vrev16

Vector Reverse 16

VREV16<c>.<dt> <Qd>, <Qm>

Reverses bytes within 16-bit halfwords.

Details

Reverses the byte order within each 16-bit halfword element in the source register. For example, bytes [1,0] become [0,1] within each 16-bit element. Condition flags (N, Z, C, V) are not affected. Executes in A32/T32 with NEON extension; operates on integer data types.

Pseudocode Operation

for i = 0 to 127 by 16:
  for j = 0 to 15 by 8:
    Qd[i+j+7:i+j] ← Qm[i+15-j:i+8-j]

Example

VREV16.dt q0, q2

Encoding

Binary Layout
111100111
D
11
size
00
Vd
0
00
10
0
M
0
Vm
 
Format NEON 2-Reg
Opcode 0xF3B00100
Extension NEON (SIMD)

Operands

  • Qd
    Destination 128-bit SIMD register
  • Qm
    Second source 128-bit SIMD register

Reference (Arm AArch32 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0xF3B00100 VREV16{<c>}{<q>}.<dt> <Dd>, <Dm> A32 111100111 | D | 11 | size | 00 | Vd | 0 | 00 | 10 | 0 | M | 0 | Vm
0xF3B00140 VREV16{<c>}{<q>}.<dt> <Qd>, <Qm> A32 111100111 | D | 11 | size | 00 | Vd | 0 | 00 | 10 | 1 | M | 0 | Vm
0xFFB00100 VREV16{<c>}{<q>}.<dt> <Dd>, <Dm> T32 111111111 | D | 11 | size | 00 | Vd | 0 | 00 | 10 | 0 | M | 0 | Vm
0xFFB00140 VREV16{<c>}{<q>}.<dt> <Qd>, <Qm> T32 111111111 | D | 11 | size | 00 | Vd | 0 | 00 | 10 | 1 | M | 0 | Vm

Description

Vector Reverse in halfwords reverses the order of 8-bit elements in each halfword of the vector, and places the result in the corresponding destination vector. There is no distinction between data types, other than size. Depending on settings in the CPACR, NSACR, and HCPTR registers, and the Security state and PE mode in which the instruction is executed, an attempt to execute the instruction might be undefined, or trapped to Hyp mode. For more information see Enabling Advanced SIMD and floating-point support.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();  CheckAdvSIMDEnabled();

    bits(64) result;
    integer element;
    integer rev_element;
    for r = 0 to regs-1
        element = 0;
        for c = 0 to containers-1
            rev_element = (element + elements_per_container) - 1;
            for e = 0 to elements_per_container-1
                Elem[result, rev_element, esize] = Elem[D[m+r], element, esize];
                element = element + 1;
                rev_element = rev_element - 1;
        D[d+r] = result;