DEC

Table of Contents

1. DEC (dec)
   1. Basic function
   2. Instruction execution process
   3. Instruction format
   4. Behavioral characteristics
   5. Common uses

DEC (dec)

Basic function

Performs -1 on the operand:
dest = dest - 1

Instruction execution process

• Subtract 1 from the destination operand
• Update all flags except CF (different from SUB x,1)

Instruction format

1
dec r/m8
2
dec r/m16
3
dec r/m32
4
dec r/m64

Behavioral characteristics

• Does not modify CF
• Modifies other common flags (ZF, SF, OF, PF, AF)
• Symmetrical with INC
• Used for loop decrements, countdown counters, etc.

Common uses

• Common reverse pattern in for-loops
• Move a pointer backward
• Countdown control in state machines
• Simple counter decrement