vpermi2b

Permute Two-Source Bytes

VPERMI2B zmm1 {k1}, zmm2, zmm3/m512

Shuffles bytes from two ZMM registers into destination.

Details

Permutes bytes from two ZMM registers (destination and source) using byte indices in the second source, storing results in the destination. The instruction performs a gather-like operation where each byte index selects from either the destination or source register based on the high bit. No flags are modified; the operation is masked by the opmask register k1, with zeroing or merging semantics.

Pseudocode Operation

for i = 0 to 63:
  idx = zmm2[8*i:8*i+7]
  if idx[7] == 0:
    zmm1[8*i:8*i+7] ← zmm1[8*(idx[6:0]):8*(idx[6:0])+7]
  else:
    zmm1[8*i:8*i+7] ← zmm3[8*(idx[6:0]):8*(idx[6:0])+7]
  zmm1[8*i:8*i+7] ← zmm1[8*i:8*i+7] & k1_mask[i]

Example

VPERMI2B zmm1, zmm2, zmm3/m512

Encoding

Binary Layout

EVEX

Format EVEX

Opcode EVEX.512.66.0F38.W0 75 /r

Extension AVX-512-VBMI

Operands

dest
ZMM
idx
ZMM
src
ZMM/Mem

Reference (Intel® SDM)

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
EVEX.128.66.0F38.W0 75 /r	VPERMI2B xmm1 {k1}{z}, xmm2, xmm3/m128	A	V/V	(AVX512VL AND AVX512_VBMI) OR AVX10.1	Permute bytes in xmm3/m128 and xmm2 using byte indexes in xmm1 and store the byte results in xmm1 using writemask k1.
EVEX.256.66.0F38.W0 75 /r	VPERMI2B ymm1 {k1}{z}, ymm2, ymm3/m256	A	V/V	(AVX512VL AVX512_VBMI) OR AVX10.1	Permute bytes in ymm3/m256 and ymm2 using byte indexes in ymm1 and store the byte results in ymm1 using writemask k1.
EVEX.512.66.0F38.W0 75 /r	VPERMI2B zmm1 {k1}{z}, zmm2, zmm3/m512	A	V/V	AVX512_VBMI OR AVX10.1	Permute bytes in zmm3/m512 and zmm2 using byte indexes in zmm1 and store the byte results in zmm1 using writemask k1.

Instruction Operand Encoding

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

Description

Permutes byte values in the second operand (the first source operand) and the third operand (the second source operand) using the byte indices in the first operand (the destination operand) to select byte elements from the second or third source operands. The selected byte elements are written to the destination at byte granularity under the writemask k1. The first and second operands are ZMM/YMM/XMM registers. The first operand contains input indices to select elements from the two input tables in the 2nd and 3rd operands. The first operand is also the destination of the result. The third operand can be a ZMM/YMM/XMM register, or a 512/256/128-bit memory location. In each index byte, the id bit for table selection is bit 6/5/4, and bits [5:0]/[4:0]/[3:0] selects element within each input table. Note that these instructions permit a byte value in the source operands to be copied to more than one location in the destination operand. Also, the same tables can be reused in subsequent iterations, but the index elements are overwritten. Bits (MAX_VL-1:256/128) of the destination are zeroed for VL=256,128. VPERMI2B—Full Permute of Bytes From Two Tables Overwriting the Index Vol. 2C 5-503

Operation

VPERMI2B (EVEX encoded versions)
(KL, VL) = (16, 128), (32, 256), (64, 512)
IF VL = 128:
id := 3;
ELSE IF VL = 256:
id := 4;
ELSE IF VL = 512:
id := 5;
FI;
TMP_DEST[VL-1:0] := DEST[VL-1:0];
FOR j := 0 TO KL-1
off := 8*SRC1[j*8 + id: j*8] ;
IF k1[j] OR *no writemask*:
DEST[j*8 + 7: j*8] := TMP_DEST[j*8+id+1]? SRC2[off+7:off] : SRC1[off+7:off];
ELSE IF *zeroing-masking*
DEST[j*8 + 7: j*8] := 0;
*ELSE
DEST[j*8 + 7: j*8] remains unchanged*
FI;
ENDFOR
DEST[MAX_VL-1:VL] := 0;

Intel C/C++ Compiler Intrinsic Equivalent

VPERMI2B __m512i _mm512_permutex2var_epi8(__m512i a, __m512i idx, __m512i b);
VPERMI2B __m512i _mm512_mask2_permutex2var_epi8(__m512i a, __m512i idx, __mmask64 k, __m512i b);
VPERMI2B __m512i _mm512_maskz_permutex2var_epi8(__mmask64 k, __m512i a, __m512i idx, __m512i b);
VPERMI2B __m256i _mm256_permutex2var_epi8(__m256i a, __m256i idx, __m256i b);
VPERMI2B __m256i _mm256_mask2_permutex2var_epi8(__m256i a, __m256i idx, __mmask32 k, __m256i b);
VPERMI2B __m256i _mm256_maskz_permutex2var_epi8(__mmask32 k, __m256i a, __m256i idx, __m256i b);
VPERMI2B __m128i _mm_permutex2var_epi8(__m128i a, __m128i idx, __m128i b);
VPERMI2B __m128i _mm_mask2_permutex2var_epi8(__m128i a, __m128i idx, __mmask16 k, __m128i b);
VPERMI2B __m128i _mm_maskz_permutex2var_epi8(__mmask16 k, __m128i a, __m128i idx, __m128i b);

Exceptions

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Exceptions Type E4NF.nb in Table 2-52, “Type E4NF Class Exception Conditions.” VPERMI2B—Full Permute of Bytes From Two Tables Overwriting the Index Vol. 2C 5-504