All instructionsx86-64Shift

PSLLW

/ VPSLLW

Shift 16-bit elements left

Shift each 16-bit element left, filling the vacated low bits with zeros.

SSE216-bit unsigned elements

Similar operations on Arm64:SHLvshlq_n_u16

Instruction forms

3 in this sample
FormBitsRequiresEncoding
PSLLW xmm, imm8128SSE266 0F 71 /6 ib
VPSLLW xmm1, xmm2, imm8128AVXVEX.L0.66.0F.WIG 71 /6 ib
VPSLLW ymm1, ymm2, imm8256AVX2VEX.L1.66.0F.WIG 71 /6 ib
128 bits · 8 × 16-bit elements

Explore the operation

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Operation

Pseudo-C · selected form
dst[i] = count >= 16 ? 0 : (a[i] << count) & 0xffff

Simplified pseudocode for the selected form.

Exact upstream semantics

Standard variant

Source: intel/PSLLW-PSLLD-PSLLQ-Shift-Packed-Data-Left-Logical.xml/0

let elements := register_size / element_size;
var result := Zero(register_size);
for i := 0 to elements-1 do
let op1 := src1[i *: element_size];
let count := if shift_size > 64 then Unsigned(shift_distance[0 +: 64]) else Unsigned(shift_distance);
let r := Shift_Left_Logical(op1, count);
result[i *: element_size] := r;
endfor;

Parameterized by register and element size; from the pinned upstream definition.

What to watch for

  • This sample covers immediate-count forms.
  • Counts of 16 or more produce zero; the count is not reduced modulo 16.

Corresponding intrinsics

C / C++ · selected form
_mm_slli_epi16
__m128i _mm_slli_epi16(__m128i a, int imm8)
#include <emmintrin.h>SSE2

Documented instruction mapping; a compiler may use an equivalent encoding or optimize the operation away.

Documented mapping

PSLLW xmm, imm8

Architectural details

Flags
Arithmetic flags unchanged.
Destination
Writes the low 128 bits; upper vector-register bits are preserved.
Encoding
66 0F 71 /6 ib
Operands
  • xmmread / write · 128 bits (8 × 16) · unsigned
  • imm8read · 8 bits · unsigned
Coverage
Selected register-only 128/256-bit forms. Memory operands, MMX, and EVEX/AVX-512 forms are outside this sample.
Immediate
0 to 255.
Exception information & execution requirements
  • #NM
  • #UD

Feature availability alone does not guarantee execution: OS state and execution-level controls also apply. Use the linked architecture documentation for the full exception conditions.

Performance measurements are not included in this preview. Latency and throughput depend on the exact form and microarchitecture. Measured data on uops.info ↗

Sources & provenance

Technical fields are imported from pinned upstream files. Explanations and explorer behavior are maintained separately.

Intel · PSLLW-PSLLD-PSLLQ-Shift-Packed-Data-Left-Logical.xml
Revision
4ebe7f0ac1bd00f46244c49bb72c503ce368def7
SHA-256
1b97a06d6b6465e9097612b236f90f80836c2c21962e151c4d0917b951255819
Terms
Intel SDM terms; see License.md
View pinned upstream file ↗
Intel · intrinsics.xml
Revision
4ebe7f0ac1bd00f46244c49bb72c503ce368def7
SHA-256
6762a50652a35ef663fd532ed83b789d19bbc2ac7e94b1771f19d666d96c2c30
Terms
Intel SDM terms; see License.md
View pinned upstream file ↗

Intel sources are a documentation preview. Arm ACLE mappings are adapted under CC BY-SA 4.0 with an additional patent license. Arm MRS encoding data is distributed under BSD-3-Clause. © Arm Limited and contributors. Coverage and attribution.