Arm Cortex Programming

I am new to embedded coding. I am working on aduc microcontroller.

Can anyone explain to me what this code is doing?

int DioCfgPin(ADI_GPIO_TypeDef *pPort, int iPin, int iMode)
{  
   unsigned short a = pPort->GPCON;
   a &= (0xFFFF - (0x3 << (2 * iPin)));   // keep all configurations except iPin
   a += (iMode << (2 * iPin));            // configure iPin
   pPort->GPCON = a;
   return 1;
}