STD
Set Direction Flag
| Opcode | Instruction | Op/En | 64-bit Mode | Compat/Leg Mode | Description |
|---|---|---|---|---|---|
| FD | STD | ZO | Valid | Valid | Set DF flag. |
Instruction Operand Encoding
| Op/En | Operand 1 | Operand 2 | Operand 3 | Operand 4 |
|---|---|---|---|---|
| ZO | N/A | N/A | N/A | N/A |
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.
This UNOFFICIAL, mechanically-separated, non-verified reference is provided for convenience, but it may be incomplete or broken in various obvious or non-obvious ways. Refer to Intel® 64 and IA-32 Architectures Software Developer’s Manual for anything serious.