/*********************************************************
*    Pseudo-random number generator - PN Sequence        *
*********************************************************/
static int shift_reg;   

int pn_sequence(int *sreg)
{
    int b2,b12,b15;
    int t1,t2;   
             
    b15 = *sreg >>15;
    b12 = *sreg >>11;
    t2 = b15^b12;          // The first XOR bit15 and bit12
    b2 = *sreg >>2;
    t1 = *sreg ^b2;        // The second XOR bit2 and bit0
    t2 = t1^t2;            // The final XOR 
    t2 &= 1;
    *sreg = *sreg <<1;
    *sreg = *sreg |t2;     // Update the register
    t2 = *sreg-0x4000;     // Zero mean random number
    return t2;
}