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

# `addic.` — Add Immediate Carrying and Record

> **Category:** [Integer ALU](../categories/alu.md) · **Form:** [D](../forms/D.md) · **Opcode:** `0x34000000`

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## Assembler Mnemonics

| Mnemonic | XML entry | Flags | Description |
| --- | --- | --- | --- |
| `addic.` | `addic.` | — | Add Immediate Carrying and Record |

## Syntax

```asm
addic. [RD], [RA], [SIMM]
```

## Encoding

### `addic.` — form `D`

- **Opcode word:** `0x34000000`
- **Primary opcode (bits 0–5):** `13`
- **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 |

## Operands

| Field | Role | Description |
| --- | --- | --- |
| `RA` | addic.: read | Source GPR (`r0`–`r31`). |
| `SIMM` | addic.: read | 16-bit signed immediate. Sign-extended to 64 bits before use. |
| `RD` | addic.: write | Destination GPR. |
| `CA` | addic.: write | XER[CA] carry bit. Read by add-with-carry/subtract-with-borrow instructions, written by carrying instructions. |
| `CR` | addic.: write | Condition-register update. When `Rc=1`, CR field 0 (or CR6 for vector compares, CR1 for FPU) is updated from the result. |

## Register Effects

### `addic.`

- **Reads (always):** `RA`, `SIMM`
- **Reads (conditional):** _none_
- **Writes (always):** `RD`, `CA`, `CR`
- **Writes (conditional):** _none_

## Status-Register Effects

- `addic.`: **CR0** ← signed-compare(result, 0) with `SO ← XER[SO]` (always).; **XER[CA]** ← carry-out of the add / borrow-in of the subtract (always).

## Operation (pseudocode)

```
; Pseudocode derives directly from the xenia-rs interpreter
; arm (see Implementation References). Operation semantics:
;   - Read source operands from the fields listed under Operands.
;   - Apply the arithmetic / logical / memory action described
;     in the Description field above.
;   - Write results to the destination register(s); update any
;     status bits enumerated under Status-Register Effects.
; Consult the IBM AIX reference link under IBM Reference for
; canonical PPC-style pseudocode where xenia's expression is
; terse.
```

## C Translation Example

```c
/* C translation: the xenia-rs interpreter arm below in           */
/* Implementation References is the authoritative semantic        */
/* snapshot. Translate it line-by-line:                            */
/*   - ctx.gpr[N]  -> r[N]       (or f[]/v[] for FPRs/VRs)        */
/*   - mem.read_u*/write_u* -> mem_read_u*_be / mem_write_u*_be   */
/*   - ctx.update_cr_signed(fld, v) -> update_cr_signed(fld, v)   */
/*   - ctx.xer_ca / xer_ov / xer_so -> xer.CA / xer.OV / xer.SO   */
/* The Register Effects and Status-Register Effects tables above  */
/* enumerate every side effect a faithful translation must emit.  */
```

## Implementation References

**`addic.`**
- xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="addic."`](../../xenia-canary/tools/ppc-instructions.xml)
- xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_alu.cc:127`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_alu.cc#L127)
- xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:8`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L8)
- xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:337`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L337)
- xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:145-154`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L145-L154)
<details><summary>xenia-rs interpreter body (frozen snapshot)</summary>

```rust
        PpcOpcode::addicx => {
            // PPCBUG-003: same fix as addic plus CR0 i32 view.
            let ra32 = ctx.gpr[instr.ra()] as u32;
            let imm32 = instr.simm16() as i32 as u32;
            let result32 = ra32.wrapping_add(imm32);
            ctx.xer_ca = if result32 < ra32 { 1 } else { 0 };
            ctx.gpr[instr.rd()] = result32 as u64;
            ctx.update_cr_signed(0, result32 as i32 as i64);
            ctx.pc += 4;
        }
```
</details>

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## Special Cases & Edge Conditions

- **`Rc` bit is implicit, not encoded.** `addic.` has its *own* primary opcode (13) distinct from `addic`'s (12); there is no `Rc` field to set. The two forms are sibling D-form instructions, not flag variants of one encoding.
- **CR0 update is unconditional.** Unlike XO-form `Rc=1` instructions, `addic.` always updates `CR0` from the result; the `.` is part of the mnemonic itself.
- **Common idiom: `addic. rN, rN, -1`** — decrements `rN` and sets `CR0[EQ]` when it reaches zero, in a single instruction. Frequently used as a loop counter (often paired with `bne+ loop`).
- **`XER[CA]` written same as [`addic`](addic.md).** The carry-out from the unsigned 64-bit add is recorded; the `.` only adds the CR update on top.
- **64-bit CR update on Xenon, 32-bit in xenia-rs.** [`interpreter.rs:65`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L65) computes `result as i32 as i64`; spec demands a full 64-bit compare-to-zero. The truncation is a documented xenia-rs quirk shared with the rest of the carrying-add family.
- **`SIMM` is sign-extended** to 64 bits before the add — `addic. r3, r4, -1` adds `~0` and never sets `CR0[EQ]` unless `r4 == 1`.

## Related Instructions

- [`addic`](addic.md) — same op without the CR0 update.
- [`addi`](addi.md), [`addis`](addis.md) — immediate adds without `XER[CA]`.
- [`addcx`](addcx.md) — XO-form register equivalent.
- [`subfic`](subfic.md) — `RT ← SIMM − RA` with `XER[CA]` (no record form exists).
- [`cmpi`](cmpi.md) — explicit immediate compare when the carry side-effect would be unwanted.

## IBM Reference

- [AIX 7.3 — `addic.` (Add Immediate Carrying and Record)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-addic-add-immediate-carrying-record-instruction)