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annotate pytouhou/utils/random.pyx @ 758:daa23a4ff24d

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utils: Replace custom SeekableSlice struct with std::io::Cursor.
author Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
date Tue, 05 Jan 2021 04:11:18 +0100
parents 4ce3ef053a25
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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15
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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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22
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23 It has been reverse engineered from 102h.exe."""
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25
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26 #TODO: maybe some post-processing is missing
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27
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28 cimport cython
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29 from time import time
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32 @cython.final
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33 cdef class Random:
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34 def __init__(self, long seed=-1):
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35 if seed < 0:
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36 seed = time()
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37 self.set_seed(<unsigned short>(seed & 65535))
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38
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39
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40 cdef void set_seed(self, unsigned short seed) nogil:
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41 self.seed = seed
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42 self.counter = 0
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45 cdef unsigned short rewind(self) nogil:
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46 """Rewind the PRNG by 1 step. This is the reverse of rand_uint16.
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47 Might be useful for debugging purposes.
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48 """
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49 x = self.seed
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50 x = (x >> 2) | ((x & 3) << 14)
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51 self.seed = ((x + 0x6553) & 0xffff) ^ 0x9630
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52 self.counter -= 1
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53 return self.seed
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56 cpdef unsigned short rand_uint16(self):
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57 # 102h.exe@0x41e780
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58 x = ((self.seed ^ 0x9630) - 0x6553) & 0xffff
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59 self.seed = (((x & 0xc000) >> 14) | (x << 2)) & 0xffff
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60 self.counter += 1
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61 return self.seed
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64 cpdef unsigned int rand_uint32(self):
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65 # 102h.exe@0x41e7f0
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66 a = self.rand_uint16() << 16
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67 a |= self.rand_uint16()
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68 return a
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71 cpdef double rand_double(self):
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72 # 102h.exe@0x41e820
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73 return self.rand_uint32() / <double>0x100000000