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>
133 lines
5.7 KiB
Markdown
133 lines
5.7 KiB
Markdown
# `mffsx` — Move from FPSCR
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> **Category:** [Control / CR / SPR](../categories/control.md) · **Form:** [X](../forms/X.md) · **Opcode:** `0xfc00048e`
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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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| `mffs` | `mffsx` | — | Move from FPSCR |
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| `mffs.` | `mffsx` | Rc=1 | Move from FPSCR |
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## Syntax
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```asm
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mffs[Rc] [RD]
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```
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## Encoding
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### `mffsx` — form `X`
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- **Opcode word:** `0xfc00048e`
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- **Primary opcode (bits 0–5):** `63`
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- **Extended opcode:** `583`
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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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| `FPSCR` | mffsx: read | Floating-Point Status and Control Register. |
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| `FD` | mffsx: write | Destination floating-point register. |
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| `CR` | mffsx: write (conditional) | Condition-register update. When `Rc=1`, CR field 0 (or CR6 for vector compares, CR1 for FPU) is updated from the result. |
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## Register Effects
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### `mffsx`
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- **Reads (always):** `FPSCR`
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- **Reads (conditional):** _none_
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- **Writes (always):** `FD`
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- **Writes (conditional):** `CR`
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## Status-Register Effects
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- `mffsx`: **CR0** ← signed-compare(result, 0) with `SO ← XER[SO]`, when `Rc=1`.
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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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**`mffsx`**
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- xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="mffsx"`](../../xenia-canary/tools/ppc-instructions.xml)
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- xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_fpu.cc:397`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_fpu.cc#L397)
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- xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:53`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L53)
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- xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:910`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L910)
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- xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:3035-3040`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L3035-L3040)
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<details><summary>xenia-rs interpreter body (frozen snapshot)</summary>
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```rust
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PpcOpcode::mffsx => {
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// Move from FPSCR: frD = FPSCR as double (low 32 bits)
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ctx.fpr[instr.rd()] = f64::from_bits(ctx.fpscr as u64);
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if instr.rc_bit() { update_cr1_from_fpscr(ctx); }
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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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- **Operation.** Reads the 32-bit FPSCR and places it in the **low 32 bits** of `FRT`. The high 32 bits of the destination FPR are architecturally undefined; xenia leaves them as the bit-pattern of the FPSCR cast to `u64` (i.e. the high bits are zero, since FPSCR is 32-bit). PowerISA explicitly permits implementations to leave anything there.
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- **Destination is an FPR, not a GPR.** Use [`stfd`](../memory/stfd.md) to spill the FPR to memory and reload via a GPR if the value is needed in the integer file.
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- **`mffs.` (`Rc=1`) updates CR1.** The `Rc` bit copies the high four FPSCR bits (FX, FEX, VX, OX) into CR1's LT/GT/EQ/SO. xenia-rs implements this via `update_cr1_from_fpscr`.
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- **No FPSCR side effect.** Pure read; FPSCR is not modified (unlike [`mcrfs`](mcrfs.md), which clears sticky exception bits).
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- **xenia simplification.** xenia-rs models FPSCR as a `u32` field but **does not actively maintain** most of the IEEE-754 sticky bits — the FPU paths typically leave FPSCR untouched. So `mffs` will return whatever was last explicitly set (often 0 / boot defaults). Real titles use it mostly to save/restore the rounding-mode field around library calls, which xenia happens to handle correctly.
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- **Not synchronising.** Reorderable with non-FPU instructions.
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## Related Instructions
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- [`mtfsfx`](mtfsfx.md) — write fields of FPSCR from an FPR (the inverse).
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- [`mtfsb0x`](mtfsb0x.md), [`mtfsb1x`](mtfsb1x.md) — set/clear individual FPSCR bits.
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- [`mtfsfix`](mtfsfix.md) — load a 4-bit immediate into one FPSCR field.
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- [`mcrfs`](mcrfs.md) — copy an FPSCR field into a CR field (and clear sticky bits).
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- [`mfspr`](mfspr.md) — for non-FPSCR special registers.
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`mffs` is the simplified mnemonic for the base form (`Rc=0`); `mffs.` is the recording variant.
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## IBM Reference
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- [AIX 7.3 — `mffs` (Move from FPSCR)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-mffs-move-from-fpscr-instruction)
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- PowerISA v2.07B, Book I §4.6 — FPSCR layout and the high-half-undefined rule.
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