Sylpheed/tools/ppc-manual/alu/cmpl.md

# `cmpl` — Compare Logical

> **Category:** [Integer ALU](../categories/alu.md) · **Form:** [X](../forms/X.md) · **Opcode:** `0x7c000040`

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## Assembler Mnemonics

| Mnemonic | XML entry | Flags | Description |
| --- | --- | --- | --- |
| `cmpl` | `cmpl` | — | Compare Logical |

## Syntax

```asm
cmpl [CRFD], [L], [RA], [RB]
```

## Encoding

### `cmpl` — form `X`

- **Opcode word:** `0x7c000040`
- **Primary opcode (bits 0–5):** `31`
- **Extended opcode:** `32`
- **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 |
| --- | --- | --- |
| `L` | cmpl: read | Operand-length bit for compare instructions (`0 ⇒ 32-bit`, `1 ⇒ 64-bit`). |
| `RA` | cmpl: read | Source GPR (`r0`–`r31`). |
| `RB` | cmpl: read | Source GPR. |
| `CRFD` | cmpl: write | CR destination field (`crf`, 0–7). |

## Register Effects

### `cmpl`

- **Reads (always):** `L`, `RA`, `RB`
- **Reads (conditional):** _none_
- **Writes (always):** `CRFD`
- **Writes (conditional):** _none_

## Status-Register Effects

_No condition-register or status-register effects._

## Operation (pseudocode)

```
if L = 0 then a,b <- (RA)[32:63], (RB)[32:63]
else             a,b <- (RA), (RB)
CR[BF] <- unsigned_compare(a, b) || XER[SO]
```

## 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

**`cmpl`**
- Canary XML: [`tools/ppc-instructions.xml` — search for `mnem="cmpl"`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/tools/ppc-instructions.xml)
- Canary emitter: [`src/xenia/cpu/ppc/ppc_emit_alu.cc:579`](https://github.com/xenia-canary/xenia-canary/blob/f21ebd49e979e44f081f474df78c3fbfee9cb3f2/src/xenia/cpu/ppc/ppc_emit_alu.cc#L579)
- Sylpheed opcode: [`crates/sylpheed-ppc/src/opcode.rs:29`](../../../crates/sylpheed-ppc/src/opcode.rs#L29)
- Sylpheed decoder: [`crates/sylpheed-ppc/src/decoder.rs:876`](../../../crates/sylpheed-ppc/src/decoder.rs#L876)
<details><summary>Canary emitter (frozen snapshot @ <code>f21ebd49e9</code>)</summary>

```cpp
int InstrEmit_cmpl(PPCHIRBuilder& f, const InstrData& i) {
  // if L = 0 then
  //   a <- i32.0 || (RA)[32:63]
  //   b <- i32.0 || (RB)[32:63]
  // else
  //   a <- (RA)
  //   b <- (RB)
  // if a <u b then
  //   c <- 0b100
  // else if a >u b then
  //   c <- 0b010
  // else
  //   c <- 0b001
  // CR[4×BF+32:4×BF+35] <- c || XER[SO]
  uint32_t BF = i.X.RT >> 2;
  uint32_t L = i.X.RT & 1;
  Value* lhs;
  Value* rhs;
  if (L) {
    lhs = f.LoadGPR(i.X.RA);
    rhs = f.LoadGPR(i.X.RB);
  } else {
    lhs = f.Truncate(f.LoadGPR(i.X.RA), INT32_TYPE);
    rhs = f.Truncate(f.LoadGPR(i.X.RB), INT32_TYPE);
  }
  f.UpdateCR(BF, lhs, rhs, false);
  return 0;
}
```
</details>

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## Special Cases & Edge Conditions

- **Unsigned compare.** Treats both operands as unsigned magnitudes. The simplified mnemonics are `cmplw` (`L=0`) and `cmpld` (`L=1`).
- **`L = 0`: 32-bit operands.** Canary truncates both registers to 32 bits before the unsigned compare, so the high 32 bits of `RA`/`RB` are ignored — this matches spec `(RA)[32:63]` semantics. Most Xbox 360 code uses this mode.
- **`L = 1`: full 64-bit unsigned compare.** Used in 64-bit pointer arithmetic; rare in game code but appears in kernel-side helpers.
- **SO is copied from `XER[SO]`.** `cmpl` does not clear or set sticky overflow; it just exposes the current `SO` in the destination CR field's `SO` slot.
- **`BF` is a CR field 0–7.** Same convention as [`cmp`](cmp.md). Two consecutive `cmpl` instructions with the same `BF` simply overwrite the previous result.
- **Common signed/unsigned bug.** Misusing `cmp` instead of `cmpl` (or vice versa) for pointer comparisons is the canonical bug in PPC porting; pointers are always unsigned in C semantics. Always cross-check the comparison polarity in disassembly.
- **No `Rc`/`OE`** and no GPR write — purely a CR-field producer.

## Related Instructions

- [`cmp`](cmp.md) — signed register compare.
- [`cmpli`](cmpli.md) — unsigned compare against a 16-bit immediate.
- [`cmpi`](cmpi.md) — signed immediate compare.
- `cmplw`, `cmpld` (simplified) — preferred forms in disassembly.
- [`mcrxr`](../control/mcrxr.md) — clear sticky overflow.

## IBM Reference

- [AIX 7.3 — `cmpl` (Compare Logical)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-cmpl-compare-logical-instruction)
- [AIX 7.3 — `cmplw` / `cmpld` (simplified mnemonics)](https://www.ibm.com/docs/en/aix/7.3.0?topic=mnemonics-cmplw-compare-logical-word)