STD

STD

Intel Architecture Software Developer's Manual (July 2017)

STD - Set Direction Flag

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

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
ZO	NA	NA	NA	NA

Description

Sets the DF flag in the EFLAGS register. When the DF flag is set to 1, string operations decrement the index regis- ters (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.