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Sylpheed/tools/ppc-manual/memory/stfd.md
sim f3c512f2ab docs(ppc-manual): check every xenia-rs claim against Canary's source 
The hand-written parts of the manual still described how the retired
xenia-rs interpreter behaved: its snapshots, Rust casts and helpers. Each of
those 490 statements is now either restated as what Canary's emitters and
x64 backend actually do (at the pinned canary_experimental commit), or
dropped where it only made sense for xenia-rs.

Checking them turned up claims that were wrong, not just outdated:

- VSCR[SAT] is never modelled in Canary (DID_SATURATE is a stub and mfvscr
  cannot see it); the pages said saturating ops set it stickily.
- Canary does not implement lswi/lswx/stswi/stswx, dcbi, mtfsb0/mtfsb1,
  vmsum*, vmhaddshs, vupkhpx/vupklpx, and most SPRs; pages described them
  as working.
- Traps evaluate TO in Canary; stvebx/stvehx/stvewx store one element, not
  16 bytes; mtmsrd writes only EE; fres/frsqrte/vrsqrtefp precision claims
  and the stfs "rounds under RN / sets FPSCR" claim contradicted the spec.
- Reservations are a 64 KiB block bitmap plus a value compare, not
  per-address tracking.

Claims that neither Canary's source nor a public spec settles are marked
unverified (NI at boot, vmaddcfp128 operand order, estimate bit-exactness).

Generated regions are untouched; re-running the generator changes nothing.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-09-16 21:52:38 +02:00

