dest = -dest
The neg instruction performs the 2's complement negation of its operand. The operand can be a register or a memory address.
neg r9 ; negate r9 neg eax ; negate eax ; upper half of rax will be 0 neg r8b ; negate r8b ; leave the rest of r8 as is neg dword [x] ; negate the 32 bit variable x
CF is set to 0 if the result is 0 and 1 otherwise.