RVOPcode
Home/Instructions/VSSRA-VI
VSSRA.VI

RISC-V VSSRA.VI Instruction Details

Instruction ManualI-type

VSSRA.VI performs an element-wise fixed-point rounding arithmetic right shift using a shift count from the 5-bit unsigned uimm.

Instruction Syntax

vssra.vi vd, vs2, uimm, vm
Operand Breakdown
vs3: source vector register group providing active elements to store.
rs1: integer base-address register; unit-stride forms write consecutive addresses.
vm: when present, vm=0 uses v0 as the execution mask and vm=1 is unmasked.
VVector Operations
Related Search Terms
VSSRA.VI instructionvssra.vi syntaxvssra.vi encodingRVV scaling shiftvxrm roundingarithmetic right shift

Instruction Behavior

VSSRA.VI is a RISC-V V extension fixed-point scaling shift. It reads active vs2 elements, uses the low shift-count bits from the 5-bit unsigned uimm, rounds shifted-out bits according to vxrm, and writes the SEW-width result to vd.

VSSRA.VI Decode And Execute Animation

Starts from OP-V encoding fields, then shows how VSSRA takes the low shift-count bits, rounds with vxrm, and preserves sign through arithmetic right shift.

Instruction input
vssra.vi
immediate value
4 -> shamt 4
5-bit unsigned uimm; shift count uses low lg2(SEW) bits
OP-V encodingvssra.vi
funct6
101011
vm
0
vs2
01000
uimm
00100
funct3
011
vd
00100
opcode
1010111
lane
0
1
2
3
4
5
6
7
v8
0x0035
0x800c
0x0080
0x0123
0x801b
0x0019
0x0035
0x802a
round>>
round>>
round>>
round>>
round>>
round>>
round>>
round>>
imm
0x0004
0x0004
0x0004
0x0004
0x0004
0x0004
0x0004
0x0004
v0.t
1
0
1
1
1
0
1
1
v4
...
-
...
...
...
-
...
...
Current step

Show OP-V 32-bit encoding fields

vssra.vi uses OP-V encoding. The animation places fixed fields, register fields, vm, and the uimm field in one encoding strip.

This animation shows only ISA-visible relationships from the official V extension: OP-V field decode, active-element reads, SEW-width integer scaling arithmetic right shift, vxrm fixed-point rounding, and vd writeback. It does not model pipelines, caches, or timing.

Quick Understanding & Search Notes

VSSRA.VI is an RVV fixed-point scaling operation: active lanes take values from vs2, take the shift count from the 5-bit unsigned uimm, apply vxrm rounding, and write vd.

Official syntax is `vssra.vi vd, vs2, uimm, vm`; vm selects unmasked execution or v0.t masking.
VSSRA uses the V extension fixed-point rounding-mode CSR vxrm, with rnu, rne, rdn, and rod modes.
The arithmetic right-shift result is written at SEW width; inactive elements follow the current vtype mask/tail policy.
VSSRA does not set vxsat, unlike the saturating narrowing behavior of VNCLIP/VNCLIPU.
RISC-V Unprivileged ISA Manual: V Standard Extension for Vector Operations

Vector Execution Context

When reading VSSRA.VI, do not stop at the mnemonic. Official V-extension semantics also depend on the current vl, vtype, and mask state. .vi: one vector source and a small immediate participate.

Check vl first

The current vl determines the number of body elements. Typical code executes vsetvli, vsetivli, or vsetvl before this instruction.

Then check vtype

The current vtype supplies SEW, LMUL, tail policy, and mask policy; these affect element width, register-group size, and inactive/tail destination elements.

Then check vm/v0

For ordinary vector instructions with vm, vm=0 uses v0 as the execution mask and vm=1 is unmasked. A few forms such as VMERGE use v0 as data-selection input.

Official source: RISC-V V Standard Extension for Vector Operations

Common Usage Scenarios

Fixed-point scaling

Understand this scenario with real code like «vssra.vi v8, v12, 3, v0.t».

Vector shifts

Understand this scenario with real code like «vssra.vi v8, v12, 3, v0.t».

DSP data paths

Understand this scenario with real code like «vssra.vi v8, v12, 3, v0.t».

Pre-Use Checklist

Syntax Check
  • Confirm the current instruction format is I-type.
  • Confirm the operand order matches the example.
Semantic Check
  • Ensure the destination register usage is compatible with the calling convention.
  • Confirm this is not the lower-level form of a pseudo-instruction expansion.

Pitfalls / Common Confusions

VSSRA rounds shifted-out bits with vxrm; it is not an ordinary VSRA right shift.
The instruction does not saturate or set vxsat; use VNCLIP/VNCLIPU for saturating narrowing shifts.
The VI form uses a 5-bit unsigned immediate; the effective shift count still uses the SEW-selected low bits.

FAQ

How is VSSRA.VI different from VSRA?

VSSRA.VI rounds shifted-out bits according to vxrm during the right shift; VSRA is an ordinary right shift and does not use vxrm.

Does VSSRA.VI set vxsat?

No. VSSRA.VI is a fixed-point rounding scaling shift, not a saturating clip instruction.