t i_data, const bs_byte_callbacks_t *cb, void *priv ) { s->p_start = (uint8_t *)p_data; s->p = NULL; s->p_end = s->p_start + i_data; s->i_left = 0; s->b_read_only = true; s->b_error = false; s->p_priv = priv; s->cb = *cb; } static inline void bs_init( bs_t *s, const void *p_data, size_t i_data ) { bs_byte_callbacks_t cb = { bs_impl_bytes_forward, bs_impl_bytes_pos, }; bs_init_custom( s, p_data, i_data, &cb, NULL ); } static inline void bs_write_init( bs_t *s, void *p_data, size_t i_data ) { bs_init( s, (const void *) p_data, i_data ); s->b_read_only = false; } static inline int bs_refill( bs_t *s ) { if( s->i_left == 0 ) { if( s->cb.pf_byte_forward( s, 1 ) != 1 ) return -1; if( s->p < s->p_end ) s->i_left = 8; } return s->i_left > 0 ? 0 : 1; } static inline bool bs_error( const bs_t *s ) { return s->b_error; } static inline bool bs_eof( bs_t *s ) { return bs_refill( s ) != 0; } static inline size_t bs_pos( const bs_t *s ) { return 8 * s->cb.pf_byte_pos( s ) - s->i_left; } static inline void bs_skip( bs_t *s, size_t i_count ) { if( i_count == 0 ) return; if( bs_refill( s ) ) { s->b_error = true; return; } if( i_count > s->i_left ) { i_count -= s->i_left; s->i_left = 0; size_t bytes = i_count / 8; if( bytes && s->cb.pf_byte_forward( s, bytes ) != bytes ) { s->b_error = true; return; } i_count = i_count % 8; if( i_count > 0 ) { if( !bs_refill( s ) ) s->i_left = 8 - i_count; else s->b_error = true; } } else s->i_left -= i_count; } static inline uint32_t bs_read( bs_t *s, uint8_t i_count ) { uint8_t i_shr, i_drop = 0; uint32_t i_result = 0; if( i_count > 32 ) { i_drop = i_count - 32; i_count = 32; } while( i_count > 0 ) { if( bs_refill( s ) ) { s->b_error = true; break; } if( s->i_left > i_count ) { uint_fast32_t mask = (UINT64_C(1) << i_count) - 1; i_shr = s->i_left - i_count; /* more in the buffer than requested */ i_result |= ( *s->p >> i_shr ) & mask; s->i_left -= i_count; break; } else { uint_fast32_t mask = (UINT64_C(1) << s->i_left) - 1; i_shr = i_count - s->i_left; /* less in the buffer than requested */ if( i_shr >= 32 ) i_result = 0; else i_result |= (*s->p & mask) << i_shr; i_count -= s->i_left; s->i_left = 0; } } if( i_drop ) bs_skip( s, i_drop ); return( i_result ); } static inline uint32_t bs_read1( bs_t *s ) { if( bs_refill( s ) ) { s->b_error = true; return 0; } s->i_left--; return ( *s->p >> s->i_left )&0x01; } static inline void bs_write( bs_t *s, uint8_t i_count, uint32_t i_bits ) { if( s->b_read_only ) return; while( i_count > 0 ) { if( bs_refill( s ) ) { s->b_error = true; break; } i_count--; if( ( i_bits >> i_count )&0x01 ) { *s->p |= 1 << ( s->i_left - 1 ); } else { *s->p &= ~( 1 << ( s->i_left - 1 ) ); } s->i_left--; } } static inline bool bs_aligned( bs_t *s ) { return s->i_left % 8 == 0; } static inline void bs_align( bs_t *s ) { if( s->i_left % 8 ) s->i_left = 0; } static inline void bs_write_align( bs_t *s, uint8_t v ) { if( !s->b_read_only && (s->i_left % 8) ) bs_write( s, s->i_left, v ? 0xFF : 0 ); } #define bs_align_0( s ) bs_write_align( s, 0 ) #define bs_align_1( s ) bs_write_align( s, 1 ) /* Read unsigned Exp-Golomb code */ static inline uint_fast32_t bs_read_ue( bs_t * bs ) { unsigned i = 0; while( !bs->b_error && bs_read1( bs ) == 0 && bs->p < bs->p_end && i < 31 ) i++; return (1U << i) - 1 + bs_read( bs, i ); } /* Read signed Exp-Golomb code */ static inline int_fast32_t bs_read_se( bs_t *s ) { uint_fast32_t val = bs_read_ue( s ); return (val & 0x01) ? (int_fast32_t)((val + 1) / 2) : -(int_fast32_t)(val / 2); } #undef bs_forward #endif