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 Checking them turned up claims that were wrong, not just outdated: - VSCR[SAT] is never modelled in Canary (DID_SATURATE is a stub and mfvscr cannot see it); the pages said saturating ops set it stickily.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>
136 lines
5.4 KiB
Markdown
136 lines
5.4 KiB
Markdown
# `creqv` — Condition Register Equivalent
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> **Category:** [Control / CR / SPR](../categories/control.md) · **Form:** [XL](../forms/XL.md) · **Opcode:** `0x4c000242`
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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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| `creqv` | `creqv` | — | Condition Register Equivalent |
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## Syntax
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```asm
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creqv [CRBD], [CRBA], [CRBB]
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```
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## Encoding
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### `creqv` — form `XL`
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- **Opcode word:** `0x4c000242`
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- **Primary opcode (bits 0–5):** `19`
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- **Extended opcode:** `289`
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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 (19) |
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| 6–10 | `BT/BO` | target / branch options |
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| 11–15 | `BA/BI` | source A / CR bit to test |
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| 16–20 | `BB` | source B |
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| 21–30 | `XO` | extended opcode (10 bits) |
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| 31 | `LK` | link flag |
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## Operands
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| Field | Role | Description |
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| --- | --- | --- |
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| `CRBA` | creqv: read | CR source bit A (0–31). |
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| `CRBB` | creqv: read | CR source bit B (0–31). |
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| `CRBD` | creqv: write | CR destination bit (0–31). |
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## Register Effects
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### `creqv`
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- **Reads (always):** `CRBA`, `CRBB`
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- **Reads (conditional):** _none_
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- **Writes (always):** `CRBD`
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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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**`creqv`**
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- Canary XML: [`tools/ppc-instructions.xml` — search for `mnem="creqv"`](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_control.cc:370`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/src/xenia/cpu/ppc/ppc_emit_control.cc#L370)
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- Sylpheed opcode: [`crates/sylpheed-ppc/src/opcode.rs:37`](../../../crates/sylpheed-ppc/src/opcode.rs#L37)
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- Sylpheed decoder: [`crates/sylpheed-ppc/src/decoder.rs:833`](../../../crates/sylpheed-ppc/src/decoder.rs#L833)
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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_creqv(PPCHIRBuilder& f, const InstrData& i) {
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// CR[bt] <- CR[ba] == CR[bb] bt=bo, ba=bi, bb=bb
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Value* ba = f.LoadCRField(i.XL.BI >> 2, i.XL.BI & 3);
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Value* bb = f.LoadCRField(i.XL.BB >> 2, i.XL.BB & 3);
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Value* bt = f.CompareEQ(ba, bb);
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f.StoreCRField(i.XL.BO >> 2, i.XL.BO & 3, bt);
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return 0;
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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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- **Operation.** `CR[CRBD] ← ¬(CR[CRBA] XOR CR[CRBB])` — i.e. logical equivalence (XNOR). Result is 1 iff `CRBA` and `CRBB` agree.
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- **`crset BT` idiom.** With identical operands, `creqv BT, BT, BT` always yields 1 (any bit XNOR'd with itself is 1). This is the canonical PowerPC **set-to-1** for a single CR bit; assemblers recognise the simplified mnemonic `crset BT`.
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- **Bit-level operands.** Like all CR-logical ops, the three operands are 5-bit absolute CR-bit indices (0..31). Mixing CR fields is fine.
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- **Use case.** Branch on "A == B" of two prior compare results. Example: `crxor` of CR0.SO and CR1.SO gives "differ"; `creqv` gives "agree".
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- **No `Rc` / `OE`.** Doesn't touch CR0, XER, or any other state beyond the named bit.
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- **Not synchronising.** Reorderable.
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- **Canary status.** Canary emits the host equality compare of the two bits (XNOR). The `crset` simplified form is the most common occurrence in real Xbox 360 code.
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## Related Instructions
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- [`crand`](crand.md), [`crandc`](crandc.md) — AND family.
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- [`cror`](cror.md), [`crorc`](crorc.md), [`crnor`](crnor.md), [`crnand`](crnand.md) — OR family.
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- [`crxor`](crxor.md) — the dual; `crxor BT, BT, BT` is the standard **clear-to-0** idiom.
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- [`mcrf`](mcrf.md) — bulk CR-field move.
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- [`bcx`](../branch/bcx.md) — consumes the synthesised bit.
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### Simplified Mnemonics
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| Simplified | Expansion | Effect |
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| --- | --- | --- |
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| `crset BT` | `creqv BT, BT, BT` | force `CR[BT] ← 1` |
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## IBM Reference
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- [AIX 7.3 — `creqv` (Condition Register Equivalent)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-creqv-condition-register-equivalent-instruction)
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- [AIX 7.3 — Condition register simplified mnemonics](https://www.ibm.com/docs/en/aix/7.3.0?topic=mnemonics-condition-register-logical-simplified)
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