sri

Shift Right and Insert

SRI <Vd>.<T>, <Vn>.<T>, #<shift>

Shifts source right and inserts into destination.

Pseudocode Operation

for i = 0 to elements-1 do
  shifted ← Vn[i] >> shift
  Vd[i] ← (Vd[i] & ~mask) | (shifted & mask)
endfor
where mask selects the lower (element_width - shift) bits

Example

SRI v0.4s.T, v1.4s.T, #LSL

Encoding

Binary Layout

011110

28:23

immh

22:19

immb

18:16

01000

15:11

9:5

4:0

Format SIMD Shift Imm

Opcode 0x2F004400

Extension NEON (SIMD)

Operands

Vd
Destination SIMD/FP vector register
Vn
First source SIMD/FP vector register
shift
Imm

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction	ISA	Bit pattern
0x7F404400	SRI D<d>, D<n>, #<shift>	A64	01 \| 1 \| 111110 \| immh \| immb \| 01000 \| 1 \| Rn \| Rd
0x2F004400	SRI <Vd>.<T>, <Vn>.<T>, #<shift>	A64	0 \| Q \| 1 \| 011110 \| immh \| immb \| 01000 \| 1 \| Rn \| Rd
0x4500F000	SRI <Zd>.<T>, <Zn>.<T>, #<const>	A64	01000101 \| tszh \| 0 \| tszl \| imm3 \| 11110 \| 0 \| Zn \| Zd

Description

Shift Right and Insert (immediate). This instruction reads each vector element in the source SIMD&FP register, right shifts each vector element by an immediate value, and inserts the result into the corresponding vector element in the destination SIMD&FP register such that the new zero bits created by the shift are not inserted but retain their existing value. Bits shifted out of the right of each vector element of the source register are lost. 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 = V[n, datasize];
bits(datasize) operand2 = V[d, datasize];
bits(datasize) result;
bits(esize) mask = LSR(Ones(esize), shift);
bits(esize) shifted;

for e = 0 to elements-1
    shifted = LSR(Elem[operand, e, esize], shift);
    Elem[result, e, esize] = (Elem[operand2, e, esize] AND NOT(mask)) OR shifted;
V[d, datasize] = result;

sri