mov -8($np,$num,8),%rax # np[num-1]
lea (%rsp),$ap # borrow ap for tp
shr \$62,%rax # check for boundary condition
+ lea -1($num),$j # j=num-1
jz .Lcopy
mov ($ap),%rax # tp[0]
- lea -1($num),$j # j=num-1
xor $i,$i # i=0 and clear CF!
jmp .Lsub
.align 16