I2C communication

unsigned char i2c_rx(char ack)
   {
   char x, d=0;
   SDA = 1;
   for(x=0; x<8; x++) {
      d <<= 1;
      do {  
         SCL = 1;
      }
      while(SCL_IN==0); // wait for any SCL clock stretching
      i2c_dly();
      if(SDA_IN) d |= 1;
      SCL = 0;
   }
   if(ack) SDA = 0;
   else SDA = 1;
   SCL = 1;
   i2c_dly(); // send (N)ACK bit
   SCL = 0;
   SDA = 1;
   return d;
}

in this program where i cant find any digitalread.....