Code for built-in 10-bit AD conversion in STC microcontroller + [software filtering]

GetResult() is software filtering. I always got errors when filtering 10-bit AD before. I just got it right today.
The key is (unsigned long)(). If you don't add this, you will always get errors! Overflow during calculation, it seems that the bit is automatically reduced during calculation
 

ulong GetADCResult(uchar ch)
{
ulong AD_result;
ADC_CONTR = ADC_POWER | ADC_SPEEDLL | ch | ADC_START;
    _nop_(); //Must wait before inquiry
    _nop_();
    _nop_();
    _nop_();
    while (!(ADC_CONTR & ADC_FLAG));//Wait complete flag
    ADC_CONTR &= ~ADC_FLAG; //Close ADC
AD_result=ADC_RES*4+ADC_RESL;

    return AD_result; //Return ADC result 10bit
}
ulong GetResult(uchar ch) //Filter segment
{
ulong AD_result=0,AD_result1=0;
ulong AD_max,AD_min,AD_temp;
char AD_i,AD_o;

for(AD_i=0;AD_i<4;AD_i++)
{
AD_min=AD_max=GetADCResult(ch);
AD_result=0;
for(AD_o=0;AD_o<8;AD_o++)
{
AD_temp=GetADCResult(ch);
if(AD_tempAD_max){AD_result =(unsigned long)(AD_result + (unsigned long)AD_max); AD_max=AD_temp;}
      else
    AD_result =(unsigned long)(AD_result + (unsigned long)AD_temp);
  }
AD_result=(unsigned long)(AD_result/8);

AD_result1=AD_result1+ (unsigned long)(AD_result);
}
AD_result1=(unsigned long)(AD_result1/4);

return AD_result; //Return ADC result 10bit
}

The method is based on: removing the maximum and minimum values ​​and averaging. A total of 33 samples were taken and the average value of the results after removing 9 samples was obtained. I made the voltmeter myself and the speed is sufficient! If it is too slow, you can reduce the 4 in AD_i<4 or remove this loop.