Organize the engine/ directory

This is an informed attempt at reorganizing the engine/ directory by
creating categorized subdirectories, in order to make it easier to
navigate and find things.

The directories created are as follows:
* engine/game: Contains all "minigames", things like the unown puzzle
and slot machine.
* engine/gfx: Contains all handling of graphics. From loading palettes
to playing animations.
* engine/link: Contains all multiplayer functionality.
* engine/menu: Contains all generic/misc. menus and menu code.
Other, more specialized menus are in their own subdirectories (pokedex,
pokegear, party menu, etc).
* engine/overworld: Contains all handling of the overworld. From loading
and connecting maps to wild encounters and the scripting engine.
* engine/pokegear: In the same vein as engine/pokedex, except it could
use some more splitting up.
* engine/pokemon: Contains everything related to manipulating pokemon
data. From the pokemon storage system to evolution and mail.
* engine/printer: Contains everything related to printing things as well
as the printer communication.
* engine/title: Contains intro sequences, title screens and credits.

1 files changed, 162 insertions, 0 deletions

diff --git a/engine/pokemon/experience.asm b/engine/pokemon/experience.asm
new file mode 100644
index 000000000..6b94ed357
--- /dev/null
+++ b/engine/pokemon/experience.asm
@@ -0,0 +1,162 @@
+CalcLevel: ; 50e1b
+	ld a, [wTempMonSpecies]
+	ld [wCurSpecies], a
+	call GetBaseData
+	ld d, 1
+.next_level
+	inc d
+	ld a, d
+	cp LOW(MAX_LEVEL + 1)
+	jr z, .got_level
+	call CalcExpAtLevel
+	push hl
+	ld hl, wTempMonExp + 2
+	ld a, [hProduct + 3]
+	ld c, a
+	ld a, [hld]
+	sub c
+	ld a, [hProduct + 2]
+	ld c, a
+	ld a, [hld]
+	sbc c
+	ld a, [hProduct + 1]
+	ld c, a
+	ld a, [hl]
+	sbc c
+	pop hl
+	jr nc, .next_level
+
+.got_level
+	dec d
+	ret
+
+CalcExpAtLevel: ; 50e47
+; (a/b)*n**3 + c*n**2 + d*n - e
+	ld a, [wBaseGrowthRate]
+	add a
+	add a
+	ld c, a
+	ld b, 0
+	ld hl, GrowthRates
+	add hl, bc
+; Cube the level
+	call .LevelSquared
+	ld a, d
+	ld [hMultiplier], a
+	call Multiply
+
+; Multiply by a
+	ld a, [hl]
+	and $f0
+	swap a
+	ld [hMultiplier], a
+	call Multiply
+; Divide by b
+	ld a, [hli]
+	and $f
+	ld [hDivisor], a
+	ld b, 4
+	call Divide
+; Push the cubic term to the stack
+	ld a, [hQuotient + 0]
+	push af
+	ld a, [hQuotient + 1]
+	push af
+	ld a, [hQuotient + 2]
+	push af
+; Square the level and multiply by the lower 7 bits of c
+	call .LevelSquared
+	ld a, [hl]
+	and $7f
+	ld [hMultiplier], a
+	call Multiply
+; Push the absolute value of the quadratic term to the stack
+	ld a, [hProduct + 1]
+	push af
+	ld a, [hProduct + 2]
+	push af
+	ld a, [hProduct + 3]
+	push af
+	ld a, [hli]
+	push af
+; Multiply the level by d
+	xor a
+	ld [hMultiplicand + 0], a
+	ld [hMultiplicand + 1], a
+	ld a, d
+	ld [hMultiplicand + 2], a
+	ld a, [hli]
+	ld [hMultiplier], a
+	call Multiply
+; Subtract e
+	ld b, [hl]
+	ld a, [hProduct + 3]
+	sub b
+	ld [hMultiplicand + 2], a
+	ld b, $0
+	ld a, [hProduct + 2]
+	sbc b
+	ld [hMultiplicand + 1], a
+	ld a, [hProduct + 1]
+	sbc b
+	ld [hMultiplicand], a
+; If bit 7 of c is set, c is negative; otherwise, it's positive
+	pop af
+	and $80
+	jr nz, .subtract
+; Add c*n**2 to (d*n - e)
+	pop bc
+	ld a, [hProduct + 3]
+	add b
+	ld [hMultiplicand + 2], a
+	pop bc
+	ld a, [hProduct + 2]
+	adc b
+	ld [hMultiplicand + 1], a
+	pop bc
+	ld a, [hProduct + 1]
+	adc b
+	ld [hMultiplicand], a
+	jr .done_quadratic
+
+.subtract
+; Subtract c*n**2 from (d*n - e)
+	pop bc
+	ld a, [hProduct + 3]
+	sub b
+	ld [hMultiplicand + 2], a
+	pop bc
+	ld a, [hProduct + 2]
+	sbc b
+	ld [hMultiplicand + 1], a
+	pop bc
+	ld a, [hProduct + 1]
+	sbc b
+	ld [hMultiplicand], a
+
+.done_quadratic
+; Add (a/b)*n**3 to (d*n - e +/- c*n**2)
+	pop bc
+	ld a, [hProduct + 3]
+	add b
+	ld [hMultiplicand + 2], a
+	pop bc
+	ld a, [hProduct + 2]
+	adc b
+	ld [hMultiplicand + 1], a
+	pop bc
+	ld a, [hProduct + 1]
+	adc b
+	ld [hMultiplicand], a
+	ret
+
+.LevelSquared: ; 50eed
+	xor a
+	ld [hMultiplicand + 0], a
+	ld [hMultiplicand + 1], a
+	ld a, d
+	ld [hMultiplicand + 2], a
+	ld [hMultiplier], a
+	jp Multiply
+
+INCLUDE "data/growth_rates.asm"