pokecrystal-board/battle/magikarp_length.asm

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2013-02-18 01:40:01 -08:00
CalcMagikarpLength: ; fbbfc
; Return Magikarp's length (in mm) in MagikarpLength (big endian)
;
; input:
; de: EnemyMonDVs
; bc: PlayerID
; This function is needlessly convoluted, and poorly commented.
; Reading is discouraged.
; In short, it generates a value between 190 and 1786 using
; a Magikarp's DVs and its trainer ID. This value is further
; scrutinized in GetEnemyMon to make longer Magikarp even rarer.
; This is done by calculating the value using operands from
; a conversion lookup table.
; Our index is calculated by xoring DVs with the trainer ID:
; bc = rrc(rrc(dvs)) xor rrc(id)
; if bc < $a: MagikarpLength = c + 190
; if bc >= $ff00: MagikarpLength = c + 1370
; else: MagikarpLength = z*100 + (bc-x)/y
; X, Y, and Z depend on the value of b as follows:
; if b = 0: x = 310, y = 2, z = 3
; if b = 1: x = 710, y = 4, z = 4
; if b = 2-9: x = 2710, y = 20, z = 5
; if b = 10-29: x = 7710, y = 50, z = 6
; if b = 30-68: x = 17710, y = 100, z = 7
; if b = 69-126: x = 32710, y = 150, z = 8
; if b = 127-185: x = 47710, y = 150, z = 9
; if b = 186-224: x = 57710, y = 100, z = 10
; if b = 225-243: x = 62710, y = 50, z = 11
; if b = 244-251: x = 64710, y = 20, z = 12
; if b = 252-253: x = 65210, y = 5, z = 13
; if b = 254: x = 65410, y = 2, z = 14
; These values represent arbitrary conversion points.
; b = rrcrrc(atkdefdv) xor rrc(id[0])
; id
ld h, b
ld l, c
ld a, [hli]
ld b, a
ld c, [hl]
rrc b
rrc c
; dvs
ld a, [de]
inc de
rrca
rrca
xor b
ld b, a
; c = rrcrrc(spdspcdv) xor rrc(id[1])
ld a, [de]
rrca
rrca
xor c
ld c, a
; if bc < $000a:
ld a, b
and a
jr nz, .loadtable
ld a, c
cp a, $a
jr nc, .loadtable
; de = hl = bc + $be
ld hl, $be
add hl, bc
ld d, h
ld e, l
jr .endtable
.loadtable
ld hl, .MagikarpLengthTable
ld a, $02
ld [$d265], a
.readtable
ld a, [hli]
ld e, a
ld a, [hli]
ld d, a
call .BLessThanD
jr nc, .advancetable
; c = bc / [hl]
call .BCMinusDE
ld a, b
ld [$ffb3], a
ld a, c
ld [$ffb4], a
ld a, [hl]
ld [$ffb7], a
ld b, $02
call Divide
ld a, [$ffb6]
ld c, a
; de = c + 100 * (2 + number of rows down the table)
xor a
ld [$ffb4], a
ld [$ffb5], a
ld a, $64
ld [$ffb6], a
ld a, [$d265]
ld [$ffb7], a
call Multiply
ld b, $00
ld a, [$ffb6]
add c
ld e, a
ld a, [$ffb5]
adc b
ld d, a
jr .endtable
.advancetable
inc hl ; align to next triplet
ld a, [$d265]
inc a
ld [$d265], a
cp a, $10
jr c, .readtable
call .BCMinusDE
ld hl, $0640
add hl, bc
ld d, h
ld e, l
.endtable
ld h, d
ld l, e
add hl, hl
add hl, hl
add hl, de
add hl, hl ; hl = de * 10
ld de, $ff02
ld a, $ff
.loop
inc a
add hl, de ; - 254
jr c, .loop
ld d, $00
; mod $0c
.modloop
cp a, $0c
jr c, .done
sub a, $0c
inc d
jr .modloop
.done
ld e, a
ld hl, MagikarpLength
ld [hl], d
inc hl
ld [hl], e
ret
; fbc9a
.BLessThanD ; fbc9a
; return carry if b < d
ld a, b
cp d
ret c
ret nc
; fbc9e
.CLessThanE ; fbc9e
; unused
ld a, c
cp e
ret
; fbca1
.BCMinusDE ; fbca1
; bc -= de
ld a, c
sub e
ld c, a
ld a, b
sbc d
ld b, a
ret
; fbca8
.MagikarpLengthTable ; fbca8
; ????, divisor
dwb $006e, $01
dwb $0136, $02
dwb $02c6, $04
dwb $0a96, $14
dwb $1e1e, $32
dwb $452e, $64
dwb $7fc6, $96
dwb $ba5e, $96
dwb $e16e, $64
dwb $f4f6, $32
dwb $fcc6, $14
dwb $feba, $05
dwb $ff82, $02
; fbccf