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.