Intel® Architecture Instruction Set Extensions Programming Reference

OPCODE MAP
• By this breakdown, it has been shown that this opcode represents the instruction: SHLD DS:00000000H, EAX,
3.
A.2.4.3 Three-Byte Opcode Instructions
The three-byte opcode maps shown in Table A-4 and Table A-5 includes primary opcodes that are either 3 or 4
bytes in length. Primary opcodes that are 3 bytes in length begin with two escape bytes 0F38H or 0F3A. The upper
and lower four bits of the third opcode byte are used to index a particular row and column in Table A-4 or Table A-5.
Three-byte opcodes that are 4 bytes in length begin with a mandatory prefix (66H, F2H, or F3H) and two escape
bytes (0F38H or 0F3AH). The upper and lower four bits of the fourth byte are used to index a particular row and
column in Table A-4 or Table A-5.
For each entry in the opcode map, the rules for interpreting the byte following the primary opcode fall into the
following case:
• A ModR/M byte is required and is interpreted according to the abbreviations listed in A.1 and Chapter 2,
“Instruction Format,” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A. The
operand types are listed according to notations listed in Section A.2.
Example A-3. Look-up Example for 3-Byte Opcodes
Look-up opcode 660F3A0FC108H for a PALIGNR instruction using Table A-5.
• 66H is a prefix and 0F3AH indicate to use Table A-5. The opcode is located in row 0, column F indicating a
PALIGNR instruction with operands Vdq, Wdq, and Ib. Interpret the operands as follows:
— Vdq: The reg field of the ModR/M byte selects a 128-bit XMM register.
— Wdq: The R/M field of the ModR/M byte selects either a 128-bit XMM register or memory location.
— Ib: Immediate data is encoded in the subsequent byte of the instruction.
• The next byte is the ModR/M byte (C1H). The reg field indicates that the first operand is XMM0. The mod shows
that the R/M field specifies a register and the R/M indicates that the second operand is XMM1.
• The last byte is the immediate byte (08H).
• By this breakdown, it has been shown that this opcode represents the instruction: PALIGNR XMM0, XMM1, 8.
A.2.4.4 VEX Prefix Instructions
Instructions that include a VEX prefix are organized relative to the 2-byte and 3-byte opcode maps, based on the
VEX.mmmmm field encoding of implied 0F, 0F38H, 0F3AH, respectively. Each entry in the opcode map of a VEXencoded
instruction is based on the value of the opcode byte, similar to non-VEX-encoded instructions.
A VEX prefix includes several bit fields that encode implied 66H, F2H, F3H prefix functionality (VEX.pp) and
operand size/opcode information (VEX.L). See chapter 4 for details.
Opcode tables A2-A6 include both instructions with a VEX prefix and instructions without a VEX prefix. Many entries
are only made once, but represent both the VEX and non-VEX forms of the instruction. If the VEX prefix is present
all the operands are valid and the mnemonic is usually prefixed with a “v”. If the VEX prefix is not present the
VEX.vvvv operand is not available and the prefix “v” is dropped from the mnemonic.
A few instructions exist only in VEX form and these are marked with a superscript “v”.
Operand size of VEX prefix instructions can be determined by the operand type code. 128-bit vectors are indicated
by 'dq', 256-bit vectors are indicated by 'qq', and instructions with operands supporting either 128 or 256-bit,
determined by VEX.L, are indicated by 'x'. For example, the entry "VMOVUPD Vx,Wx" indicates both VEX.L=0 and
VEX.L=1 are supported.
Ref. # 319433-014 A-5