Decoded: OpenTTD (2003) v1.8 (2018)
Source file: random_func.hpp
Line-by-line code walkthrough by MaiZure

random_func.hpp defines Randomizer class and support fucntions

Original code:
https://github.com/MaiZure/OpenTTD-1.8/blob/master/src/core/random_func.hpp





1     COMMENT (*)
2     BLANK (-)
3     *
4     *
5     *
6     *
7     *
8     *
9     -
10    *
11    -
12    Header guard
13    Header guard
14    -
15    If we're using an Apple system...
16    *
17    Define the flag to use the builtin
18    End check for Apple
19    -
20    *
21    *
22    *
23    BLOCK START - Randomizer, stores one RNG
24    *
25    Declares an array of two 32-bit unsigned ints for state
26    -
27    Declares a Next function for getting the next random number
28    Declares another Next function to limiting the random number
29    Declares a SetSeed function to prime the RNG
30    BLOCK END - Randomizer
31    Imports one global RNG
32    Imports the other global RNG
33    *
34    *
35    BLOCK START - SaveRandomSeeds, holds randomizers
36    Declares one Randomizer storage space
37    Declares the other Randomizer storage space
38    BLOCK END - SaveRandomSeeds
39    -
40    *
41    *
42    *
43    *
44    Defines SaveRandomSeeds with one argument: the storage struct
45    BLOCK START - SaveRandomSeeds, stores the RNG state in a struct
46    Assigns the first global RNG to the storage container (by value!)
47    Assigns the second global RNG, also by value
48    BLOCK END - SaveRandomSeeds
49    -
50    *
51    *
52    *
53    *
54    Defines RestoreRandomSeeds with one argument: the storage container
55    BLOCK START - RestoreRandomSeeds, restores the saved RNG state
56    Restore the first global RNG to a previously saved value
57    Restores the second global RNG to a previously saved value
58    BLOCK END - RestoreRandomSeeds
59    -
60    Forward declares SetRandomSeed with one argument
61    If we're currently debugging the RNG
62    If this is an Apple...
63    Define the built in random function for Apple built in
64    Otherwise this isn't apple so..
65    Use another random function
66    End check for Apple
67    Declare DoRandom with two arguments, line number and file name
68    Define a RandomRange macro function as DoRandomRange
69    Forward declare DoRandomRange
70    If we're not in debug mode
71    Defines Random with no arguments
72    BLOCK START - Random, pulls a value from RNG
73    Returns a number from the RNG
74    BLOCK START - Random
75    -
76    *
77    *
78    *
79    *
80    *
81    *
82    *
83    Defines RandomRange with one argument: the upper limit
84    BLOCK START - RandomRange, returns a range-restricted number
85    Returns a number from the RNG with a limit
86    BLOCK END -RandomRange
87    End check for debug mode
88    -
89    Defines InteractiveRandom with no arguments
90    BLOCK START - InteractiveRandom, Non-game state RNG
91    Returns a value from the other RNG
92    BLOCK END - InteractiveRandom
93    -
94    Defines InteractiveRandomRange with one argument: a limit
95    BLOCK START - InteractiveRandomRange, range-restricted second RNG
96    Returns a value from the other RNG with a limit 
97    BLOCK END - InteractiveRandomRange
98    -
99    *
100   *
101   *
102   *
103   *
104   *
105   *
106   *
107   *
108   *
109   *
110   *
111   *
112   *
113   *
114   Defines Chance16I with three arguments: numerator, denominator and random
      number
115   BLOCK START - Chance16I, returns true or false based on input probability
116   Checks that b isn't zero (avoid div/0 error)
117   Checks if the random number beat the probability
118   BLOCK END - Chance16I
119   -
120   *
121   *
122   *
123   *
124   *
125   *
126   *
127   *
128   *
129   *
130   If we're debugging RNG..
131   Defines a macro for Chance16 with a random number (local scope usage)
132   End check for RNG debug mode (use a normal function)
133   Defines Chance16 with two arguments: a probability num/dem
134   BLOCK START - Chance16, returns true or false with given probability
135   Returns the value of Chance16I using RNG for an input
136   BLOCK END - Chance16
137   Ends check for random debug mode
138   -
139   *
140   *
141   *
142   *
143   *
144   *
145   *
146   *
147   *
148   *
149   *
150   *
151   *
152   *
153   *
154   If we're in random debug mode
155   Defines macro for Chance16R in terms of DoRandom
156   Ends check for debug mode
157   Defines Chance16R with with three input values: probability fraction num/dem
      and a variable to store result
158   BLOCK START - Chance16R, Gets a random number
159   Stores the random number
160   Returns the boolean roll result using the random number
161   BLOCK END - Chance16R
162   Ends check for random debug
163   -
164   Header guard