7f8a81b8f8
The generator had not been able to run correctly since the manual moved into
`tools/ppc-manual/`: it computed the repository root as `HERE.parent.parent`,
which now names `tools/`, so the XML, Canary's emitters and xenia-rs all stopped
resolving — silently, because both scrapers skipped what they could not find.
Every page's references had been pointing at paths that exist nowhere.
What each source contributed, measured on the 350 pages before this change:
Operation (pseudocode) 251 pages: fixed boilerplate "derives from the xenia-rs
interpreter"; 99 carry real hand-written seeds
C translation 337 pages: the same kind of boilerplate
xenia-rs snapshot 336 pages: the interpreter arm, pasted in — the only
per-instruction semantics on unseeded pages
links xenia-rs opcode/decoder/interpreter + Canary emitter
Now:
* semantics come from **Xenia Canary**, the reference emulator, read through
`git show` at a pinned upstream commit (`origin/canary_experimental`,
f21ebd49e9). Not our checkout: it carries instrumentation and lacked
upstream's `mcrf` fix, so it would have published probes and a wrong `mcrf`.
Each page embeds the emitter (`InstrEmit_<mnem>`), and for the 128 pure
one-line delegations also the helper that holds the semantics.
* decode references point at `crates/sylpheed-ppc` — the decoder that
produces `sylpheed.db` — as in-repo relative links.
* the boilerplate now says what is true, and the C translation guide maps
Canary's actual HIR calls, checked against `ppc_hir_builder.h` (including
that `UpdateCR(n, v)` truncates to 32 bits).
* `rust_scraper.py` -> `decoder_scraper.py` (interpreter half dropped);
missing sources are now errors, not empty results.
Verified:
consistency checks 455 XML entries, 350 families, 598 index keys
hand-written tails 386/386 byte-identical after regeneration
xenia-rs in generated 0
pages with a snapshot 349/350 (was 336) — `dcbi` has no Canary emitter at all
in-repo decoder links 910/910 resolve to a line holding the identifier
emitter boundaries brace counter == column-0 `}` rule on 521/521;
preprocessor model unit-tested (#if 0/#else/#elif)
idempotency re-run: 0 pages updated, 0 working-tree changes
Hand-written notes (outside the generated regions) are not rewritten here:
* 110 links into `../../xenia-rs/...` were dead; they now point at the file in
the archived repository (git.mc02.dev/fabi/xenia-rs @ 8401d4d). Line anchors
were dropped because the notes predate that commit — 0 of 441 old line
ranges match it — and a precise-looking wrong anchor is worse than none. The
link text, which carries the author's line numbers, is unchanged.
* 140 prose claims about xenia-rs's behaviour remain. 23 are verified to hold
for Canary too (the 32-bit CR0 truncation, OE left unimplemented); the other
114 need checking one by one, and some invert — e.g. `divdx` notes a correct
64-bit CR0 update in xenia-rs where Canary's `UpdateCR` truncates. Left for
a deliberate pass rather than a blind substitution.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
5.4 KiB
5.4 KiB
vmsummbm — Vector Multiply-Sum Mixed-Sign Byte Modulo
Category: VMX (Altivec) · Form: VA · Opcode:
0x10000025
Assembler Mnemonics
| Mnemonic | XML entry | Flags | Description |
|---|---|---|---|
vmsummbm |
vmsummbm |
— | Vector Multiply-Sum Mixed-Sign Byte Modulo |
Syntax
vmsummbm [VD], [VA], [VB], [VC]
Encoding
vmsummbm — form VA
- Opcode word:
0x10000025 - Primary opcode (bits 0–5):
4 - Extended opcode:
37 - Synchronising: no
| Bits | Field | Meaning |
|---|---|---|
| 0–5 | OPCD |
primary opcode (4) |
| 6–10 | VRT |
destination vector register |
| 11–15 | VRA |
source A |
| 16–20 | VRB |
source B |
| 21–25 | VRC |
source C / shift |
| 26–31 | XO |
extended opcode (6 bits) |
Operands
| Field | Role | Description |
|---|---|---|
VA |
vmsummbm: read | Source A vector register. |
VB |
vmsummbm: read | Source B vector register. |
VC |
vmsummbm: read | Source C vector register / 3-bit selector. |
VD |
vmsummbm: write | Destination vector register. |
Register Effects
vmsummbm
- Reads (always):
VA,VB,VC - Reads (conditional): none
- Writes (always):
VD - Writes (conditional): none
Status-Register Effects
No condition-register or status-register effects.