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# `stfd` — Store Floating-Point Double
> **Category:** [Memory](../categories/memory.md) · **Form:** [D](../forms/D.md) · **Opcode:** `0xd8000000`
<!-- GENERATED: BEGIN -->
## Assembler Mnemonics
| Mnemonic | XML entry | Flags | Description |
| --- | --- | --- | --- |
| `stfd` | `stfd` | — | Store Floating-Point Double |
| `stfdu` | `stfdu` | — | Store Floating-Point Double with Update |
| `stfdux` | `stfdux` | — | Store Floating-Point Double with Update Indexed |
| `stfdx` | `stfdx` | — | Store Floating-Point Double Indexed |
## Syntax
```asm
stfd [FS], [d]([RA0])
stfdu [FS], [d]([RA])
stfdux [FS], [RA], [RB]
stfdx [FS], [RA0], [RB]
```
## Encoding
### `stfd` — form `D`
- **Opcode word:** `0xd8000000`
- **Primary opcode (bits 0–5):** `54`
- **Extended opcode:** —
- **Synchronising:** no
| Bits | Field | Meaning |
| --- | --- | --- |
| 0–5 | `OPCD` | primary opcode |
| 6–10 | `RT` | destination GPR (or RS when storing) |
| 11–15 | `RA` | source GPR (0 ⇒ literal 0 for RA0 forms) |
| 16–31 | `D/SI/UI` | 16-bit signed or unsigned immediate |
### `stfdu` — form `D`
- **Opcode word:** `0xdc000000`
- **Primary opcode (bits 0–5):** `55`
- **Extended opcode:** —
- **Synchronising:** no
| Bits | Field | Meaning |
| --- | --- | --- |
| 0–5 | `OPCD` | primary opcode |
| 6–10 | `RT` | destination GPR (or RS when storing) |
| 11–15 | `RA` | source GPR (0 ⇒ literal 0 for RA0 forms) |
| 16–31 | `D/SI/UI` | 16-bit signed or unsigned immediate |
### `stfdux` — form `X`
- **Opcode word:** `0x7c0005ee`
- **Primary opcode (bits 0–5):** `31`
- **Extended opcode:** `759`
- **Synchronising:** no
| Bits | Field | Meaning |
| --- | --- | --- |
| 0–5 | `OPCD` | primary opcode |
| 6–10 | `RT/FRT/VRT` | destination |
| 11–15 | `RA/FRA/VRA` | source A |
| 16–20 | `RB/FRB/VRB` | source B |
| 21–30 | `XO` | extended opcode (10 bits) |
| 31 | `Rc` | record-form flag |
### `stfdx` — form `X`
- **Opcode word:** `0x7c0005ae`
- **Primary opcode (bits 0–5):** `31`
- **Extended opcode:** `727`
- **Synchronising:** no
| Bits | Field | Meaning |
| --- | --- | --- |
| 0–5 | `OPCD` | primary opcode |
| 6–10 | `RT/FRT/VRT` | destination |
| 11–15 | `RA/FRA/VRA` | source A |
| 16–20 | `RB/FRB/VRB` | source B |
| 21–30 | `XO` | extended opcode (10 bits) |
| 31 | `Rc` | record-form flag |
## Operands
| Field | Role | Description |
| --- | --- | --- |
| `FS` | stfd: read; stfdu: read; stfdux: read; stfdx: read | Source floating-point register. |
| `RA0` | stfd: read; stfdx: read | Source GPR; when the encoded register number is 0 the operand is the literal 64-bit zero, **not** `r0`. |
| `d` | stfd: read; stfdu: read | 16-bit signed displacement (`d`) added to the base address register. |
| `RA` | stfdu: read; stfdu: write; stfdux: read; stfdux: write | Source GPR (`r0`–`r31`). |
| `RB` | stfdux: read; stfdx: read | Source GPR. |
## Register Effects
### `stfd`
- **Reads (always):** `FS`, `RA0`, `d`
- **Reads (conditional):** _none_
- **Writes (always):** _none_
- **Writes (conditional):** _none_
### `stfdu`
- **Reads (always):** `FS`, `RA`, `d`
- **Reads (conditional):** _none_
- **Writes (always):** `RA`
- **Writes (conditional):** _none_
### `stfdux`
- **Reads (always):** `FS`, `RA`, `RB`
- **Reads (conditional):** _none_
- **Writes (always):** `RA`
- **Writes (conditional):** _none_
### `stfdx`
- **Reads (always):** `FS`, `RA0`, `RB`
- **Reads (conditional):** _none_
- **Writes (always):** _none_
- **Writes (conditional):** _none_
## Status-Register Effects
_No condition-register or status-register effects._
## Operation (pseudocode)
```
EA <- (RA|0) + EXTS(d)
MEM(EA, 8) <- (FRS)
```
## C Translation Example
```c
/* 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
**`stfd`**
- Canary XML: [`tools/ppc-instructions.xml` — search for `mnem="stfd"`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/tools/ppc-instructions.xml)
- Canary emitter: [`src/xenia/cpu/ppc/ppc_emit_memory.cc:1014`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/src/xenia/cpu/ppc/ppc_emit_memory.cc#L1014)
- Sylpheed opcode: [`crates/sylpheed-ppc/src/opcode.rs:237`](../../../crates/sylpheed-ppc/src/opcode.rs#L237)
- Sylpheed decoder: [`crates/sylpheed-ppc/src/decoder.rs:492`](../../../crates/sylpheed-ppc/src/decoder.rs#L492)
<details><summary>Canary emitter (frozen snapshot @ <code>f21ebd49e9</code>)</summary>
```cpp
int InstrEmit_stfd(PPCHIRBuilder& f, const InstrData& i) {
// if RA = 0 then
// b <- 0
// else
// b <- (RA)
// EA <- b + EXTS(D)
// MEM(EA, 8) <- (FRS)
Value* ea = CalculateEA_0_i(f, i.D.RA, XEEXTS16(i.D.DS));
f.Store(ea, f.ByteSwap(f.Cast(f.LoadFPR(i.D.RT), INT64_TYPE)));
return 0;
}
```
</details>
