# The 147 ISL built-ins

Status: ✅ table encoding, calling convention and the `ScriptPhase` state layout;
✅ ~135 of 147 handlers characterised from the disassembly; 🟡 three resolved
only partially; ❔ the interpreter-command table is only partly recovered.

Companion to [isl-bytecode](isl-bytecode.md) (the instruction encoding) and
[mission-phase-advance](../mission-phase-advance.md) (why phases hinge on these).

## ✅ Table and calling convention

`0x8227226C … 0x822724B7` is **147 big-endian absolute VAs** — no base-relative
offsets. Verified structurally: the table starts immediately after the `bctr` at
`0x82272268`, `0x8227226C + 147·4 = 0x822724B8` is exactly where the first
handler begins, and every target lies inside `sub_82272220`.

Six ids are **unused defaults** (0, 0x41–0x44, 0x7A) and about ten more are
deliberate stubs returning a constant.

Arguments do **not** live in the instruction. Every handler starts
`addi r3,r31,20 ; bl 0x82454A40` — `std::string::c_str()` — so `[phase+20]` is a
**packed operand blob**, which is what the `local[]` staging in
[isl-bytecode](isl-bytecode.md) fills.

Return codes: **0** continue, **2** yield (re-execute next frame), **3**
coroutine control. Five built-ins skip the pc advance on 2 and so genuinely
**block**: 97, 120, 137, 142, 143.

## ✅ `ScriptPhase` state layout

| offset | meaning |
|---|---|
| `+88` | **32-entry float register file** |
| `+120` | **32-entry flag register file** |
| `+160` | frame-wait counter |
| `+164` / `+176` | **int** / **double result register** |
| `+196` | phase-finished flag |
| `+232` / `+236` | code base / end-event offset |
| `+244` | **symbol table 1** base (route + message names) |
| `+272` | trigger queue |
| `+300` | 1 = not last phase, 2 = last |
| `+304…+320` | mission timer (elapsed, t0, limit, running, enabled) |
| `+324` | **runtime unit array**, indexed by **symbol table 2** index |

Per-unit record: `+4` live object (NULL = absent), `+16` state (2 = active;
1/3/4 = gone/dead/invalid), `+32/40/48` position, `+128/132` HP / max HP,
`+140` flag bitmask.

**That is the hook into the data**: blob fields indexing `[phase+244]` are
symtab-1 indices and fields indexing `[phase+324]` are symtab-2 indices — the
two tables already parsed in [mission-script-ssb](mission-script-ssb.md).

## ✅ The conditions a phase can test

| id | name | what it tests |
|---|---|---|
| **6 / 62** | `END_PHASE` / `FORCE_END_PHASE` | sets `[+196]`, with / without the end event |
| **39 / 40** | `MARK_LAST_PHASE` / `mark_not_last` | `[+300] = 2` / `1` |
| **69 / 70** | `unit_state` / `unit_alive` | a **named unit's** lifecycle state; state == 2 |
| **20 / 95** | `hp_pct_test` / `unit_hp_pct` | unit HP as a percentage of max |
| **18** | `dist_lt` | 3-D distance between two named units below a threshold |
| **24 / 72** | `squad_survival_pct` / `group_ratio_pct` | current ÷ initial squadron members × 100 |
| **56 / 94** | `unit_relation` / `is_engaged` | relation between units; is anything engaging this one |
| **33 / 34** | `global_counter0/1` | two global counters read straight into `[+164]` |
| **132–134** | player gauges | speed/boost ratios and a player byte |
| **73, 123–127** | timer family | start / resume / stop / reset / read elapsed / read limit |
| **8 / 9 / 93** | `set_flag` / `read_freg` / `clear_flag` | latch a result into the 32-entry files |
| **100 / 115** | `push_trigger` / `named_event` | the engine→script edge |

**The state machine is therefore:** a trigger fires a coroutine → the coroutine
tests one of the predicates → it latches the answer with `set_flag` → some later
thread reaches `END_PHASE`.

Two spot-checks I ran against the disassembly rather than taking on trust:

* **id 4 (`wait_s`)** — `c_str()`, `li r3,2` (yield), `lfd f0,0(r11)`,
  `stfd f0,8(r30)`: a **double** seconds value into the thread countdown. Exactly
  as described.
* **id 24 (`squad_survival_pct`)** — indexes `[phase+324]` by `[arg+4]`, rejects
  a NULL object and state 1, then calls `823011B0` (initial, packed
  `hi<<16|lo`) and `82301118` (current). Exactly as described.

