shll

Shift Left Long

SHLL <Vd>.<Td>, <Vn>.<Ts>, #<shift>

Shifts narrow vector left, extending to wide result.

Details

Shifts narrow SIMD vector elements left by an immediate amount and zero-extends them to twice the width, placing the results in a wider destination register. This is an AArch64-only NEON instruction that operates on 8, 16, or 32-bit integer elements and produces 16, 32, or 64-bit results respectively. Condition flags are not affected.

Pseudocode Operation

for i = 0 to (128 >> (size+1)) - 1 do
  operand ← ZeroExtend(Vn[i], element_width)
  Vd[i] ← operand << imm
end for

Example

SHLL v0.4s.Td, v1.4s.Ts, #LSL

Encoding

Binary Layout
0
Q
1
01110
size
10000
10011
10
Rn
Rd
 
Format SIMD Shift Imm
Opcode 0x2E213800
Extension NEON (SIMD)

Operands

  • Vd
    Dest (Wide)
  • Vn
    First source SIMD/FP vector register
  • shift
    Imm

Reference (Arm A64 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0x2E213800 SHLL{2} <Vd>.<Ta>, <Vn>.<Tb>, #<shift> A64 0 | Q | 1 | 01110 | size | 10000 | 10011 | 10 | Rn | Rd

Description

Shift Left Long (by element size). This instruction reads each vector element in the lower or upper half of the source SIMD&FP register, left shifts each result by the element size, writes the final result to a vector, and writes the vector to the destination SIMD&FP register. The destination vector elements are twice as long as the source vector elements. The SHLL instruction extracts vector elements from the lower half of the source register. The SHLL2 instruction extracts vector elements from the upper half of the source register. Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.

Operation

CheckFPAdvSIMDEnabled64();
bits(datasize) operand = Vpart[n, part, datasize];
bits(2*datasize) result;
integer element;

for e = 0 to elements-1
    element = Int(Elem[operand, e, esize], unsigned) << shift;
    Elem[result, e, 2*esize] = element<2*esize-1:0>;

V[d, 2*datasize] = result;