cld

Clear Direction Flag

CLD

Sets DF to 0 (String operations increment).

Details

Clears the Direction Flag (DF) to 0, causing string instructions (MOVS, SCAS, LODS, STOS, CMPS) to auto-increment the index registers (ESI/EDI or RSI/RDI) rather than decrement them. Only DF is modified; all other flags remain unchanged. Available in all modes.

Pseudocode Operation

DF ← 0

Example

CLD

Encoding

Binary Layout
FC
+0
 
Format Legacy
Opcode FC
Extension Base

Operands

Reference (Intel® SDM)

Instruction Forms

Opcode Instruction Op/En 64/32-bit Mode CPUID Description
FC CLD ZO Valid Valid Clear DF flag.

Description

Clears the DF flag in the EFLAGS register. When the DF flag is set to 0, string operations increment the index registers (ESI and/or EDI). Operation is the same in all modes.

Operation

DF := 0;

Flags Affected

The DF flag is set to 0. The CF, OF, ZF, SF, AF, and PF flags are unaffected. Exceptions (All Operating Modes) #UD If the LOCK prefix is used. CLD—Clear Direction Flag Vol. 2A 3-141