x86doc › AESKEYGENASSIST - AES Round Key Generation Assist

AESKEYGENASSIST—AES Round Key Generation Assist

Opcode/Instruction	Op/En	64/32-bit Mode	CPUID Feature Flag	Description
66 0F 3A DF /r ib AESKEYGENASSIST xmm1, xmm2/m128, imm8	RMI	V/V	AES	Assist in AES round key generation using an 8 bits Round Constant (RCON) specified in the immediate byte, operating on 128 bits of data specified in xmm2/m128 and stores the result in xmm1.
VEX.128.66.0F3A.WIG DF /r ib VAESKEYGENASSIST xmm1, xmm2/m128, imm8	RMI	V/V	Both AES and AVX flags	Assist in AES round key generation using 8 bits Round Constant (RCON) specified in the immediate byte, operating on 128 bits of data specified in xmm2/m128 and stores the result in xmm1.

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
RMI	ModRM:reg (w)	ModRM:r/m (r)	imm8	N/A

Description

Assist in expanding the AES cipher key, by computing steps towards generating a round key for encryption, using 128-bit data specified in the source operand and an 8-bit round constant specified as an immediate, store the result in the destination operand.

The destination operand is an XMM register. The source operand can be an XMM register or a 128-bit memory loca-tion.

128-bit Legacy SSE version: Bits (MAXVL-1:128) of the corresponding YMM destination register remain unchanged.

VEX.128 encoded version: Bits (MAXVL-1:128) of the destination YMM register are zeroed.

Note: In VEX-encoded versions, VEX.vvvv is reserved and must be 1111b, otherwise instructions will #UD.

Operation

AESKEYGENASSIST

X3[31:0] := SRC [127: 96];
X2[31:0] := SRC [95: 64];
X1[31:0] := SRC [63: 32];
X0[31:0] := SRC [31: 0];
RCON[31:0] := ZeroExtend(imm8[7:0]);
DEST[31:0] := SubWord(X1);
DEST[63:32 ] := RotWord( SubWord(X1) ) XOR RCON;
DEST[95:64] := SubWord(X3);
DEST[127:96] := RotWord( SubWord(X3) ) XOR RCON;
DEST[MAXVL-1:128] (Unmodified)

VAESKEYGENASSIST

X3[31:0] := SRC [127: 96];
X2[31:0] := SRC [95: 64];
X1[31:0] := SRC [63: 32];
X0[31:0] := SRC [31: 0];
RCON[31:0] := ZeroExtend(imm8[7:0]);
DEST[31:0] := SubWord(X1);
DEST[63:32 ] := RotWord( SubWord(X1) ) XOR RCON;
DEST[95:64] := SubWord(X3);
DEST[127:96] := RotWord( SubWord(X3) ) XOR RCON;
DEST[MAXVL-1:128] := 0;

Intel C/C++ Compiler Intrinsic Equivalent

(V)AESKEYGENASSIST __m128i _mm_aeskeygenassist (__m128i, const int)

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Table 2-21, “Type 4 Class Exception Conditions,” additionally:

#UD	If VEX.vvvv ≠ 1111B.