e6d43a23ac
Bundles state that lives OUTSIDE the xenia-rs repo so a fresh clone on
another machine can be brought up to identical configuration via
migration/setup.sh:
- claude-memory/ ~/.claude/projects/-home-fabi-RE-Project-Sylpheed/memory/
(103 files, 1.1 MB - MEMORY.md + every
project_xenia_rs_*.md from audits
addis_signext through audit-058)
- project-root/dot-claude/ <project-root>/.claude/settings.json
(Stop hook + permissions)
- project-root/ppc-manual/ <project-root>/ppc-manual/
(PowerPC reference docs, 397 files, 3.7 MB)
- project-root/run-canary.sh <project-root>/run-canary.sh
- README.md Human-readable setup checklist
- setup.sh Idempotent installer (also reclones
xenia-canary at pinned HEAD 6de80dffe)
- MANIFEST.md Per-file mapping + per-file-not-bundled
restoration recipe
Excluded from bundle (not shippable via git):
- Sylpheed ISO (7.8 GB; copyright; manual copy required)
- sylpheed.db (395 MB; regenerable from XEX via analysis tooling)
- target/ build artifacts (rebuild on target)
- audit-runs probe firehoses (.log/.stdout/.stderr ~11 GB; rerun if needed)
- audit-runs memory dumps (.bin ~4.5 GB; rerun audit-026/027/029 if needed)
- xenia-canary checkout (setup.sh reclones from
git.mc02.dev/fabi/Xenia-Canary.git at HEAD 6de80dffe)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
132 lines
5.2 KiB
Markdown
132 lines
5.2 KiB
Markdown
# `sthbrx` — Store Half Word Byte-Reverse Indexed
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> **Category:** [Memory](../categories/memory.md) · **Form:** [X](../forms/X.md) · **Opcode:** `0x7c00072c`
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<!-- GENERATED: BEGIN -->
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## Assembler Mnemonics
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| Mnemonic | XML entry | Flags | Description |
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| --- | --- | --- | --- |
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| `sthbrx` | `sthbrx` | — | Store Half Word Byte-Reverse Indexed |
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## Syntax
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```asm
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sthbrx [RS], [RA0], [RB]
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```
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## Encoding
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### `sthbrx` — form `X`
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- **Opcode word:** `0x7c00072c`
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- **Primary opcode (bits 0–5):** `31`
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- **Extended opcode:** `918`
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- **Synchronising:** no
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| Bits | Field | Meaning |
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| --- | --- | --- |
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| 0–5 | `OPCD` | primary opcode |
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| 6–10 | `RT/FRT/VRT` | destination |
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| 11–15 | `RA/FRA/VRA` | source A |
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| 16–20 | `RB/FRB/VRB` | source B |
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| 21–30 | `XO` | extended opcode (10 bits) |
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| 31 | `Rc` | record-form flag |
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## Operands
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| Field | Role | Description |
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| --- | --- | --- |
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| `RS` | sthbrx: read | Source GPR (alias for RD in some stores). |
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| `RA0` | sthbrx: read | Source GPR; when the encoded register number is 0 the operand is the literal 64-bit zero, **not** `r0`. |
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| `RB` | sthbrx: read | Source GPR. |
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## Register Effects
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### `sthbrx`
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- **Reads (always):** `RS`, `RA0`, `RB`
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- **Reads (conditional):** _none_
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- **Writes (always):** _none_
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- **Writes (conditional):** _none_
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## Status-Register Effects
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_No condition-register or status-register effects._
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## Operation (pseudocode)
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```
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; Pseudocode derives directly from the xenia-rs interpreter
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; arm (see Implementation References). Operation semantics:
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; - Read source operands from the fields listed under Operands.
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; - Apply the arithmetic / logical / memory action described
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; in the Description field above.
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; - Write results to the destination register(s); update any
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; status bits enumerated under Status-Register Effects.
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; Consult the IBM AIX reference link under IBM Reference for
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; canonical PPC-style pseudocode where xenia's expression is
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; terse.
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```
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## C Translation Example
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```c
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/* C translation: the xenia-rs interpreter arm below in */
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/* Implementation References is the authoritative semantic */
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/* snapshot. Translate it line-by-line: */
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/* - ctx.gpr[N] -> r[N] (or f[]/v[] for FPRs/VRs) */
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/* - mem.read_u*/write_u* -> mem_read_u*_be / mem_write_u*_be */
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/* - ctx.update_cr_signed(fld, v) -> update_cr_signed(fld, v) */
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/* - ctx.xer_ca / xer_ov / xer_so -> xer.CA / xer.OV / xer.SO */
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/* The Register Effects and Status-Register Effects tables above */
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/* enumerate every side effect a faithful translation must emit. */
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```
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## Implementation References
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**`sthbrx`**
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- xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="sthbrx"`](../../xenia-canary/tools/ppc-instructions.xml)
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- xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_memory.cc:667`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_memory.cc#L667)
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- xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:73`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L73)
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- xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:846`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L846)
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- xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:1822-1830`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L1822-L1830)
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<details><summary>xenia-rs interpreter body (frozen snapshot)</summary>
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```rust
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PpcOpcode::sthbrx => {
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let ea = if instr.ra() == 0 { 0u64 } else { ctx.gpr[instr.ra()] };
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let ea = ea.wrapping_add(ctx.gpr[instr.rb()]) as u32;
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if let Some(t) = ctx.reservation_table.as_ref().filter(|t| t.is_enabled()) {
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if t.has_active_reservers() { t.invalidate_for_write(ea); }
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}
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mem.write_u16(ea, (ctx.gpr[instr.rs()] as u16).swap_bytes());
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ctx.pc += 4;
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}
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```
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</details>
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<!-- GENERATED: END -->
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## Special Cases & Edge Conditions
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- **Writes little-endian half.** Takes the low 16 bits of `RS`, swaps the two bytes, writes them at `EA`. After execution, byte at `EA` is `RS[56:63]` (low byte) and byte at `EA+1` is `RS[48:55]` (high byte). The xenia snapshot does `(ctx.gpr[instr.rs()] as u16).swap_bytes()`.
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- **Used to emit little-endian half-words.** Symmetric counterpart of [`lhbrx`](lhbrx.md). Common in PNG / ZIP / RIFF chunk emit paths.
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- **High bits of `RS` ignored.** Storing a 64-bit value through `sthbrx` truncates and reverses only the low half-word; the high 48 bits are not consulted.
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- **X-form only — no D-form, no update form.** Only the indexed form exists. `EA = (RA|0) + RB`.
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- **`RA0` semantics.** When `RA = 0`, base is literal zero; `sthbrx RS, 0, RB` writes at exact `RB`.
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- **Alignment.** Hardware tolerates unaligned half-word writes; cache-inhibited storage may raise alignment exceptions on real hardware.
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- **No CR / FPSCR effects.**
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## Related Instructions
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- [`lhbrx`](lhbrx.md) — load-half byte-reverse (matching load).
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- [`stwbrx`](stwbrx.md), [`stdbrx`](stdbrx.md) — wider byte-reverse stores.
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- [`sth`](sth.md), [`sthx`](sth.md) — non-reversing half stores.
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## IBM Reference
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- [AIX 7.3 — `sthbrx` (Store Half Byte-Reverse Indexed)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-sthbrx-store-half-byte-reverse-indexed-instruction)
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- `PowerISA v2.07B Book II` § "Byte-Reverse Storage Access".
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