## ✅ What Stage 02 actually uses — and it settles a standing question

Counting call sites in `Stage02.ssb` (`data/isl-stage02.txt`):

| built-in | sites |
|---|---|
| `unit_state` | **255** |
| `hp_pct_test` | **167** |
| `dist_lt` | **92** |
| `unit_alive` | **71** |
| `unit_relation` | **52** |
| `set_flag` / `clear_flag` / `push_trigger` | 12 each |
| `END_PHASE` / `MARK_LAST_PHASE` / `FORCE_END_PHASE` | 12 / 8 / 3 |

**Not used at all in Stage 02:** `squad_survival_pct`, `group_ratio_pct`,
`global_counter0/1`, `is_engaged`, `player_gauge*`, `prompt_yes_no`,
`deploy_and_wait`.

🔑 **So Stage 02's phases are gated on named-unit tests — destroyed / HP /
proximity — and not on any aggregate count.** The kill-counter primitives exist
in the VM (33, 34) and this mission never calls them.

That is a direct answer to the standing "does the next wave start after N kills
or after an event?" question, at least for Stage 02: **specific units, not a
number.** "Certain objectives shot down" is right; "a certain number shot down"
is not.

⚠️ Scoped to Stage 02. Other stages may well use `squad_survival_pct` — the
counting is per-file and cheap to repeat.

## ✅ A real Stage 02 condition, read end to end

With the symbol tables resolved (unit arguments are symbol-table-2 indices), the
bytecode reads as mission logic. From `Stage02.ssb` at `0xF524`
(`data/isl-stage02-conditions.txt`):

```
unit_state(1, ADN110)     objective_marker(1, 0x01, 0, 8, 0)
unit_state(1, ADN111)     objective_marker(1, 0x02, 0, 8, 0)
unit_state(1, ADN112)     objective_marker(1, 0x05, 0, 8, 0)
                          objective_marker(1, 0x3A, 1, 8, 0)
set_flag(8)
```

Three **named ADAN squadrons** are polled for lifecycle state, each with its
objective marker updated, and then **flag 8** is latched. That is the shape
[mission-phase-advance](../mission-phase-advance.md) predicted from the
disassembly alone — trigger → predicate → `set_flag` → (later) `END_PHASE` — now
seen in the mission's own code with the squadron names the roster tables already
gave us.

The 12 `END_PHASE` sites are, by contrast, **outro sequences**:
`wait_cmds_drained` → `fade_sound(3)` → `builtin85(3)` → `wait_s(3)` →
`END_PHASE` → `yield`. The *decision* is not there; the terminator is.

### ⚠️ A decode bug that hid every argument

The first version of the argument tracker only followed
`local[i] = special[0]`. But the common form is
**`set.i k=01,03` — an immediate written straight into `local[i]`** — and
missing it meant every unit predicate printed with **no arguments at all**
(`unit_state` rather than `unit_state(1, ADN110)`). The disassembly looked
complete and was silently empty where it mattered most. Both staging forms are
now handled.

## ✅ Correction: the script reads its own flags — no engine reader needed

Last iteration ended with "what reads the flag file is unknown", after an offset
search failed and a promising hit in `sub_8226D740` turned out to be a trigger
record. **The framing was wrong.** I was looking for an *engine-side* reader;
the consumer is the **script itself**, through built-in **9** (`read_freg`),
which loads `[phase+88][i]` into the double result register `[phase+176]`.

`Stage02.ssb` calls it **12 times** — the same count as `set_flag` (12) and
`clear_flag` (12). So the latch is symmetric and entirely inside the VM:

```
set_flag(i)   ->  [phase+88][i] = 1.0 , [phase+120][i] = 1
read_freg(i)  ->  [phase+176]   = [phase+88][i]
clear_flag(i) ->  zero entry i, or all 32 when the argument is -1
```

That closes the middle of the `set_flag → … → END_PHASE` chain: a condition
coroutine latches a flag, and another coroutine reads it back with `read_freg`
and branches on it.

## 🟡 `op10` + `op13` look like a switch

Seen repeatedly, e.g. at `0x5774`:

```
op13  -> 0x5448
op10  imm 4
op13  -> 0x54F0
op10  imm 5
op13  -> 0x5598
```

Consecutive small immediates each paired with their own code offset is the shape
of a **case/branch dispatch**, and `op12` is already confirmed as the
unconditional jump. **Not confirmed** — the handlers (`0x82271598` for op10,
`0x82271830` for op13) have not been read, and I am not going to name them from
a pattern alone.

## 🟡 Not settled

* **Three handlers resisted**: id 55 (`vt35`, 411 instructions, returns a float),
  id 75 (`vt52`, message/HUD-ish), id 105 (`vt73`, meaning of unit field `+600`).
* The **1024-slot interpreter-command table** is only partly recovered — 57
  slots, by simulating the constant/stack dataflow of `sub_822FE040`.
* Names here are from handler behaviour, not from symbols; `isl.py` prints a bare
  `builtinN` for anything unread rather than guessing.