std

Set Direction Flag

STD

Sets DF to 1 (String operations decrement).

Pseudocode Operation

DF ← 1

Encoding

Binary Layout

FD

+0

 

Format Legacy

Opcode FD

Extension Base

Operands

Related

More in Base

Reference

View in Intel® 64 and IA-32 Architectures SDM ↗ Intel® SDM

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
FD	STD	ZO	Valid Valid		Set DF flag.

Description

Sets the DF flag in the EFLAGS register. When the DF flag is set to 1, string operations decrement the index registers (ESI and/or EDI). Operation is the same in all modes.

Operation

DF := 1;

Flags Affected

The DF flag is set. The CF, OF, ZF, SF, AF, and PF flags are unaffected. Exceptions (All Operating Modes) #UD If the LOCK prefix is used. STD-Set Direction Flag Vol. 2B 4-672