A.5.58 DEC: Decrement Integer
DEC reg16 ; o16 48+r [8086]
DEC reg32 ; o32 48+r [386]
DEC r/m8 ; FE /1 [8086]
DEC r/m16 ; o16 FF /1 [8086]
DEC r/m32 ; o32 FF /1 [386]
DEC subtracts 1 from its operand. It does _not_ affect the carry flag:
to affect the carry flag, use SUB something,1 (see section A.5.305). DEC
affects all the other flags according to the result.
This instruction can be used with a LOCK prefix to allow atomic
execution.
See also INC (section A.5.120).