gf2p8affineqb

Galois Field Affine Transformation

GF2P8AFFINEQB xmm1, xmm2/m128, imm8

Computes affine transformation in GF(2^8).

Details

Performs byte-wise affine transformation in Galois Field GF(2^8) on 128-bit XMM operands using a constant 8-bit immediate as the affine constant. Each byte in the destination is transformed using the corresponding byte from the source operand. No flags are affected; this is a pure data-parallel cryptographic operation.

Pseudocode Operation

for i in 0..15:
  dest[i] ← GF2P8_AFFINE_TRANSFORM(dest[i], src[i], imm8);

Example

GF2P8AFFINEQB xmm1, xmm2/m128, 3

Encoding

Binary Layout

Format VEX

Opcode 66 0F 3A CE /r ib

Extension GFNI

Operands

dest
128-bit XMM SIMD register
src1
128-bit XMM SIMD register or Memory operand
src2
8-bit signed immediate

Reference (Intel® SDM)

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
VEX.128.66.0F3A.W1 CE /r /ib	VGF2P8AFFINEQB xmm1, xmm2, xmm3/m128, imm8	B	V/V	AVX GFNI	Computes affine transformation in the finite field GF(2^8).
VEX.256.66.0F3A.W1 CE /r /ib	VGF2P8AFFINEQB ymm1, ymm2, ymm3/m256, imm8	B	V/V	AVX GFNI	Computes affine transformation in the finite field GF(2^8).
EVEX.128.66.0F3A.W1 CE /r /ib	VGF2P8AFFINEQB xmm1{k1}{z}, xmm2, xmm3/m128/m64bcst, imm8	C	V/V	(AVX512VL OR AVX10.1) GFNI	Computes affine transformation in the finite field GF(2^8).
EVEX.256.66.0F3A.W1 CE /r /ib	VGF2P8AFFINEQB ymm1{k1}{z}, ymm2, ymm3/m256/m64bcst, imm8	C	V/V	(AVX512VL OR AVX10.1) GFNI	Computes affine transformation in the finite field GF(2^8).
EVEX.512.66.0F3A.W1 CE /r /ib	VGF2P8AFFINEQB zmm1{k1}{z}, zmm2, zmm3/m512/m64bcst, imm8	C	V/V	(AVX512F OR AVX10.1) GFNI	Computes affine transformation in the finite field GF(2^8).

Instruction Operand Encoding

Op/En	Tuple Type	Operand 1	Operand 2	Operand 3	Operand 4
A	N/A	ModRM:reg (r, w)	ModRM:r/m (r)	imm8 (r)	N/A
B	N/A	ModRM:reg (w)	VEX.vvvv (r)	ModRM:r/m (r)	imm8 (r)
C	Full	ModRM:reg (w)	EVEX.vvvv (r)	ModRM:r/m (r)	imm8 (r)

Description

The AFFINEB instruction computes an affine transformation in the Galois Field 28. For this instruction, an affine transformation is defined by A * x + b where “A” is an 8 by 8 bit matrix, and “x” and “b” are 8-bit vectors. One SIMD register (operand 1) holds “x” as either 16, 32 or 64 8-bit vectors. A second SIMD (operand 2) register or memory operand contains 2, 4, or 8 “A” values, which are operated upon by the correspondingly aligned 8 “x” values in the first register. The “b” vector is constant for all calculations and contained in the immediate byte. The EVEX encoded form of this instruction does not support memory fault suppression. The SSE encoded forms of the instruction require16B alignment on their memory operations.

Operation

define parity(x):
t := 0                // single bit
FOR i := 0 to 7:
t = t xor x.bit[i]
return t

define affine_byte(tsrc2qw, src1byte, imm):
FOR i := 0 to 7:
* parity(x) = 1 if x has an odd number of 1s in it, and 0 otherwise.*
retbyte.bit[i] := parity(tsrc2qw.byte[7-i] AND src1byte) XOR imm8.bit[i]
return retbyte



GF2P8AFFINEQB—Galois Field Affine Transformation                                                                                           Vol. 2A 3-429
VGF2P8AFFINEQB dest, src1, src2, imm8 (EVEX Encoded Version)
(KL, VL) = (2, 128), (4, 256), (8, 512)
FOR j := 0 TO KL-1:
IF SRC2 is memory and EVEX.b==1:
tsrc2 := SRC2.qword[0]
ELSE:
tsrc2 := SRC2.qword[j]

FOR b := 0 to 7:
IF k1[j*8+b] OR *no writemask*:
DEST.qword[j].byte[b] := affine_byte(tsrc2, SRC1.qword[j].byte[b], imm8)
ELSE IF *zeroing*:
DEST.qword[j].byte[b] := 0
*ELSE DEST.qword[j].byte[b] remains unchanged*
DEST[MAX_VL-1:VL] := 0

VGF2P8AFFINEQB dest, src1, src2, imm8 (128b and 256b VEX Encoded Versions)
(KL, VL) = (2, 128), (4, 256)
FOR j := 0 TO KL-1:
FOR b := 0 to 7:
DEST.qword[j].byte[b] := affine_byte(SRC2.qword[j], SRC1.qword[j].byte[b], imm8)
DEST[MAX_VL-1:VL] := 0

GF2P8AFFINEQB srcdest, src1, imm8 (128b SSE Encoded Version)
FOR j := 0 TO 1:
FOR b := 0 to 7:
SRCDEST.qword[j].byte[b] := affine_byte(SRC1.qword[j], SRCDEST.qword[j].byte[b], imm8)

Intel C/C++ Compiler Intrinsic Equivalent

(V)GF2P8AFFINEQB __m128i _mm_gf2p8affine_epi64_epi8(__m128i, __m128i, int);
(V)GF2P8AFFINEQB __m128i _mm_mask_gf2p8affine_epi64_epi8(__m128i, __mmask16, __m128i, __m128i, int);
(V)GF2P8AFFINEQB __m128i _mm_maskz_gf2p8affine_epi64_epi8(__mmask16, __m128i, __m128i, int);
VGF2P8AFFINEQB __m256i _mm256_gf2p8affine_epi64_epi8(__m256i, __m256i, int);
VGF2P8AFFINEQB __m256i _mm256_mask_gf2p8affine_epi64_epi8(__m256i, __mmask32, __m256i, __m256i, int);
VGF2P8AFFINEQB __m256i _mm256_maskz_gf2p8affine_epi64_epi8(__mmask32, __m256i, __m256i, int);
VGF2P8AFFINEQB __m512i _mm512_gf2p8affine_epi64_epi8(__m512i, __m512i, int);
VGF2P8AFFINEQB __m512i _mm512_mask_gf2p8affine_epi64_epi8(__m512i, __mmask64, __m512i, __m512i, int);
VGF2P8AFFINEQB __m512i _mm512_maskz_gf2p8affine_epi64_epi8(__mmask64, __m512i, __m512i, int);

Exceptions

SIMD Floating-Point Exceptions

None.

Other Exceptions

Legacy-encoded and VEX-encoded: See Table 2-21, “Type 4 Class Exception Conditions.” EVEX-encoded: See Table 2-52, “Type E4NF Class Exception Conditions.” GF2P8AFFINEQB—Galois Field Affine Transformation Vol. 2A 3-430