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>
147 lines
6.3 KiB
Markdown
147 lines
6.3 KiB
Markdown
# `vmhraddshs` — Vector Multiply-High Round and Add Signed Signed Half Word Saturate
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> **Category:** [VMX (Altivec)](../categories/vmx.md) · **Form:** [VA](../forms/VA.md) · **Opcode:** `0x10000021`
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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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| `vmhraddshs` | `vmhraddshs` | — | Vector Multiply-High Round and Add Signed Signed Half Word Saturate |
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## Syntax
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```asm
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vmhraddshs [VD], [VA], [VB], [VC]
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```
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## Encoding
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### `vmhraddshs` — form `VA`
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- **Opcode word:** `0x10000021`
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- **Primary opcode (bits 0–5):** `4`
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- **Extended opcode:** `33`
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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 (4) |
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| 6–10 | `VRT` | destination vector register |
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| 11–15 | `VRA` | source A |
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| 16–20 | `VRB` | source B |
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| 21–25 | `VRC` | source C / shift |
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| 26–31 | `XO` | extended opcode (6 bits) |
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## Operands
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| Field | Role | Description |
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| --- | --- | --- |
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| `VA` | vmhraddshs: read | Source A vector register. |
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| `VB` | vmhraddshs: read | Source B vector register. |
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| `VC` | vmhraddshs: read | Source C vector register / 3-bit selector. |
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| `VD` | vmhraddshs: write | Destination vector register. |
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| `VSCR` | vmhraddshs: write | Vector Status and Control Register (NJ/SAT bits). |
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## Register Effects
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### `vmhraddshs`
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- **Reads (always):** `VA`, `VB`, `VC`
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- **Reads (conditional):** _none_
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- **Writes (always):** `VD`, `VSCR`
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- **Writes (conditional):** _none_
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## Status-Register Effects
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- `vmhraddshs`: **VSCR[SAT]** may be stickied on saturating vector operations.
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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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**`vmhraddshs`**
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- xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="vmhraddshs"`](../../xenia-canary/tools/ppc-instructions.xml)
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- xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_altivec.cc:888`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_altivec.cc#L888)
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- xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:102`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L102)
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- xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:577`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L577)
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- xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:3534-3548`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L3534-L3548)
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<details><summary>xenia-rs interpreter body (frozen snapshot)</summary>
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```rust
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PpcOpcode::vmhraddshs => {
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// Rounded multiply-add: (vA[i]*vB[i] + 0x4000) >> 15 + vC[i], saturating.
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let a = crate::vmx::as_i16x8(ctx.vr[instr.ra()]);
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let b = crate::vmx::as_i16x8(ctx.vr[instr.rb()]);
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let c = crate::vmx::as_i16x8(ctx.vr[instr.rc()]);
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let mut r = [0i16; 8]; let mut sat = false;
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for i in 0..8 {
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let prod = (a[i] as i32 * b[i] as i32 + 0x4000) >> 15;
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let (v, s) = crate::vmx::sat_i32_to_i16(prod + c[i] as i32);
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r[i] = v; sat |= s;
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}
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if sat { ctx.set_vscr_sat(true); }
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ctx.vr[instr.rd()] = crate::vmx::from_i16x8(r);
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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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- **Rounded Q15 fixed-point multiply-add, saturating.** Eight half-word lanes; per lane:
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```
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prod = (int16(VA[i]) * int16(VB[i]) + 0x4000) >> 15 ; round half-up
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VD[i] = clamp(prod + int16(VC[i]), -32768, +32767)
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```
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Identical to [`vmhaddshs`](vmhaddshs.md) except for the `+0x4000` rounding bias before the shift.
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- **Half-up rounding to even-magnitude.** The `+0x4000` bias rounds the discarded low 15 bits *toward* the nearest representable value, with ties broken away from zero. For most DSP work this is the desired behaviour and gives lower mean error than the truncating variant.
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- **`VSCR[SAT]` is sticky-set** if the final sum overflows `int16`. The rounding bias can itself push a lane that was at `+32767` past the cap — important for tight Q15 audio where the truncating form might not have saturated.
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- **Same `0x8000 * 0x8000 >> 15` gotcha** as `vmhaddshs`: the product is `+32768.5` rounded to `+32769`, which still saturates.
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- **Big-endian half lanes.** Lane 0 is the most-significant half.
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- **No XER changes, no exceptions.**
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- **No VMX128 sibling.**
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- **Common usage.** High-quality Q15 audio filter taps where round-toward-nearest is preferred over truncate-toward-zero.
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## Related Instructions
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- [`vmhaddshs`](vmhaddshs.md) — same op without the rounding bias.
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- [`vmladduhm`](vmladduhm.md) — same shape, modulo (no shift, no saturate), unsigned.
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- [`vmsumshs`](vmsumshs.md), [`vmsumshm`](vmsumshm.md) — multiply-sum across pairs of lanes.
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- [`vaddshs`](vaddshs.md), [`vmaxsh`](vmaxsh.md) — saturating add and max at same lane width.
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## IBM Reference
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- [AIX 7.3 — `vmhraddshs` (Vector Multiply-High Round and Add Signed Half Word Saturate)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-vmhraddshs-vector-multiply-high-round-add-signed-half-word-saturate-instruction)
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- [IBM AltiVec Technology Programmer's Interface Manual, Chapter 6 — Multiply-Add Family](https://www.nxp.com/docs/en/reference-manual/ALTIVECPIM.pdf)
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