Intel 64 and IA-32 Architectures Software Developers Manual Volume 2B, Instruction Set Reference, N-Z

Vol. 2B 4-331
INSTRUCTION SET REFERENCE, N-Z
STD—Set Direction 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).
This instruction’s operation is the same in non-64-bit modes and 64-bit mode.
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)
None.
Opcode Instruction
64-Bit
Mode
Compat/
Leg Mode Description
FD STD Valid Valid Set DF flag.