DEC subtracts 1 from its operand. It does not affect the
carry flag: to affect the carry flag, use SUB something,1 (see
SUB). 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 (INC).
Every form of dec the assembler accepts.
| Form | Since | Notes |
|---|---|---|
| dec reg16 | 8086 | nolong |
| dec reg32 | 386 | nolong |
| dec r/m8 | 8086 | lock |
| dec r/m16 | 8086 | lock |
| dec r/m32 | 386 | lock |
| dec r/m64 | x86-64 | locklong |
| dec [reg8], r/m8 | x86-64 | apxlocklong |
| dec [reg16], r/m16 | x86-64 | apxlocklong |
| dec [reg32], r/m32 | x86-64 | apxlocklong |
| dec [reg64], r/m64 | x86-64 | apxlocklong |
