myvtm/Other/libvideoframework/bs.h

#ifndef _BS_H_
#define _BS_H_

#include <stdio.h>
#include <stdint.h>

typedef struct bs_s
{
	uint8_t *p_start;					// 缓冲区首地址
	uint8_t *p;                         // 缓冲区当前的读写指针
	uint8_t *p_end;						// 缓冲区尾地址
	uint8_t  i_left;					// p所指字节当前还有多少比特可读写
	uint8_t  i_bits_encoded;			// RD only 
} bs_t;

//使用p_data指向的i_data个字节作为缓冲区初始化比特流s
void bs_init( bs_t *s, void *p_data, int i_data)
{
	s->p_start = (uint8_t*)p_data;
	s->p       = (uint8_t*)p_data;
	s->p_end   = s->p + i_data;
	s->i_left  = 8;
}
	
//从比特流s中读出i_count个比特的值并返回
static uint32_t bs_read( bs_t *s, int i_count)
{
	static uint32_t i_mask[33] ={
		0x00,
		0x01,      0x03,      0x07,      0x0f,
		0x1f,      0x3f,      0x7f,      0xff,
		0x1ff,     0x3ff,     0x7ff,     0xfff,
		0x1fff,    0x3fff,    0x7fff,    0xffff,
		0x1ffff,   0x3ffff,   0x7ffff,   0xfffff,
		0x1fffff,  0x3fffff,  0x7fffff,  0xffffff,
		0x1ffffff, 0x3ffffff, 0x7ffffff, 0xfffffff,
		0x1fffffff,0x3fffffff,0x7fffffff,0xffffffff
	};

	int      i_shr = 0;
	uint32_t u_shr = 0;
	uint32_t i_result = 0;

	while( i_count > 0 ){
		if( s->p >= s->p_end ){
			break;
		}

		if( ( i_shr = s->i_left - i_count ) >= 0 ){
			/* more in the buffer than requested */
			u_shr = i_shr;
			i_result |= ( *s->p >> u_shr )&i_mask[i_count];
			s->i_left -= i_count;
			if( s->i_left == 0 )
			{
				s->p++;
				s->i_left = 8;
			}
			return( i_result );
		}
		else
		{
			/* less in the buffer than requested */
			u_shr = -i_shr;
			i_result |= (*s->p&i_mask[s->i_left]) << u_shr;
			i_count  -= s->i_left;
			s->p++;
			s->i_left = 8;
		}
	}
	return(i_result);
}

//从比特流s中读出1个比特并返回
static uint32_t bs_read1( bs_t *s)
{
	if( s->p < s->p_end )
	{
		uint32_t i_result;
		s->i_left--;
		i_result = ( *s->p >> s->i_left )&0x01;
		if( s->i_left == 0 )
		{
			s->p++;
			s->i_left = 8;
		}
		return i_result;
	}
	return 0;
}

static int bs_read_ue( bs_t *s)
{
	uint8_t i = 0;
	while( bs_read1( s ) == 0 && s->p < s->p_end && i < 32 )
	{
		i++;
	}
	return( ( 1 << i) - 1 + bs_read(s,i));
}

#endif