vpermt2b

Permute Two-Source Bytes (Overwrite)

VPERMT2B zmm1 {k1}, zmm2, zmm3/m512

Shuffles bytes from two sources, overwriting index.

Details

Permutes bytes from two sources using indices in the destination register (which is overwritten), selecting from either the index register or the second source based on the index's high bit. This is the two-operand form where indices reside in what becomes the output. No flags are modified; masking via k1 applies to the result with optional zeroing.

Pseudocode Operation

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

Example

VPERMT2B zmm1, zmm2, zmm3/m512

Encoding

Binary Layout

EVEX

Format EVEX

Opcode EVEX.512.66.0F38.W0 7D /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 7D /r	VPERMT2B xmm1 {k1}{z}, xmm2, xmm3/m128	A	V/V	(AVX512VL AND AVX512_VBMI) OR AVX10.1	Permute bytes in xmm3/m128 and xmm1 using byte indexes in xmm2 and store the byte results in xmm1 using writemask k1.
EVEX.256.66.0F38.W0 7D /r	VPERMT2B ymm1 {k1}{z}, ymm2, ymm3/m256	A	V/V	(AVX512VL AVX512_VBMI) OR AVX10.1	Permute bytes in ymm3/m256 and ymm1 using byte indexes in ymm2 and store the byte results in ymm1 using writemask k1.
EVEX.512.66.0F38.W0 7D /r	VPERMT2B zmm1 {k1}{z}, zmm2, zmm3/m512	A	V/V	AVX512_VBMI OR AVX10.1	Permute bytes in zmm3/m512 and zmm1 using byte indexes in zmm2 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 from two tables, comprising of the first operand (also the destination operand) and the third operand (the second source operand). The second operand (the first source operand) provides byte indices to select byte results from the two tables. 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 second operand contains input indices to select elements from the two input tables in the 1st and 3rd operands. The first operand is also the destination of the result. The second source 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 second table and the indices can be reused in subsequent iterations, but the first table is overwritten. Bits (MAX_VL-1:256/128) of the destination are zeroed for VL=256,128. VPERMT2B—Full Permute of Bytes From Two Tables Overwriting a Table Vol. 2C 5-533

Operation

VPERMT2B (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] := SRC1[j*8+id+1]? SRC2[off+7:off] : TMP_DEST[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

VPERMT2B __m512i _mm512_permutex2var_epi8(__m512i a, __m512i idx, __m512i b);
VPERMT2B __m512i _mm512_mask_permutex2var_epi8(__m512i a, __mmask64 k, __m512i idx, __m512i b);
VPERMT2B __m512i _mm512_maskz_permutex2var_epi8(__mmask64 k, __m512i a, __m512i idx, __m512i b);
VPERMT2B __m256i _mm256_permutex2var_epi8(__m256i a, __m256i idx, __m256i b);
VPERMT2B __m256i _mm256_mask_permutex2var_epi8(__m256i a, __mmask32 k, __m256i idx, __m256i b);
VPERMT2B __m256i _mm256_maskz_permutex2var_epi8(__mmask32 k, __m256i a, __m256i idx, __m256i b);
VPERMT2B __m128i _mm_permutex2var_epi8(__m128i a, __m128i idx, __m128i b);
VPERMT2B __m128i _mm_mask_permutex2var_epi8(__m128i a, __mmask16 k, __m128i idx, __m128i b);
VPERMT2B __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.” VPERMT2B—Full Permute of Bytes From Two Tables Overwriting a Table Vol. 2C 5-534