avoider robot

i need help.
i get this source code

#include <at89x51.h>
#include <delay.h>
#define usi P3_2 // ultrasonic in
#define uso P3_3 // ultrasonic out

unsigned char i;
bit x;

at 0x90 sbit md1; // left
at 0x91 sbit me1; //
at 0x92 sbit md2; // right
at 0x93 sbit me2; //

void cek_jarak()
{ TH0 = 0x00;
TL0 = 0x00;
TF0 = 0;
TF1 = 0;
usi = 1;
TR1 = 1;
while(!TF1);
TR1 = 0;
usi = 0;
while(!uso);
TR0 = 1;
while(uso);
TR0 = 0;
}

void perjalanan(bit a, bit b, bit c, bit d)
{me1= a; me2= b; md1= c; md2= d;}

void main()
{ TMOD = 0x21 ;
TCON = 0x00 ;
TH1 = 100;
while(1)
{ cek_jarak();
if(TH0 > 0x00) perjalanan(0,0,1,1);// forward
else
{ perjalanan(0,0,0,0);// backward
for(i=0; i<100; i++)delay(6000);
perjalanan(0,0,x,~x);// turn right/left
for(i=0; i<100; i++)delay(6000);
} x = ~x;
} }

but i cannot compile it.
can anybody help?