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Document fix about AI item pointer overflowing #1066

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Aug 10, 2023
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Document fix about AI item pointer overflowing #1066

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a297d90
Document fix about AI item pointer overflowing
Idain Aug 10, 2023
41e97cb
Forgot to insert bug comment in the code
Idain Aug 10, 2023
6854485
Update docs/bugs_and_glitches.md
Idain Aug 10, 2023
7ba3c92
Apply suggestions from code review
Rangi42 Aug 10, 2023
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28 changes: 28 additions & 0 deletions docs/bugs_and_glitches.md
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,7 @@ Fixes in the [multi-player battle engine](#multi-player-battle-engine) category
- [AI makes a false assumption about `CheckTypeMatchup`](#ai-makes-a-false-assumption-about-checktypematchup)
- [AI use of Full Heal or Full Restore does not cure Nightmare status](#ai-use-of-full-heal-or-full-restore-does-not-cure-nightmare-status)
- [AI use of Full Heal does not cure confusion status](#ai-use-of-full-heal-does-not-cure-confusion-status)
- [AI might use its base reward's value as an item](#ai-might-use-its-base-rewards-value-as-an-item)
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- [Wild Pokémon can always Teleport regardless of level difference](#wild-pok%C3%A9mon-can-always-teleport-regardless-of-level-difference)
- [`RIVAL2` has lower DVs than `RIVAL1`](#rival2-has-lower-dvs-than-rival1)
- [`HELD_CATCH_CHANCE` has no effect](#held_catch_chance-has-no-effect)
Expand Down Expand Up @@ -1455,6 +1456,33 @@ Pryce's dialog ("That BADGE will raise the SPECIAL stats of POKéMON.") implies
ret
```

### AI might use its base reward's value as an item
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In the `AI_TryItem` routine, the code checks both `wEnemyTrainerItem1` and `wEnemyTrainerItem2` to see if the AI's items match any in the `AI_Items` list. However, if the AI has used its first item (or it's set to `ITEM_NONE`) and doesn't use its second item, the item pointer can overflow to the subsequent address, `wEnemyTrainerBaseReward`. If this address's value matches an item in the `AI_Items` list, the AI could mistakenly use it.
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**Fix:** Edit `AI_TryItem` in [engine/battle/ai/items.asm](https://github.com/pret/pokecrystal/blob/master/engine/battle/ai/items.asm):

```diff
AI_TryItem:
...
ld a, [wTrainerClass]
dec a
ld hl, TrainerClassAttributes + TRNATTR_AI_ITEM_SWITCH
ld bc, NUM_TRAINER_ATTRIBUTES
call AddNTimes
ld b, h
ld c, l
ld hl, AI_Items
-; BUG: AI might use its base reward's value as an item (see docs/bugs_and_glitches.md)
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- ld de, wEnemyTrainerItem1
.loop
+ ld de, wEnemyTrainerItem1
ld a, [hl]
and a
inc a
ret z
```


### Wild Pokémon can always Teleport regardless of level difference

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1 change: 1 addition & 0 deletions engine/battle/ai/items.asm
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Expand Up @@ -175,6 +175,7 @@ AI_TryItem:
ld b, h
ld c, l
ld hl, AI_Items
; BUG: AI might use its base reward's value as an item (see docs/bugs_and_glitches.md)
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ld de, wEnemyTrainerItem1
.loop
ld a, [hl]
Expand Down