Sq10bit:   ;input in r0,r1; output in r2,r3,r4; both LSB first
   mov  a,r0    ;(a+b)^2=a^2+2*a*b+b^2
   mov  b,a
   mul  ab
   mov  r2,a
   mov  r3,b
   mov  a,r1
   mov  b,a
   mul  ab
   mov  r4,a
   mov  a,r1
   add  a,r1
   mov  b,r0
   mul  ab
   add  a,r3
   mov  r3,a
   mov  a,b
   addc a,r4
   mov  r4,a
   ret