Chief Delphi - My error derivative is going crazy

I'm trying to get PID control for the gyro working, and so far P is working fine. The D, however, is going to unreasonable values because my angle_err_last variable doesn't work at all. Here's my teleop.c function, sans gyro bias calc and printfs. I'm using the new code with C18 3.10.

Code:

void Teleop(void)

{

        #define KP 20/100;

        #define KD 0/10



        static unsigned int i = 0;

        static unsigned int j = 0;

        int temp_gyro_rate;

        long temp_gyro_angle;

        int temp_gyro_bias;

        long angle_err;

        long angle_err_last;

        long angle_err_d;

        long heading = 1800;

        long turn;



        i++;

        j++; // this will rollover every ~1000 seconds



             ...



                temp_gyro_bias = Get_Gyro_Bias();

                temp_gyro_rate = Get_Gyro_Rate();

                temp_gyro_angle = Get_Gyro_Angle();



        if(j >= 120)

        {

                temp_gyro_angle = gyro_cycle(temp_gyro_angle);

                angle_err = (heading - abs(temp_gyro_angle));



                angle_err_d = (angle_err - angle_err_last);



                



                turn = angle_err * KP + angle_err_d * KD;



                motor_left = limit(127 + turn);

                motor_right = limit(127 + turn);



        }





             ...





        angle_err_last = angle_err;



        Update_OI_LEDs();        // located in ifi_code.c

}

The P correction doesn't know left from right at the moment, but I'm not worried about that at the moment.

I set all of the variables as long to avoid type mismatches. The angle_err_last variable jumps all over the place, never coinciding with what angle_err actually was. Anyone know why?

edit: I commented out everything touching angle_err_last except for the declaration, and it still went all over the place.