#!/usr/bin/env python3 """ sf2-mithril.py — Shining Force II mithril weapon predictor. Everything in this file was read out of the US ROM of Shining Force II (MD5 6473b1505334ef5620d13191c18251fe) and is reproduced here so you can check it against your own copy: $001600 the 16-bit LCG seed = (seed * 13 + 7) mod 65536 value = floor(seed * range / 65536) $FFDEA4 the seed, in work RAM $021EDA the routine that picks the mithril weapon $021F62 class -> group table $021F92 group -> four (probability, item ID) pairs $FFF7A8 the queue of weapons the smith is currently forging Usage python3 sf2-mithril.py 0x44BE what you get from this seed python3 sf2-mithril.py 0x44BE MMNK ...for a Master Monk python3 sf2-mithril.py 0x44BE HERO --frames 120 python3 sf2-mithril.py --odds exhaustive odds over all seeds Read the seed from $FFDEA4 with your emulator's RAM watch while the smith's text box is open. It advances one step per frame while the box waits for you to press a button, so "wait n more frames before confirming" means "advance the seed n more steps". Public domain. Creed's Mansion — https://fraterr.github.io/Creed-s-Mansion/ """ import sys from collections import Counter MASK = 0xFFFF ITEMS = { 0x1E: "Misty Knuckles", 0x1F: "Giant Knuckles", 0x28: "Heat Axe", 0x29: "Atlas Axe", 0x2A: "Ground Axe", 0x2B: "Rune Axe", 0x34: "Buster Shot", 0x35: "Hyper Cannon", 0x36: "Grand Cannon", 0x41: "Critical Sword", 0x42: "Battle Sword", 0x44: "Counter Sword", 0x45: "Levanter", 0x50: "Valkyrie", 0x51: "Holy Lance", 0x52: "Mist Javelin", 0x53: "Halberd", 0x5F: "Great Rod", 0x60: "Supply Staff", 0x61: "Holy Staff", 0x62: "Freeze Staff", 0x63: "Goddess Staff", 0x64: "Mystery Staff", 0x6B: "Katana", 0x6C: "Ninja Katana", 0x6D: "Gisarme", } # group index -> the classes that map to it, exactly as at ROM $021F62 GROUP_CLASSES = { 0: ["HERO", "BDBT"], 1: ["PLDN", "PGNT"], 2: ["GLDT"], 3: ["WIZ", "SORC"], 4: ["VICR"], 5: ["SNIP", "BRGN", "BWNT"], 6: ["NINJ"], 7: ["MMNK"], } # group index -> four (probability parameter, item ID) pairs, ROM $021F92 GROUP_TABLE = { 0: [(16, 0x45), (8, 0x44), (4, 0x42), (1, 0x41)], 1: [(16, 0x51), (8, 0x53), (4, 0x52), (1, 0x50)], 2: [(16, 0x2B), (8, 0x2A), (4, 0x29), (1, 0x28)], 3: [(16, 0x64), (8, 0x62), (4, 0x5F), (1, 0x60)], 4: [(16, 0x64), (8, 0x63), (4, 0x5F), (1, 0x61)], 5: [(16, 0x36), (8, 0x36), (4, 0x35), (1, 0x34)], 6: [(16, 0x6D), (8, 0x6C), (4, 0x6B), (1, 0x41)], 7: [(16, 0x1F), (8, 0x1F), (4, 0x1E), (1, 0x1E)], } CLASS_TO_GROUP = {c: g for g, cs in GROUP_CLASSES.items() for c in cs} def step(seed): """One advance of the generator at ROM $001600.""" return (seed * 13 + 7) & MASK def roll(seed, rng_range): """Returns (new_seed, value) exactly as $001600 does.""" seed = step(seed) return seed, (seed * rng_range) >> 16 def choose(seed, klass=None): """ Runs the routine at $021EDA. Returns (item_id, seed_after, trace). klass is a four-letter class label. None or an unlisted label takes the coin-flip branch at $021F02, exactly as the game does. """ trace = [] group = CLASS_TO_GROUP.get(klass) if group is None: before = seed seed, v = roll(seed, 2) group = 0 if v != 0 else 2 trace.append((before, 2, v, "class not listed -> group %d" % group)) for probability, item in GROUP_TABLE[group]: before = seed seed, v = roll(seed, probability) trace.append((before, probability, v, ITEMS.get(item, "$%02X" % item))) if v == 0: return item, seed, trace return item, seed, trace def tier_of(seed, klass): """Which of the four table entries this seed lands on, 0 = best.""" group = CLASS_TO_GROUP.get(klass) if group is None: seed, v = roll(seed, 2) group = 0 if v != 0 else 2 for i, (probability, _item) in enumerate(GROUP_TABLE[group]): seed, v = roll(seed, probability) if v == 0: return i return 3 def report(seed, klass, frames): group = CLASS_TO_GROUP.get(klass) print("seed $%04X class %s group %s" % (seed, klass or "(unlisted)", group if group is not None else "decided by a coin flip")) print() item, after, trace = choose(seed, klass) print(" what happens right now") for before, rng_range, value, what in trace: mark = "<-- taken" if value == 0 else "" print(" seed $%04X Random(%2d) -> %-2d %-16s %s" % (before, rng_range, value, what, mark)) print(" result: %s seed afterwards $%04X" % (ITEMS.get(item, "$%02X" % item), after)) print() if group is None: print(" This class is not in the table, so the first roll decides") print(" between the sword group and the axe group before anything else.") print() best = GROUP_TABLE[group][0][1] if group is not None else None print(" the next %d frames of delay" % frames) hits = [] s = seed elided = False for f in range(frames): item, _, _ = choose(s, klass) top = item == best if top: hits.append(f) if f < 24 or top: print(" +%-4d seed $%04X -> %s%s" % (f, s, ITEMS.get(item, "$%02X" % item), " TOP TIER" if top else "")) elif not elided: print(" ...") elided = True s = step(s) if best is not None: print() if hits: print(" wait %d frame(s) longer before confirming to get %s." % (hits[0], ITEMS[best])) else: print(" no top-tier result within %d frames, widen the window." % frames) def odds(): print("Exhaustive walk over all 65536 possible seeds.") print() for g in sorted(GROUP_TABLE): counts = Counter() for s in range(0x10000): seed = s for i, (probability, item) in enumerate(GROUP_TABLE[g]): seed, v = roll(seed, probability) if v == 0: counts[item] += 1 break else: counts[item] += 1 print("group %d (%s)" % (g, ", ".join(GROUP_CLASSES[g]))) for item, n in counts.most_common(): print(" %-16s %8.4f%%" % (ITEMS.get(item, "$%02X" % item), 100.0 * n / 0x10000)) print() def main(argv): if "--odds" in argv: odds() return 0 if len(argv) < 2: print(__doc__.strip()) return 1 seed = int(argv[1], 0) & MASK klass = None frames = 240 rest = [a for a in argv[2:] if not a.startswith("--")] if rest: klass = rest[0].upper() if "--frames" in argv: frames = int(argv[argv.index("--frames") + 1]) report(seed, klass, frames) return 0 if __name__ == "__main__": sys.exit(main(sys.argv))