Fix #769: document the Heavy Ball weight bank bug

docs/bugs_and_glitches.md

@@ -46,6 +46,7 @@ Fixes in the [multi-player battle engine](#multi-player-battle-engine) category
   - [Moon Ball does not boost catch rate](#moon-ball-does-not-boost-catch-rate)
   - [Love Ball boosts catch rate for the wrong gender](#love-ball-boosts-catch-rate-for-the-wrong-gender)
   - [Fast Ball only boosts catch rate for three Pokémon](#fast-ball-only-boosts-catch-rate-for-three-pokémon)
+  - [Heavy Ball uses wrong weight value for three Pokémon](#heavy-ball-uses-wrong-weight-value-for-three-pokémon)
   - [Glacier Badge may not boost Special Defense depending on the value of Special Attack](#glacier-badge-may-not-boost-special-defense-depending-on-the-value-of-special-attack)
   - ["Smart" AI encourages Mean Look if its own Pokémon is badly poisoned](#smart-ai-encourages-mean-look-if-its-own-pokémon-is-badly-poisoned)
   - [AI makes a false assumption about `CheckTypeMatchup`](#ai-makes-a-false-assumption-about-checktypematchup)
@@ -974,6 +975,40 @@ This can occur if your party and current PC box are both full when you start the
 ```
 
 
+### Heavy Ball uses wrong weight value for three Pokémon
+
+**Fix:** Edit `GetPokedexEntryBank` in [engine/items/item_effects.asm](https://github.com/pret/pokecrystal/blob/master/engine/items/item_effects.asm):
+
+```diff
+ GetPokedexEntryBank:
+-; This function is buggy.
+-; It gets the wrong bank for Kadabra (64), Tauros (128), and Sunflora (192).
+-; Uncomment the line below to fix this.
+ 	push hl
+ 	push de
+ 	ld a, [wEnemyMonSpecies]
+-; dec a
++	dec a
+ 	rlca
+ 	rlca
+ 	maskbits NUM_DEX_ENTRY_BANKS
+ 	ld hl, .PokedexEntryBanks
+ 	ld d, 0
+ 	ld e, a
+ 	add hl, de
+ 	ld a, [hl]
+ 	pop de
+ 	pop hl
+ 	ret
+
+ .PokedexEntryBanks:
+ 	db BANK("Pokedex Entries 001-064")
+ 	db BANK("Pokedex Entries 065-128")
+ 	db BANK("Pokedex Entries 129-192")
+ 	db BANK("Pokedex Entries 193-251")
+```
+
+
 ### Glacier Badge may not boost Special Defense depending on the value of Special Attack
 
 As Pryce's dialog ("That BADGE will raise the SPECIAL stats of POKéMON.") implies, Glacier Badge is intended to boost both Special Attack and Special Defense. However, due to BoostStat overwriting `a` when boosting Special Attack, the Special Defense boost will not happen if the unboosted Special Attack stat is either 0–205 or 433–660.
@@ -2222,7 +2257,7 @@ Then create two new routines, `InvalidateSave` and `InvalidateBackupSave`:
  	jr z, .skip
 -	; jr c, .skip
 +	jr c, .skip
- 
+
  	; could have done "inc hl" instead
  	ld bc, 1
  	add hl, bc

engine/items/item_effects.asm

@@ -745,9 +745,13 @@ ParkBallMultiplier:
 	ret
 
 GetPokedexEntryBank:
+; This function is buggy.
+; It gets the wrong bank for Kadabra (64), Tauros (128), and Sunflora (192).
+; Uncomment the line below to fix this.
 	push hl
 	push de
 	ld a, [wEnemyMonSpecies]
+	; dec a
 	rlca
 	rlca
 	maskbits NUM_DEX_ENTRY_BANKS