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annotate pytouhou/utils/random.py @ 179:3c2a9e28198c

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Make rand_uint16 slighty easier to understand, and add a rewind function for debugging purposes.
author Thibaut Girka <thib@sitedethib.com>
date Sun, 23 Oct 2011 21:00:53 +0200
parents ab826bc29aa2
children
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1 # -*- encoding: utf-8 -*-
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2 ##
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3 ## Copyright (C) 2011 Thibaut Girka <thib@sitedethib.com>
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4 ##
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5 ## This program is free software; you can redistribute it and/or modify
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6 ## it under the terms of the GNU General Public License as published
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7 ## by the Free Software Foundation; version 3 only.
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8 ##
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9 ## This program is distributed in the hope that it will be useful,
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10 ## but WITHOUT ANY WARRANTY; without even the implied warranty of
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11 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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12 ## GNU General Public License for more details.
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13 ##
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16 """
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17 This file provides a pseudo-random number generator identical to the one used in
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18 Touhou 6: The Embodiment of Scarlet Devil.
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19 It is the only truly reverse-engineered piece of code of this project,
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20 as it is needed in order to retain compatibility with replay files produced by
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21 the offical game code.
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23 It has been reverse engineered from 102h.exe."""
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26 #TODO: maybe some post-processing is missing
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29 from time import time
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31 class Random(object):
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32 def __init__(self, seed=None):
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33 if seed is None:
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34 seed = int(time() % 65536)
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35 self.seed = seed
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36 self.counter = 0
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39 def set_seed(self, seed):
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40 self.seed = seed
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41 self.counter = 0
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44 def rewind(self):
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45 """Rewind the PRNG by 1 step. This is the reverse of rand_uint16.
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46 Might be useful for debugging purposes.
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47 """
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48 x = self.seed
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49 x = (x >> 2) | ((x & 3) << 14)
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50 self.seed = ((x + 0x6553) & 0xffff) ^ 0x9630
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51 self.counter -= 1
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52 return self.seed
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55 def rand_uint16(self):
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56 # 102h.exe@0x41e780
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57 x = ((self.seed ^ 0x9630) - 0x6553) & 0xffff
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58 self.seed = (((x & 0xc000) >> 14) | (x << 2)) & 0xffff
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59 self.counter += 1
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60 return self.seed
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63 def rand_uint32(self):
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64 # 102h.exe@0x41e7f0
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65 a = self.rand_uint16() << 16
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66 a |= self.rand_uint16()
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67 return a
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70 def rand_double(self):
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71 # 102h.exe@0x41e820
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72 return float(self.rand_uint32()) / 0x100000000
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