vpermb

Permute Packed Bytes

VPERMB zmm1 {k1}, zmm2, zmm3/m512

Permutes bytes in ZMM based on index vector.

Details

Permutes bytes within 64-byte blocks of a ZMM register using a 512-bit index vector; each byte in the index selects a source byte (bits 3–0 select lane, bits 6–4 select byte within 64-byte lane). Requires AVX-512-VBMI. Supports write-masking via {k1}. No flags are affected.

Pseudocode Operation

for lane = 0 to 7:
  for byte_in_lane = 0 to 63:
    idx_byte = zmm2[lane*64 + byte_in_lane]
    src_lane = idx_byte & 0x7
    src_byte_offset = idx_byte >> 3
    if src_byte_offset < 64:
      selected = zmm3[src_lane*64 + src_byte_offset]
    else:
      selected = 0
    if k1[byte_in_lane] or k1 is not used:
      zmm1[lane*64 + byte_in_lane] ← selected

Example

VPERMB zmm1, zmm2, zmm3/m512

Encoding

Binary Layout

EVEX

Format EVEX

Opcode EVEX.512.66.0F38.W0 8D /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 8D /r	VPERMB xmm1 {k1}{z}, xmm2, xmm3/m128	A	V/V	(AVX512VL AND AVX512_VBMI) OR AVX10.1	Permute bytes in xmm3/m128 using byte indexes in xmm2 and store the result in xmm1 using writemask k1.
EVEX.256.66.0F38.W0 8D /r	VPERMB ymm1 {k1}{z}, ymm2, ymm3/m256	A	V/V	AVX512VL AVX512_VBMI) OR AVX10.1	Permute bytes in ymm3/m256 using byte indexes in ymm2 and store the result in ymm1 using writemask k1.
EVEX.512.66.0F38.W0 8D /r	VPERMB zmm1 {k1}{z}, zmm2, zmm3/m512	A	V/V	AVX512_VBMI OR AVX10.1	Permute bytes in zmm3/m512 using byte indexes in zmm2 and store the result 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 (w)	EVEX.vvvv (r)	ModRM:r/m (r)	N/A

Description

Copies bytes from the second source operand (the third operand) to the destination operand (the first operand) according to the byte indices in the first source operand (the second operand). Note that this instruction permits a byte in the source operand to be copied to more than one location in the destination operand. Only the low 6(EVEX.512)/5(EVEX.256)/4(EVEX.128) bits of each byte index is used to select the location of the source byte from the second source operand. The first source operand is a ZMM/YMM/XMM register. The second source operand can be a ZMM/YMM/XMM register, a 512/256/128-bit memory location. The destination operand is a ZMM/YMM/XMM register updated at byte granularity by the writemask k1.

Operation

VPERMB (EVEX encoded versions)
(KL, VL) = (16, 128), (32, 256), (64, 512)
IF VL = 128:
n := 3;
ELSE IF VL = 256:
n := 4;
ELSE IF VL = 512:
n := 5;
FI;
FOR j := 0 TO KL-1:
id := SRC1[j*8 + n : j*8] ; // location of the source byte
IF k1[j] OR *no writemask* THEN
DEST[j*8 + 7: j*8] := SRC2[id*8 +7: id*8];
ELSE IF zeroing-masking THEN
DEST[j*8 + 7: j*8] := 0;
*ELSE
DEST[j*8 + 7: j*8] remains unchanged*
FI
ENDFOR
DEST[MAX_VL-1:VL] := 0;





VPERMB—Permute Packed Bytes Elements                                                                                                      Vol. 2C 5-498

Intel C/C++ Compiler Intrinsic Equivalent

VPERMB __m512i _mm512_permutexvar_epi8( __m512i idx, __m512i a);
VPERMB __m512i _mm512_mask_permutexvar_epi8(__m512i s, __mmask64 k, __m512i idx, __m512i a);
VPERMB __m512i _mm512_maskz_permutexvar_epi8( __mmask64 k, __m512i idx, __m512i a);
VPERMB __m256i _mm256_permutexvar_epi8( __m256i idx, __m256i a);
VPERMB __m256i _mm256_mask_permutexvar_epi8(__m256i s, __mmask32 k, __m256i idx, __m256i a);
VPERMB __m256i _mm256_maskz_permutexvar_epi8( __mmask32 k, __m256i idx, __m256i a);
VPERMB __m128i _mm_permutexvar_epi8( __m128i idx, __m128i a);
VPERMB __m128i _mm_mask_permutexvar_epi8(__m128i s, __mmask16 k, __m128i idx, __m128i a);
VPERMB __m128i _mm_maskz_permutexvar_epi8( __mmask16 k, __m128i idx, __m128i a);

Exceptions

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Exceptions Type E4NF.nb in Table 2-52, “Type E4NF Class Exception Conditions.” VPERMB—Permute Packed Bytes Elements Vol. 2C 5-499