vqrshl

Vector Saturating Rounding Shift Left

VQRSHL<c>.<dt> <Qd>, <Qm>, <Qn>

Shifts left with saturation and rounding.

Pseudocode Operation

for i = 0 to elements-1 do
  shift_amount ← SignExtend(Qn[i])
  if shift_amount >= 0 then
    result ← SatQ(Qm[i] << shift_amount, esize)
  else
    rounding_bit ← Qm[i][(-shift_amount-1)]
    shifted ← Qm[i] >> (-shift_amount)
    result ← SatQ(shifted + rounding_bit, esize)
  Qd[i] ← result

Example

VQRSHL.dt q0, q2, q1

Encoding

Binary Layout

1111001

31:25

U

24

0

23

D

22

size

21:20

Vn

19:16

Vd

15:12

0101

11:8

N

7

0

6

M

5

1

4

Vm

3:0

 

Format NEON 3-Reg

Opcode 0xF2000510

Extension NEON (SIMD)

Operands

• Qd
  Destination 128-bit SIMD register
• Qm
  Second source 128-bit SIMD register
• Qn
  Shift Reg

Related

More in NEON (SIMD)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0xF2000510	VQRSHL{<c>}{<q>}.<dt> {<Dd>,} <Dm>, <Dn>		A32		1111001 | U | 0 | D | size | Vn | Vd | 0101 | N | 0 | M | 1 | Vm
0xF2000550	VQRSHL{<c>}{<q>}.<dt> {<Qd>,} <Qm>, <Qn>		A32		1111001 | U | 0 | D | size | Vn | Vd | 0101 | N | 1 | M | 1 | Vm
0xEF000510	VQRSHL{<c>}{<q>}.<dt> {<Dd>,} <Dm>, <Dn>		T32		111 | U | 11110 | D | size | Vn | Vd | 0101 | N | 0 | M | 1 | Vm
0xEF000550	VQRSHL{<c>}{<q>}.<dt> {<Qd>,} <Qm>, <Qn>		T32		111 | U | 11110 | D | size | Vn | Vd | 0101 | N | 1 | M | 1 | Vm

Description

Vector Saturating Rounding Shift Left takes each element in a vector, shifts them by a value from the least significant byte of the corresponding element of a second vector, and places the results in the destination vector. If the shift value is positive, the operation is a left shift. Otherwise, it is a right shift. For truncated results see VQSHL (register). The first operand and result elements are the same data type, and can be any one of: The second operand is a signed integer of the same size. If any of the results overflow, they are saturated. The cumulative saturation bit, FPSCR.QC, is set if saturation occurs. For details see Pseudocode details of saturation. 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(esize) result;
    boolean sat;
    for r = 0 to regs-1
        for e = 0 to elements-1
            integer element = Int(Elem[D[m+r], e, esize], unsigned);
            integer shift = SInt(Elem[D[n+r], e, esize]<7:0>);
            if shift >= 0 then // left shift
                element = element << shift;
            else               // rounding right shift
                shift = -shift;
                element = (element + (1 << (shift - 1))) >> shift;
            (result, sat) = SatQ(element, esize, unsigned);
            Elem[D[d+r], e, esize] = result;
            if sat then FPSCR.QC = '1';