mirror of https://github.com/pret/pokecrystal.git
216 lines
3.2 KiB
NASM
216 lines
3.2 KiB
NASM
CalcMagikarpLength: ; fbbfc
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; Return Magikarp's length (in mm) at MagikarpLength (big endian).
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;
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; input:
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; de: EnemyMonDVs
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; bc: PlayerID
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; This function is poorly commented.
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; In short, it generates a value between 190 and 1786 using
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; a Magikarp's DVs and its trainer ID. This value is further
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; filtered in LoadEnemyMon to make longer Magikarp even rarer.
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; The value is generated from a lookup table.
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; The index is determined by the dv xored with the player's trainer id.
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; bc = rrc(dv[0]) ++ rrc(dv[1]) ^ rrc(id)
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; if bc < 10: [MagikarpLength] = c + 190
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; if bc >= $ff00: [MagikarpLength] = c + 1370
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; else: [MagikarpLength] = z * 100 + (bc - x) / y
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; X, Y, and Z depend on the value of b as follows:
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; if b = 0: x = 310, y = 2, z = 3
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; if b = 1: x = 710, y = 4, z = 4
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; if b = 2-9: x = 2710, y = 20, z = 5
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; if b = 10-29: x = 7710, y = 50, z = 6
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; if b = 30-68: x = 17710, y = 100, z = 7
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; if b = 69-126: x = 32710, y = 150, z = 8
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; if b = 127-185: x = 47710, y = 150, z = 9
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; if b = 186-224: x = 57710, y = 100, z = 10
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; if b = 225-243: x = 62710, y = 50, z = 11
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; if b = 244-251: x = 64710, y = 20, z = 12
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; if b = 252-253: x = 65210, y = 5, z = 13
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; if b = 254: x = 65410, y = 2, z = 14
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; bc = rrc(dv[0]) ++ rrc(dv[1]) ^ rrc(id)
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; id
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ld h, b
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ld l, c
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ld a, [hli]
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ld b, a
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ld c, [hl]
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rrc b
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rrc c
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; dv
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ld a, [de]
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inc de
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rrca
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rrca
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xor b
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ld b, a
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ld a, [de]
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rrca
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rrca
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xor c
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ld c, a
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; if bc < 10:
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; de = bc + 190
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; break
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ld a, b
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and a
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jr nz, .no
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ld a, c
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cp 10
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jr nc, .no
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ld hl, 190
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add hl, bc
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ld d, h
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ld e, l
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jr .done
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.no
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ld hl, .Lengths
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ld a, 2
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ld [wd265], a
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.read
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ld a, [hli]
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ld e, a
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ld a, [hli]
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ld d, a
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call .BCLessThanDE
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jr nc, .next
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; c = (bc - de) / [hl]
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call .BCMinusDE
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ld a, b
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ld [hDividend + 0], a
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ld a, c
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ld [hDividend + 1], a
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ld a, [hl]
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ld [hDivisor], a
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ld b, 2
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call Divide
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ld a, [hQuotient + 2]
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ld c, a
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; de = c + 100 * (2 + i)
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xor a
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ld [hMultiplicand + 0], a
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ld [hMultiplicand + 1], a
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ld a, 100
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ld [hMultiplicand + 2], a
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ld a, [wd265]
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ld [hMultiplier], a
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call Multiply
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ld b, 0
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ld a, [hProduct + 3]
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add c
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ld e, a
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ld a, [hProduct + 2]
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adc b
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ld d, a
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jr .done
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.next
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inc hl ; align to next triplet
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ld a, [wd265]
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inc a
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ld [wd265], a
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cp 16
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jr c, .read
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call .BCMinusDE
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ld hl, 1600
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add hl, bc
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ld d, h
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ld e, l
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.done
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; hl = de * 10
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ld h, d
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ld l, e
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rept 2
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add hl, hl
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endr
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add hl, de
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add hl, hl
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; hl = hl / 254
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ld de, -254
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ld a, -1
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.div_254
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inc a
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add hl, de
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jr c, .div_254
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; d, e = hl / 12, hl % 12
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ld d, 0
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.mod_12
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cp 12
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jr c, .ok
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sub 12
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inc d
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jr .mod_12
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.ok
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ld e, a
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ld hl, MagikarpLength
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ld [hl], d
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inc hl
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ld [hl], e
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ret
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; fbc9a
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.BCLessThanDE: ; fbc9a
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; Intention: Return bc < de.
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; Reality: Return b < d.
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ld a, b
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cp d
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ret c
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ret nc ; whoops
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ld a, c
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cp e
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ret
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; fbca1
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.BCMinusDE: ; fbca1
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; bc -= de
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ld a, c
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sub e
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ld c, a
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ld a, b
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sbc d
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ld b, a
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ret
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; fbca8
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.Lengths: ; fbca8
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; ????, divisor
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dwb 110, 1
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dwb 310, 2
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dwb 710, 4
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dwb 2710, 20
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dwb 7710, 50
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dwb 17710, 100
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dwb 32710, 150
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dwb 47710, 150
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dwb 57710, 100
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dwb 62710, 50
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dwb 64710, 20
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dwb 65210, 5
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dwb 65410, 2
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dwb 65510, 1 ; not used
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; fbcd2
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