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>
137 lines
6.0 KiB
Markdown
137 lines
6.0 KiB
Markdown
# `divdx` — Divide Doubleword
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> **Category:** [Integer ALU](../categories/alu.md) · **Form:** [XO](../forms/XO.md) · **Opcode:** `0x7c0003d2`
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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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| `divd` | `divdx` | — | Divide Doubleword |
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| `divdo` | `divdx` | OE=1 | Divide Doubleword |
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| `divd.` | `divdx` | Rc=1 | Divide Doubleword |
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| `divdo.` | `divdx` | OE=1, Rc=1 | Divide Doubleword |
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## Syntax
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```asm
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divd[OE][Rc] [RD], [RA], [RB]
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```
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## Encoding
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### `divdx` — form `XO`
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- **Opcode word:** `0x7c0003d2`
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- **Primary opcode (bits 0–5):** `31`
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- **Extended opcode:** `489`
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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 (31) |
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| 6–10 | `RT` | destination GPR |
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| 11–15 | `RA` | source A |
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| 16–20 | `RB` | source B |
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| 21 | `OE` | overflow-enable flag |
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| 22–30 | `XO` | extended opcode (9 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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| `RA` | divdx: read | Source GPR (`r0`–`r31`). |
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| `RB` | divdx: read | Source GPR. |
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| `RD` | divdx: write | Destination GPR. |
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| `OE` | divdx: write (conditional) | Overflow-enable bit. When 1, the instruction updates `XER[OV]` and stickies `XER[SO]` on signed overflow. |
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| `CR` | divdx: 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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### `divdx`
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- **Reads (always):** `RA`, `RB`
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- **Reads (conditional):** _none_
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- **Writes (always):** `RD`
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- **Writes (conditional):** `OE`, `CR`
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## Status-Register Effects
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- `divdx`: **CR0** ← signed-compare(result, 0) with `SO ← XER[SO]`, when `Rc=1`.; **XER[OV]** ← signed-overflow(result); **XER[SO]** stickies, when `OE=1`.
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## Operation (pseudocode)
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```
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RT <- (RA) /s (RB) ; undefined if RB=0 or (RA=-2^63 and RB=-1)
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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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**`divdx`**
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- xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="divdx"`](../../xenia-canary/tools/ppc-instructions.xml)
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- xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_alu.cc:192`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_alu.cc#L192)
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- xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:21`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L21)
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- xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:878`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L878)
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- xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:463-479`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L463-L479)
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<details><summary>xenia-rs interpreter body (frozen snapshot)</summary>
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```rust
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PpcOpcode::divdx => {
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let ra = ctx.gpr[instr.ra()] as i64;
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let rb = ctx.gpr[instr.rb()] as i64;
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let ov = overflow::divd_ov_signed(ra, rb);
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if ov {
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ctx.gpr[instr.rd()] = 0;
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} else {
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ctx.gpr[instr.rd()] = (ra / rb) as u64;
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}
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if instr.oe() {
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overflow::apply(ctx, ov);
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}
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if instr.rc_bit() {
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ctx.update_cr_signed(0, ctx.gpr[instr.rd()] as i64);
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}
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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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- **Two undefined-behaviour cases.** Division by zero (`RB == 0`) and signed-min divided by negative-one (`RA == INT64_MIN && RB == -1`, which would mathematically produce `2^63`, unrepresentable in `i64`). PowerISA leaves `RT` *boundedly undefined* in both cases; **xenia-rs returns 0** ([`interpreter.rs:293`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L293)). Matching this behaviour bit-for-bit is a defacto-spec on Xenon.
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- **No exception raised.** Xenon does not trap on either undefined case; the consuming code is expected to have validated `RB` first, e.g. with `cmpdi`/`bne`. If you need a trap, follow the divide with [`tw`](../control/tw.md)/`twi` (these live outside the ALU page set).
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- **`OE=1` should set `XER[OV]`** for both undefined cases plus any operand triggering overflow; xenia-rs does not implement the `OE` branch.
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- **`Rc=1` CR0 update is correctly 64-bit here.** Unlike most ALU pages, [`interpreter.rs:298`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L298) uses `as i64` (no `as i32` truncation) — divide is one of the few xenia-rs instructions that already matches Xenon spec for the CR0 width.
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- **Latency.** Integer divide is the slowest ALU instruction on Xenon — 70+ cycles, non-pipelined. Hot inner loops avoid it via reciprocal-multiply or shift; expect to see `mulhwu`-based reciprocals in optimised disassembly.
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- **Rounds toward zero.** The signed quotient truncates toward zero, matching C99/C++11 `/` semantics. Use [`mulldx`](mulldx.md) and a subtract to recover the remainder; there is no `divmod` instruction.
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## Related Instructions
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- [`divdux`](divdux.md) — unsigned 64-bit divide.
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- [`divwx`](divwx.md), [`divwux`](divwux.md) — 32-bit signed/unsigned variants.
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- [`mulldx`](mulldx.md), [`mulhdx`](mulhdx.md) — multiply pair used to compute the remainder.
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- [`cmpi`](cmpi.md), [`cmp`](cmp.md) — guard the divisor before invoking divide.
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## IBM Reference
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- [AIX 7.3 — `divd` (Divide Doubleword)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-divd-divide-double-word-instruction)
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- PowerISA v2.07B, Book I, §3.3.9 — defines the boundedly-undefined behaviour for `RB=0` and `INT_MIN/−1`.
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