#include <reg51.h>
	unsigned int a;
	unsigned long s; // long for overflow prevention.

main()
{
	char i;
	a = P0;	 // 0x0000 aaaa
	a <<= 8; // 0xaaaa 0000
	s = P1;  // 0x0000 0000 bbbb
	
	for( i = 0; i < 8; i++ ) {
			if( s & 0x0001 ) 
				s += a;
			s >>= 1;
	}
	P2 = s;
	P3 = s >> 8;
	while(1);
}