pokecrystal-board/battle/magikarp_length.asm

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2015-10-24 07:34:19 -07:00
CalcMagikarpLength: ; fbbfc
; Return Magikarp's length (in mm) at MagikarpLength (big endian).
;
; input:
; de: EnemyMonDVs
; bc: PlayerID
; This function is poorly commented.
; In short, it generates a value between 190 and 1786 using
; a Magikarp's DVs and its trainer ID. This value is further
; filtered in LoadEnemyMon to make longer Magikarp even rarer.
; The value is generated from a lookup table.
; The index is determined by the dv xored with the player's trainer id.
; bc = rrc(dv[0]) ++ rrc(dv[1]) ^ rrc(id)
; if bc < 10: [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
; bc = rrc(dv[0]) ++ rrc(dv[1]) ^ rrc(id)
; id
ld h, b
ld l, c
ld a, [hli]
ld b, a
ld c, [hl]
rrc b
rrc c
; dv
ld a, [de]
inc de
rrca
rrca
xor b
ld b, a
ld a, [de]
rrca
rrca
xor c
ld c, a
; if bc < 10:
; de = bc + 190
; break
ld a, b
and a
jr nz, .no
ld a, c
cp 10
jr nc, .no
ld hl, 190
add hl, bc
ld d, h
ld e, l
jr .done
.no
ld hl, .Lengths
ld a, 2
ld [wd265], a
.read
ld a, [hli]
ld e, a
ld a, [hli]
ld d, a
call .BCLessThanDE
jr nc, .next
; c = (bc - de) / [hl]
call .BCMinusDE
ld a, b
ld [hDividend + 0], a
ld a, c
ld [hDividend + 1], a
ld a, [hl]
ld [hDivisor], a
ld b, 2
call Divide
ld a, [hQuotient + 2]
ld c, a
; de = c + 100 * (2 + i)
xor a
ld [hMultiplicand + 0], a
ld [hMultiplicand + 1], a
ld a, 100
ld [hMultiplicand + 2], a
ld a, [wd265]
ld [hMultiplier], a
call Multiply
ld b, 0
ld a, [hProduct + 3]
add c
ld e, a
ld a, [hProduct + 2]
adc b
ld d, a
jr .done
.next
inc hl ; align to next triplet
ld a, [wd265]
inc a
ld [wd265], a
cp 16
jr c, .read
call .BCMinusDE
ld hl, 1600
add hl, bc
ld d, h
ld e, l
.done
; hl = de * 10
ld h, d
ld l, e
rept 2
add hl, hl
endr
add hl, de
add hl, hl
; hl = hl / 254
ld de, -254
ld a, -1
.div_254
inc a
add hl, de
jr c, .div_254
; d, e = hl / 12, hl % 12
ld d, 0
.mod_12
cp 12
jr c, .ok
sub 12
inc d
jr .mod_12
.ok
ld e, a
ld hl, MagikarpLength
ld [hl], d
inc hl
ld [hl], e
ret
; fbc9a
.BCLessThanDE: ; fbc9a
; Intention: Return bc < de.
; Reality: Return b < d.
ld a, b
cp d
ret c
ret nc ; whoops
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
.Lengths: ; fbca8
; ????, divisor
dwb 110, 1
dwb 310, 2
dwb 710, 4
dwb 2710, 20
dwb 7710, 50
dwb 17710, 100
dwb 32710, 150
dwb 47710, 150
dwb 57710, 100
dwb 62710, 50
dwb 64710, 20
dwb 65210, 5
dwb 65410, 2
dwb 65510, 1 ; not used
; fbcd2