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Vol. 2A 3-7
INSTRUCTION SET REFERENCE, A-M
• N.P. — Indicates the REX prefix does not affect the legacy instruction in 64-bit
mode.
• N.I. — Indicates the opcode is treated as a new instruction in 64-bit mode.
• N.S. — Indicates an instruction syntax that requires an address override prefix in
64-bit mode and is not supported. Using an address override prefix in 64-bit
mode may result in model-specific execution behavior.
3.1.1.4 Compatibility/Legacy Mode Column in the Instruction Summary
Table
The “Compatibility/Legacy Mode” column provides information on the opcode
sequence in either the compatibility mode or other IA-32 modes. The column uses
the following notation:
• Valid — Supported.
• Invalid — Not supported.
• N.E. — Indicates an Intel 64 instruction mnemonics/syntax that is not
encodable; the opcode sequence is not applicable as an individual instruction in
compatibility mode or IA-32 mode. The opcode may represent a valid sequence
of legacy IA-32 instructions.
3.1.1.5 Description Column in the Instruction Summary Table
The “Description” column briefly explains forms of the instruction.
3.1.1.6 Description Section
Each instruction is then described by number of information sections. The “Descrip-
tion” section describes the purpose of the instructions and required operands in more
detail.
3.1.1.7 Operation Section
The “Operation” section contains an algorithm description (frequently written in
pseudo-code) for the instruction. Algorithms are composed of the following
elements:
• Comments are enclosed within the symbol pairs “(*” and “*)”.
• Compound statements are enclosed in keywords, such as: IF, THEN, ELSE and FI
for an if statement; DO and OD for a do statement; or CASE... OF for a case
statement.
• A register name implies the contents of the register. A register name enclosed in
brackets implies the contents of the location whose address is contained in that
register. For example, ES:[DI] indicates the contents of the location whose ES
segment relative address is in register DI. [SI] indicates the contents of the