f3c512f2ab
The hand-written parts of the manual still described how the retired xenia-rs interpreter behaved: its snapshots, Rust casts and helpers. Each of those 490 statements is now either restated as what Canary's emitters and x64 backend actually do (at the pinned canary_experimental commit), or dropped where it only made sense for xenia-rs. Checking them turned up claims that were wrong, not just outdated: - VSCR[SAT] is never modelled in Canary (DID_SATURATE is a stub and mfvscr cannot see it); the pages said saturating ops set it stickily. - Canary does not implement lswi/lswx/stswi/stswx, dcbi, mtfsb0/mtfsb1, vmsum*, vmhaddshs, vupkhpx/vupklpx, and most SPRs; pages described them as working. - Traps evaluate TO in Canary; stvebx/stvehx/stvewx store one element, not 16 bytes; mtmsrd writes only EE; fres/frsqrte/vrsqrtefp precision claims and the stfs "rounds under RN / sets FPSCR" claim contradicted the spec. - Reservations are a 64 KiB block bitmap plus a value compare, not per-address tracking. Claims that neither Canary's source nor a public spec settles are marked unverified (NI at boot, vmaddcfp128 operand order, estimate bit-exactness). Generated regions are untouched; re-running the generator changes nothing. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
122 lines
5.2 KiB
Markdown
122 lines
5.2 KiB
Markdown
# `lswx` — Load String Word Indexed
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> **Category:** [Memory](../categories/memory.md) · **Form:** [X](../forms/X.md) · **Opcode:** `0x7c00042a`
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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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| `lswx` | `lswx` | — | Load String Word Indexed |
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## Syntax
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```asm
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(no disassembly template)
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```
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## Encoding
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### `lswx` — form `X`
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- **Opcode word:** `0x7c00042a`
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- **Primary opcode (bits 0–5):** `31`
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- **Extended opcode:** `533`
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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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## Register Effects
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### `lswx`
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- **Reads (always):** _none_
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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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; No hand-written pseudocode for this instruction yet.
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; The authoritative semantics are the Canary emitter snapshot under
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; Implementation References; about half of Canary's emitters open
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; with the PPC-style definition as a comment (`RD <- (RA) + (RB)`).
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; Every side effect is also enumerated in the Register Effects and
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; Status-Register Effects tables above.
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```
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## C Translation Example
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```c
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/* No hand-written C yet. Translate the Canary emitter snapshot */
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/* under Implementation References; its HIR maps directly: */
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/* f.LoadGPR(n) / f.StoreGPR(n, v) -> r[n] / r[n] = v */
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/* f.LoadFPR / StoreFPR, f.LoadVR / StoreVR -> f[n], v[n] */
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/* f.Load(ea, T), f.Store(ea, v) -> raw read / write; emitters */
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/* wrap them in f.ByteSwap for the big-endian guest value */
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/* f.UpdateCR(n, v) -> CR field n from v's LOW 32 BITS vs 0 */
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/* f.LoadCA / f.StoreCA -> xer.CA; f.StoreSAT -> vscr.SAT */
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/* i.XO.RA, i.D.DS, ... -> the bit-fields listed under Operands */
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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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**`lswx`**
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- Canary XML: [`tools/ppc-instructions.xml` — search for `mnem="lswx"`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/tools/ppc-instructions.xml)
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- Canary emitter: [`src/xenia/cpu/ppc/ppc_emit_memory.cc:732`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/src/xenia/cpu/ppc/ppc_emit_memory.cc#L732)
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- Sylpheed opcode: [`crates/sylpheed-ppc/src/opcode.rs:134`](../../../crates/sylpheed-ppc/src/opcode.rs#L134)
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- Sylpheed decoder: [`crates/sylpheed-ppc/src/decoder.rs:932`](../../../crates/sylpheed-ppc/src/decoder.rs#L932)
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<details><summary>Canary emitter (frozen snapshot @ <code>f21ebd49e9</code>)</summary>
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```cpp
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int InstrEmit_lswx(PPCHIRBuilder& f, const InstrData& i) {
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XEINSTRNOTIMPLEMENTED();
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return 1;
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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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- **Byte count from `XER[25..31]`.** Unlike `lswi` (where the count is encoded as `RB`), `lswx` reads `XER[25..31]` for the byte count `NB` (0..127). `NB = 0` is **not** the "32 bytes" special case here — zero means literally zero bytes, no registers touched. ⚠️ Canary does not implement `lswx`: its emitter is `XEINSTRNOTIMPLEMENTED`, so translating one logs "Unimplemented instr" and, with the default `break_on_unimplemented_instructions`, breaks.
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- **Register packing identical to `lswi`.** Bytes are packed big-endian into successive GPRs starting at `RT`, four bytes per register, with wraparound `r31 → r0`. Trailing bytes in the last register are zero-padded on the right.
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- **`RA0` semantics.** `RA = 0` selects literal zero. The instruction has no update form — `RA` is not modified.
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- **Invalid forms.** AIX flags as invalid: `RT` collides with `RA` or `RB` within the destination range; `XER[25..31]` and `NB` byte stream wraps around through both `RA` and `RB`. Canary does not implement `lswx` (`XEINSTRNOTIMPLEMENTED`).
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- **Used for non-multiple-of-4 copies.** Together with `lswi`, gives a way to load a runtime-determined byte count without per-byte loops. Compilers don't emit it; rare hand-written copy primitives may.
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- **Alignment.** Architecture allows arbitrary alignment; cache-inhibited storage may raise alignment exceptions on real hardware.
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- **No FPSCR / CR effects.** Pure data movement.
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## Related Instructions
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- [`lswi`](lswi.md) — sibling with byte count encoded as `RB` field (immediate-style).
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- [`stswx`](stswx.md), [`stswi`](stswi.md) — symmetric stores.
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- [`lmw`](lmw.md) — word-granular bulk load (no byte tail handling).
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- [`lwz`](lwz.md), [`lbz`](lbz.md) — scalar loads compilers actually emit.
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## IBM Reference
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- [AIX 7.3 — `lswx` (Load String Word Indexed)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-lswx-load-string-word-indexed-instruction)
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- `PowerISA v2.07B Book II` § "Load and Store String" for invalid-form rules and `XER` interaction.
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