AI Improvements

This fixes some of the issues with the current AI system to make them better. In short:

- Most Trainers should correctly recognise when a move is not very effective, and not use it. If they have a supereffective move and a regular-effective move, they will slightly prioritise the supereffective one, but not always use it like in regular RBY. This prevents the Lorelei softlock, for example.

- Trainers won't attempt to set status effects on Pokemon that already have one, won't try recovering at full health, and won't attempt to set up multiple Reflects or Light Screen

- Certain high-level trainers will recognise when a Pokemon does not have a status, and will try to inflict one if so. This makes Agatha's, Erika's and Koga's team types much more effective.

- Youngsters and Cue Balls no longer pick moves randomly and will actually give it some thought

- Brock and the Engineers now recognize type effectiveness, Students do not given how early they're encountered.

- General improvements to move choices for all Gym Leaders, E4 and Shinjuku Jacky.

We're almost done.

engine/battle/unused_stats_functions.asm

@@ -1,4 +1,54 @@
-; Used by the pureRGB AI
+;shinpokerednote: ADDED: doubles the given stat
+DoubleSelectedStats:
+	ldh a, [hWhoseTurn]
+	and a
+	ld a, [wPlayerStatsToDouble]
+	ld hl, wBattleMonAttack
+	jr z, .notEnemyTurn
+	ld a, [wEnemyStatsToDouble]
+	ld hl, wEnemyMonAttack
+.notEnemyTurn
+	ld c, 4
+	ld b, a
+.loop
+	srl b
+	call c, .doubleStat
+	inc hl
+	inc hl
+	dec c
+	ret z
+	jr .loop
+.doubleStat
+	push bc
+	ld a, [hli]
+	ld b, a
+	ld c, [hl] ; bc holds value of stat to double
+;double the stat
+	sla c
+	rl b
+;cap stat at 999
+	;b register contains high byte & c register contains low byte
+	ld a, c ;let's work on low byte first. Note that decimal 999 is $03E7 in hex.
+	sub 999 % $100 ;a = a - ($03E7 % $100). Gives a = a - $E7. A byte % $100 always gives the lesser nibble.
+	;Note that if a < $E7 then the carry bit 'c' in the flag register gets set due to overflowing with a negative result.
+	ld a, b ;now let's work on the high byte
+	sbc 999 / $100 ;a = a - ($03E7 / $100 + c_flag). Gives a = a - ($03 + c_flag). A byte / $100 always gives the greater nibble.
+	;Note again that if a < $03 then the carry bit remains set. 
+	;If the bit is already set from the lesser nibble, then its addition here can still make it remain set if a is low enough.
+	jr c, .donecapping ;jump to next marker if the c_flag is set. This only remains set if BC <  the cap of $03E7.
+	;else let's continue and set the 999 cap
+	ld a, 999 / $100 ; else load $03 into a
+	ld b, a ;and store it as the high byte
+	ld a, 999 % $100 ; else load $E7 into a
+	ld c, a ;and store it as the low byte
+	;now registers b & c together contain $03E7 for a capped stat value of 999
+.donecapping
+	ld a, c
+	ld [hld], a
+	ld [hl], b
+	pop bc
+	ret
+	
 ;shinpokerednote: ADDED: doubles attack if burned or quadruples speed if paralyzed.
 ;It's meant to be run right before healing paralysis or burn so as to 
 ;undo the stat changes.
@@ -31,35 +81,6 @@ UndoBurnParStats:
 	ld [de], a	;reset the stat change bits
 	ret
 
-; Reused for pureRGB AI
-DoubleSelectedStats:
-	ldh a, [hWhoseTurn]
-	and a
-	ld a, [wPlayerStatsToDouble]
-	ld hl, wBattleMonAttack + 1
-	jr z, .notEnemyTurn
-	ld a, [wEnemyStatsToDouble]
-	ld hl, wEnemyMonAttack + 1
-.notEnemyTurn
-	ld c, 4
-	ld b, a
-.loop
-	srl b
-	call c, .doubleStat
-	inc hl
-	inc hl
-	dec c
-	ret z
-	jr .loop
-.doubleStat
-	ld a, [hl]
-	add a
-	ld [hld], a
-	ld a, [hl]
-	rl a
-	ld [hli], a
-	ret
-
 ; does nothing since no stats are ever selected (barring glitches)
 ;HalveSelectedStats:
 ;	ldh a, [hWhoseTurn]