# `stvrx` — Store Vector Right Indexed
> **Category:** [Memory](../categories/memory.md) · **Form:** [X](../forms/X.md) · **Opcode:** `0x7c00054e`
## Assembler Mnemonics
| Mnemonic | XML entry | Flags | Description |
| --- | --- | --- | --- |
| `stvrx` | `stvrx` | — | Store Vector Right Indexed |
| `stvrx128` | `stvrx128` | — | Store Vector Right Indexed 128 |
## Syntax
```asm
stvrx [VS], [RA0], [RB]
stvrx128 [VS], [RA0], [RB]
```
## Encoding
### `stvrx` — form `X`
- **Opcode word:** `0x7c00054e`
- **Primary opcode (bits 0–5):** `31`
- **Extended opcode:** `679`
- **Synchronising:** no
| Bits | Field | Meaning |
| --- | --- | --- |
| 0–5 | `OPCD` | primary opcode |
| 6–10 | `RT/FRT/VRT` | destination |
| 11–15 | `RA/FRA/VRA` | source A |
| 16–20 | `RB/FRB/VRB` | source B |
| 21–30 | `XO` | extended opcode (10 bits) |
| 31 | `Rc` | record-form flag |
### `stvrx128` — form `VX128_1`
- **Opcode word:** `0x10000543`
- **Primary opcode (bits 0–5):** `4`
- **Extended opcode:** `1347`
- **Synchronising:** no
| Bits | Field | Meaning |
| --- | --- | --- |
| 0–5 | `OPCD` | primary opcode (4) |
| 6–10 | `VD128l` | destination low 5 bits |
| 11–15 | `RA` | address register |
| 16–20 | `RB` | offset register |
| 21–27 | `XO` | extended opcode |
| 28–29 | `VD128h` | destination high 2 bits |
| 30–31 | `—` | reserved |
## Operands
| Field | Role | Description |
| --- | --- | --- |
| `VS` | stvrx: read; stvrx128: read | Source vector register (alias for VD on stores). |
| `RA0` | stvrx: read; stvrx128: read | Source GPR; when the encoded register number is 0 the operand is the literal 64-bit zero, **not** `r0`. |
| `RB` | stvrx: read; stvrx128: read | Source GPR. |
## Register Effects
### `stvrx`
- **Reads (always):** `VS`, `RA0`, `RB`
- **Reads (conditional):** _none_
- **Writes (always):** _none_
- **Writes (conditional):** _none_
### `stvrx128`
- **Reads (always):** `VS`, `RA0`, `RB`
- **Reads (conditional):** _none_
- **Writes (always):** _none_
- **Writes (conditional):** _none_
## Status-Register Effects
_No condition-register or status-register effects._
## Operation (pseudocode)
```
; Pseudocode derives directly from the xenia-rs interpreter
; arm (see Implementation References). Operation semantics:
; - Read source operands from the fields listed under Operands.
; - Apply the arithmetic / logical / memory action described
; in the Description field above.
; - Write results to the destination register(s); update any
; status bits enumerated under Status-Register Effects.
; Consult the IBM AIX reference link under IBM Reference for
; canonical PPC-style pseudocode where xenia's expression is
; terse.
```
## C Translation Example
```c
/* C translation: the xenia-rs interpreter arm below in */
/* Implementation References is the authoritative semantic */
/* snapshot. Translate it line-by-line: */
/* - ctx.gpr[N] -> r[N] (or f[]/v[] for FPRs/VRs) */
/* - mem.read_u*/write_u* -> mem_read_u*_be / mem_write_u*_be */
/* - ctx.update_cr_signed(fld, v) -> update_cr_signed(fld, v) */
/* - ctx.xer_ca / xer_ov / xer_so -> xer.CA / xer.OV / xer.SO */
/* The Register Effects and Status-Register Effects tables above */
/* enumerate every side effect a faithful translation must emit. */
```
## Implementation References
**`stvrx`**
- xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="stvrx"`](../../xenia-canary/tools/ppc-instructions.xml)
- xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_altivec.cc:290`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_altivec.cc#L290)
- xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:78`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L78)
- xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:833`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L833)
- xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:3134-3150`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L3134-L3150)
xenia-rs interpreter body (frozen snapshot)
```rust
PpcOpcode::stvrx | PpcOpcode::stvrxl => {
let ea = ea_indexed(ctx, instr);
// PPCBUG-514: stvrx/stvrxl were missing invalidate_for_write.
// store_vector_right writes [ea & !0xF, ea-1] (up to 15 bytes, all within a single
// 16-byte-aligned block). Two-call form is kept for defensive correctness.
// stvrx at shift==0 is a no-op; the guard fires unconditionally (cheap).
if let Some(t) = ctx.reservation_table.as_ref().filter(|t| t.is_enabled()) {
if t.has_active_reservers() {
let first_line = ea & !RESERVATION_MASK;
let last_line = ea.wrapping_add(15) & !RESERVATION_MASK;
t.invalidate_for_write(first_line);
if last_line != first_line { t.invalidate_for_write(last_line); }
}
}
crate::vmx::store_vector_right(mem, ea, ctx.vr[instr.rs()]);
ctx.pc += 4;
}
```
xenia-rs interpreter body (frozen snapshot)
```rust
PpcOpcode::stvrx128 | PpcOpcode::stvrxl128 => {
let ea = ea_indexed(ctx, instr);
// PPCBUG-514: stvrx128/stvrxl128 were missing invalidate_for_write.
if let Some(t) = ctx.reservation_table.as_ref().filter(|t| t.is_enabled()) {
if t.has_active_reservers() {
let first_line = ea & !RESERVATION_MASK;
let last_line = ea.wrapping_add(15) & !RESERVATION_MASK;
t.invalidate_for_write(first_line);
if last_line != first_line { t.invalidate_for_write(last_line); }
}
}
crate::vmx::store_vector_right(mem, ea, ctx.vr[instr.vs128()]);
ctx.pc += 4;
}
```