**`stfdu`**
- Canary XML: [`tools/ppc-instructions.xml` — search for `mnem="stfdu"`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/tools/ppc-instructions.xml)
- Canary emitter: [`src/xenia/cpu/ppc/ppc_emit_memory.cc:1026`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/src/xenia/cpu/ppc/ppc_emit_memory.cc#L1026)
- Sylpheed opcode: [`crates/sylpheed-ppc/src/opcode.rs:238`](../../../crates/sylpheed-ppc/src/opcode.rs#L238)
- Sylpheed decoder: [`crates/sylpheed-ppc/src/decoder.rs:493`](../../../crates/sylpheed-ppc/src/decoder.rs#L493)
<details><summary>Canary emitter (frozen snapshot @ <code>f21ebd49e9</code>)</summary>
```cpp
int InstrEmit_stfdu(PPCHIRBuilder& f, const InstrData& i) {
// EA <- (RA) + EXTS(D)
// MEM(EA, 8) <- (FRS)
// RA <- EA
Value* ea = CalculateEA_i(f, i.D.RA, XEEXTS16(i.D.DS));
f.Store(ea, f.ByteSwap(f.Cast(f.LoadFPR(i.D.RT), INT64_TYPE)));
StoreEA(f, i.D.RA, ea);
return 0;
}
```
</details>
**`stfdux`**
- Canary XML: [`tools/ppc-instructions.xml` — search for `mnem="stfdux"`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/tools/ppc-instructions.xml)
- Canary emitter: [`src/xenia/cpu/ppc/ppc_emit_memory.cc:1036`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/src/xenia/cpu/ppc/ppc_emit_memory.cc#L1036)
- Sylpheed opcode: [`crates/sylpheed-ppc/src/opcode.rs:239`](../../../crates/sylpheed-ppc/src/opcode.rs#L239)
- Sylpheed decoder: [`crates/sylpheed-ppc/src/decoder.rs:952`](../../../crates/sylpheed-ppc/src/decoder.rs#L952)
<details><summary>Canary emitter (frozen snapshot @ <code>f21ebd49e9</code>)</summary>
```cpp
int InstrEmit_stfdux(PPCHIRBuilder& f, const InstrData& i) {
// EA <- (RA) + (RB)
// MEM(EA, 8) <- (FRS)
// RA <- EA
Value* ea = CalculateEA(f, i.X.RA, i.X.RB);
f.Store(ea, f.ByteSwap(f.Cast(f.LoadFPR(i.X.RT), INT64_TYPE)));
StoreEA(f, i.X.RA, ea);
return 0;
}
```
</details>
**`stfdx`**
- Canary XML: [`tools/ppc-instructions.xml` — search for `mnem="stfdx"`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/tools/ppc-instructions.xml)
- Canary emitter: [`src/xenia/cpu/ppc/ppc_emit_memory.cc:1046`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/src/xenia/cpu/ppc/ppc_emit_memory.cc#L1046)
- Sylpheed opcode: [`crates/sylpheed-ppc/src/opcode.rs:240`](../../../crates/sylpheed-ppc/src/opcode.rs#L240)
- Sylpheed decoder: [`crates/sylpheed-ppc/src/decoder.rs:951`](../../../crates/sylpheed-ppc/src/decoder.rs#L951)
<details><summary>Canary emitter (frozen snapshot @ <code>f21ebd49e9</code>)</summary>
```cpp
int InstrEmit_stfdx(PPCHIRBuilder& f, const InstrData& i) {
// if RA = 0 then
// b <- 0
// else
// b <- (RA)
// EA <- b + (RB)
// MEM(EA, 8) <- (FRS)
Value* ea = CalculateEA_0(f, i.X.RA, i.X.RB);
f.Store(ea, f.ByteSwap(f.Cast(f.LoadFPR(i.X.RT), INT64_TYPE)));
return 0;
}
```
</details>
<!-- GENERATED: END -->
## Special Cases & Edge Conditions
- **Bit-exact double store.** Writes the 64-bit IEEE binary64 contents of `FRS` directly to memory; no rounding, no format conversion. Canary reinterprets the FPR as a 64-bit integer (`Cast`) and stores it byte-swapped, which preserves the exact bit pattern (including signalling NaNs).
- **No FPSCR side effects.** Like [`lfd`](lfd.md), `stfd` cannot raise IEEE exceptions: there is no rounding step. Contrast [`stfs`](stfs.md), where double→single rounding **can** raise inexact / overflow / underflow.
- **`RA0` (non-update forms).** `RA = 0` in `stfd` and `stfdx` selects literal zero. Update forms `stfdu` / `stfdux` invoke `RA = 0` as an invalid form.
- **Update-form post-write.** `stfdu` / `stfdux` write the computed `EA` back to `RA` after the store. No `FRS` / `RA` collision possible — `RS` is an FPR, `RA` is a GPR.
- **Big-endian write.** Byte at `EA` is the FPR's most-significant byte (sign + part of exponent), byte at `EA+7` is the least-significant mantissa byte. Canary byte-swaps before the host store.
- **Alignment.** Xenon tolerates unaligned 8-byte FP stores. PowerISA permits implementations to raise alignment exceptions on cache-inhibited storage.
- **MSR[FP] required.** Disabled FP unit raises Floating-Point Unavailable.
## Related Instructions
- [`lfd`](lfd.md), [`lfdu`](lfd.md), [`lfdx`](lfd.md), [`lfdux`](lfd.md) — corresponding loads.
- [`stfs`](stfs.md) — single-precision store with format conversion (can raise FPSCR).
- [`stfiwx`](stfiwx.md) — store low 32 bits of FPR as integer word.
- [`std`](std.md) — integer doubleword store (same width, GPR source).
## IBM Reference
- [AIX 7.3 — `stfd` (Store Floating-Point Double)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-stfd-store-floating-point-double-instruction)
- [AIX 7.3 — `stfdu` / `stfdx` / `stfdux`](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-stfdu-store-floating-point-double-update-instruction)
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