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dedcf37867ce3a51f00e90aef2ac2948e3eab76b
Sylpheed/tools/ppc-manual/control/crand.md
sim dedcf37867 docs(ppc-manual): quote Canary and our own decoder, not the retired xenia-rs 
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>
2026-09-16 20:34:34 +02:00

6.1 KiB
Raw Blame History

crand — Condition Register AND

Category: Control / CR / SPR · Form: XL · Opcode: 0x4c000202

Assembler Mnemonics

Mnemonic XML entry Flags Description
crand crand — Condition Register AND

Syntax

crand [CRBD], [CRBA], [CRBB]

Encoding

crand — form XL

  • Opcode word: 0x4c000202
  • Primary opcode (bits 0–5): 19
  • Extended opcode: 257
  • Synchronising: no
Bits Field Meaning
0–5 OPCD primary opcode (19)
6–10 BT/BO target / branch options
11–15 BA/BI source A / CR bit to test
16–20 BB source B
21–30 XO extended opcode (10 bits)
31 LK link flag

Operands

Field Role Description
CRBA crand: read CR source bit A (0–31).
CRBB crand: read CR source bit B (0–31).
CRBD crand: write CR destination bit (0–31).

Register Effects

crand

  • Reads (always): CRBA, CRBB
  • Reads (conditional): none
  • Writes (always): CRBD
  • 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

crand

Canary emitter (frozen snapshot @ f21ebd49e9) 
int InstrEmit_crand(PPCHIRBuilder& f, const InstrData& i) {
  // CR[bt] <- CR[ba] & CR[bb]   bt=bo, ba=bi, bb=bb
  Value* ba = f.LoadCRField(i.XL.BI >> 2, i.XL.BI & 3);
  Value* bb = f.LoadCRField(i.XL.BB >> 2, i.XL.BB & 3);
  Value* bt = f.And(ba, bb);
  f.StoreCRField(i.XL.BO >> 2, i.XL.BO & 3, bt);
  return 0;
}

Special Cases & Edge Conditions

  • Bit-level granularity. All eight CR-logical instructions operate on single CR bits, not whole 4-bit fields. CRBD, CRBA, CRBB are 5-bit absolute indices into the 32-bit CR register: BI = 4·field + bit-within-field, where bit 0 = LT, 1 = GT, 2 = EQ, 3 = SO.
  • Operation. CR[CRBD] ← CR[CRBA] AND CR[CRBB]. All other CR bits are preserved.
  • Same-source / same-destination quirks. Identical sources and destinations are legal: crand 6, 6, 6 is a NOP-style "force CR bit 6 to itself"; crand bt, bt, bt reads-then-writes the same bit (no observable change). Compilers exploit crxor BT,BT,BT ("clear bit") and creqv BT,BT,BT ("set bit") for similar tricks — see those pages.
  • Combining branch conditions. The classic use: synthesise complex branch conditions from multiple compare results. Example: cmpw cr0, r3, r4; cmpw cr1, r5, r6; crand 4*cr0+2, 4*cr0+2, 4*cr1+2; beq cr0, label branches if r3==r4 AND r5==r6 using a single conditional branch.
  • No Rc / OE. XL-form CR-logical ops never set CR0 or XER; they only update the named CR bit.
  • Not synchronising. Pure data-flow on CR; freely reorderable.
  • xenia status. xenia-rs decodes crand (decoder slot 540) but the interpreter snapshot is not embedded on this page — implementation lives in crates/xenia-cpu/src/interpreter.rs. xenia-canary's InstrEmit_crand emits the equivalent host AND of the two CR bits.

Related Instructions

  • crandc — AND with complement: CR[BT] ← CR[BA] AND ¬CR[BB].
  • cror, crorc — OR / OR-with-complement.
  • crnand, crnor — negated AND / OR.
  • crxor, creqv — XOR and equivalence (XNOR).
  • mcrf — copy a whole 4-bit CR field.
  • bcx consumers — the typical reason to compute composite CR bits.

Simplified Mnemonics

  • crmove BT, BA ≡ cror BT, BA, BA (use cror, not crand).
  • crset BT ≡ creqv BT, BT, BT (set to 1).
  • crclr BT ≡ crxor BT, BT, BT (clear to 0).

crand itself has no dedicated simplified mnemonic.

IBM Reference

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