Operation (pseudocode)
; No hand-written pseudocode for this instruction yet.
; The authoritative semantics are the Canary emitter snapshot under
; Implementation References; about half of Canary's emitters open
; with the PPC-style definition as a comment (`RD <- (RA) + (RB)`).
; Every side effect is also enumerated in the Register Effects and
; Status-Register Effects tables above.
C Translation Example
/* No hand-written C yet. Translate the Canary emitter snapshot */
/* under Implementation References; its HIR maps directly: */
/* f.LoadGPR(n) / f.StoreGPR(n, v) -> r[n] / r[n] = v */
/* f.LoadFPR / StoreFPR, f.LoadVR / StoreVR -> f[n], v[n] */
/* f.Load(ea, T), f.Store(ea, v) -> raw read / write; emitters */
/* wrap them in f.ByteSwap for the big-endian guest value */
/* f.UpdateCR(n, v) -> CR field n from v's LOW 32 BITS vs 0 */
/* f.LoadCA / f.StoreCA -> xer.CA; f.StoreSAT -> vscr.SAT */
/* i.XO.RA, i.D.DS, ... -> the bit-fields listed under Operands */
/* The Register Effects and Status-Register Effects tables above */
/* enumerate every side effect a faithful translation must emit. */
Implementation References
vmsummbm
- Canary XML:
tools/ppc-instructions.xml— search formnem="vmsummbm" - Canary emitter:
src/xenia/cpu/ppc/ppc_emit_altivec.cc:1024 - Sylpheed opcode:
crates/sylpheed-ppc/src/opcode.rs:379 - Sylpheed decoder:
crates/sylpheed-ppc/src/decoder.rs:695
Canary emitter (frozen snapshot @ f21ebd49e9)
int InstrEmit_vmsummbm(PPCHIRBuilder& f, const InstrData& i) {
XEINSTRNOTIMPLEMENTED();
return 1;
}
Special Cases & Edge Conditions
- Mixed signed×unsigned multiply-sum, modulo. The "m" / "b" / "m" of
vmsummbmdecode as:m=mixed (signedVA× unsignedVB),b=byte lanes,m=modulo accumulator. Per word lane:Four signed-byte × unsigned-byte products are summed with a signed-word accumulator fromVD[i] = (VC[i] + Σ_{j=0..3} int8(VA[4*i + j]) * uint8(VB[4*i + j])) mod 2^32VC, into a single signed word. - Mixed signedness is unique to this instruction — it's the canonical "signed pixel weight × unsigned pixel value" combo for filter convolution.
- No
VSCR[SAT]change. Modulo wrap; the saturating sibling for byte lanes does not exist (Altivec only provides a saturatingvmsumfor half-word widths). - Big-endian byte lanes. Lane 0 is the most-significant byte; the four contributing bytes for output word
iare bytes4*i .. 4*i+3. - No XER, no exceptions.
- Aliasing legal.
- No VMX128 sibling.
- Common usage. Per-tile signed-weight pixel sums; H.264-style 4-tap signed filter on byte data.
Related Instructions
vmsumubm— same shape, both sources unsigned (no signed weights).vmsumshm/vmsumshs— half-word × half-word multiply-sum (modulo / saturate).vmsumuhm/vmsumuhs— unsigned half-word multiply-sum.vmladduhm— per-lane multiply-add at half width (no horizontal reduction).vsumsws,vsum4sbs— pure horizontal sums.