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#include <math.h>


UINT Ue(BYTE *pBuff, UINT nLen, UINT &nStartBit)
{
	//计算0bit的个数
	UINT nZeroNum = 0;
	while (nStartBit < nLen * 8)
	{
		if (pBuff[nStartBit / 8] & (0x80 >> (nStartBit % 8))) //&:按位与，%取余
		{
			break;
		}
		nZeroNum++;
		nStartBit++;
	}
	nStartBit ++;

	//计算结果
	DWORD dwRet = 0;
	for (UINT i=0; i<nZeroNum; i++)
	{
		dwRet <<= 1;
		if (pBuff[nStartBit / 8] & (0x80 >> (nStartBit % 8)))
		{
			dwRet += 1;
		}
		nStartBit++;
	}
	return (1 << nZeroNum) - 1 + dwRet;
}


int Se(BYTE *pBuff, UINT nLen, UINT &nStartBit)
{
	int UeVal=Ue(pBuff,nLen,nStartBit);
	double k=UeVal;
	int nValue=ceil(k/2);//ceil函数：ceil函数的作用是求不小于给定实数的最小整数。ceil(2)=ceil(1.2)=cei(1.5)=2.00
	if (UeVal % 2==0)
		nValue=-nValue;
	return nValue;


}

DWORD u(UINT BitCount,BYTE * buf,UINT &nStartBit)
{
	DWORD dwRet = 0;
	for (UINT i=0; i<BitCount; i++)
	{
		dwRet <<= 1;
		if (buf[nStartBit / 8] & (0x80 >> (nStartBit % 8)))
		{
			dwRet += 1;
		}
		nStartBit++;
	}
	return dwRet;
}


/************************************************************************/
/* 解析SPS获取分辨率
  buf：除去00 00 00 01之后的部分，从67开始                              */
/************************************************************************/
bool h264_decode_seq_parameter_set(BYTE * buf,UINT nLen,int &Width,int &Height)
{
	UINT StartBit=0; 
	int forbidden_zero_bit=u(1,buf,StartBit);
	int nal_ref_idc=u(2,buf,StartBit);
	int nal_unit_type=u(5,buf,StartBit);
	if(nal_unit_type==7)
	{
		int profile_idc=u(8,buf,StartBit);
		int constraint_set0_flag=u(1,buf,StartBit);//(buf[1] & 0x80)>>7;
		int constraint_set1_flag=u(1,buf,StartBit);//(buf[1] & 0x40)>>6;
		int constraint_set2_flag=u(1,buf,StartBit);//(buf[1] & 0x20)>>5;
		int constraint_set3_flag=u(1,buf,StartBit);//(buf[1] & 0x10)>>4;
		int reserved_zero_4bits=u(4,buf,StartBit);
		int level_idc=u(8,buf,StartBit);

		int seq_parameter_set_id=Ue(buf,nLen,StartBit);

		if( profile_idc == 100 || profile_idc == 110 ||
			profile_idc == 122 || profile_idc == 144 )
		{
			int chroma_format_idc=Ue(buf,nLen,StartBit);
			if( chroma_format_idc == 3 )
				int residual_colour_transform_flag=u(1,buf,StartBit);
			int bit_depth_luma_minus8=Ue(buf,nLen,StartBit);
			int bit_depth_chroma_minus8=Ue(buf,nLen,StartBit);
			int qpprime_y_zero_transform_bypass_flag=u(1,buf,StartBit);
			int seq_scaling_matrix_present_flag=u(1,buf,StartBit);

			int seq_scaling_list_present_flag[8];
			if( seq_scaling_matrix_present_flag )
			{
				for( int i = 0; i < 8; i++ ) {
					seq_scaling_list_present_flag[i]=u(1,buf,StartBit);
				}
			}
		}
		int log2_max_frame_num_minus4=Ue(buf,nLen,StartBit);
		int pic_order_cnt_type=Ue(buf,nLen,StartBit);
		if( pic_order_cnt_type == 0 )
			int log2_max_pic_order_cnt_lsb_minus4=Ue(buf,nLen,StartBit);
		else if( pic_order_cnt_type == 1 )
		{
			int delta_pic_order_always_zero_flag=u(1,buf,StartBit);
			int offset_for_non_ref_pic=Se(buf,nLen,StartBit);
			int offset_for_top_to_bottom_field=Se(buf,nLen,StartBit);
			int num_ref_frames_in_pic_order_cnt_cycle=Ue(buf,nLen,StartBit);

			int *offset_for_ref_frame=new int[num_ref_frames_in_pic_order_cnt_cycle];
			for( int i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; i++ )
				offset_for_ref_frame[i]=Se(buf,nLen,StartBit);
			delete [] offset_for_ref_frame;
		}
		int num_ref_frames=Ue(buf,nLen,StartBit);
		int gaps_in_frame_num_value_allowed_flag=u(1,buf,StartBit);
		int pic_width_in_mbs_minus1=Ue(buf,nLen,StartBit);
		int pic_height_in_map_units_minus1=Ue(buf,nLen,StartBit);

		Width=(pic_width_in_mbs_minus1+1)*16;
		Height=(pic_height_in_map_units_minus1+1)*16;

		return true;
	}
	else
		return false;
}