reactos/lib/rtl/random.c

   1 /*
   2  * COPYRIGHT:         See COPYING in the top level directory
   3  * PROJECT:           ReactOS system libraries
   4  * PURPOSE:           Random number generator functions
   5  * FILE:              lib/rtl/random.c
   6  * PROGRAMMER:
   7  */
   8
   9 /* INCLUDES *****************************************************************/
  10
  11 #include <rtl.h>
  12
  13 #define NDEBUG
  14 #include <debug.h>
  15
  16 static ULONG SavedValue[128] =
  17    {
  18       0x4c8bc0aa, 0x4c022957, 0x2232827a, 0x2f1e7626,  /*   0 */
  19       0x7f8bdafb, 0x5c37d02a, 0x0ab48f72, 0x2f0c4ffa,  /*   4 */
  20       0x290e1954, 0x6b635f23, 0x5d3885c0, 0x74b49ff8,  /*   8 */
  21       0x5155fa54, 0x6214ad3f, 0x111e9c29, 0x242a3a09,  /*  12 */
  22       0x75932ae1, 0x40ac432e, 0x54f7ba7a, 0x585ccbd5,  /*  16 */
  23       0x6df5c727, 0x0374dad1, 0x7112b3f1, 0x735fc311,  /*  20 */
  24       0x404331a9, 0x74d97781, 0x64495118, 0x323e04be,  /*  24 */
  25       0x5974b425, 0x4862e393, 0x62389c1d, 0x28a68b82,  /*  28 */
  26       0x0f95da37, 0x7a50bbc6, 0x09b0091c, 0x22cdb7b4,  /*  32 */
  27       0x4faaed26, 0x66417ccd, 0x189e4bfa, 0x1ce4e8dd,  /*  36 */
  28       0x5274c742, 0x3bdcf4dc, 0x2d94e907, 0x32eac016,  /*  40 */
  29       0x26d33ca3, 0x60415a8a, 0x31f57880, 0x68c8aa52,  /*  44 */
  30       0x23eb16da, 0x6204f4a1, 0x373927c1, 0x0d24eb7c,  /*  48 */
  31       0x06dd7379, 0x2b3be507, 0x0f9c55b1, 0x2c7925eb,  /*  52 */
  32       0x36d67c9a, 0x42f831d9, 0x5e3961cb, 0x65d637a8,  /*  56 */
  33       0x24bb3820, 0x4d08e33d, 0x2188754f, 0x147e409e,  /*  60 */
  34       0x6a9620a0, 0x62e26657, 0x7bd8ce81, 0x11da0abb,  /*  64 */
  35       0x5f9e7b50, 0x23e444b6, 0x25920c78, 0x5fc894f0,  /*  68 */
  36       0x5e338cbb, 0x404237fd, 0x1d60f80f, 0x320a1743,  /*  72 */
  37       0x76013d2b, 0x070294ee, 0x695e243b, 0x56b177fd,  /*  76 */
  38       0x752492e1, 0x6decd52f, 0x125f5219, 0x139d2e78,  /*  80 */
  39       0x1898d11e, 0x2f7ee785, 0x4db405d8, 0x1a028a35,  /*  84 */
  40       0x63f6f323, 0x1f6d0078, 0x307cfd67, 0x3f32a78a,  /*  88 */
  41       0x6980796c, 0x462b3d83, 0x34b639f2, 0x53fce379,  /*  92 */
  42       0x74ba50f4, 0x1abc2c4b, 0x5eeaeb8d, 0x335a7a0d,  /*  96 */
  43       0x3973dd20, 0x0462d66b, 0x159813ff, 0x1e4643fd,  /* 100 */
  44       0x06bc5c62, 0x3115e3fc, 0x09101613, 0x47af2515,  /* 104 */
  45       0x4f11ec54, 0x78b99911, 0x3db8dd44, 0x1ec10b9b,  /* 108 */
  46       0x5b5506ca, 0x773ce092, 0x567be81a, 0x5475b975,  /* 112 */
  47       0x7a2cde1a, 0x494536f5, 0x34737bb4, 0x76d9750b,  /* 116 */
  48       0x2a1f6232, 0x2e49644d, 0x7dddcbe7, 0x500cebdb,  /* 120 */
  49       0x619dab9e, 0x48c626fe, 0x1cda3193, 0x52dabe9d   /* 124 */
  50    };
  51
  52
  53 /*************************************************************************
  54  * RtlRandom   [NTDLL.@]
  55  *
  56  * Generates a random number
  57  *
  58  * PARAMS
  59  *  Seed [O] The seed of the Random function
  60  *
  61  * RETURNS
  62  *  It returns a random number distributed over [0..MAXLONG-1].
  63  */
  64 /*
  65 * @implemented
  66 */
  67 ULONG NTAPI
  68 RtlRandom (IN OUT PULONG Seed)
  69 {
  70    ULONG Rand;
  71    int Pos;
  72    ULONG Result;
  73
  74    PAGED_CODE_RTL();
  75
  76    Rand = (*Seed * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
  77    *Seed = (Rand * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
  78    Pos = *Seed & 0x7f;
  79    Result = SavedValue[Pos];
  80    SavedValue[Pos] = Rand;
  81
  82    return Result;
  83 }
  84
  85 /*
  86 * @unimplemented
  87 */
  88 ULONG
  89 NTAPI
  90 RtlRandomEx(
  91         PULONG Seed
  92         )
  93 {
  94         UNIMPLEMENTED;
  95         return 0;
  96 }
  97
  98
  99
 100 /*************************************************************************
 101  * RtlUniform   [NTDLL.@]
 102  *
 103  * Generates an uniform random number
 104  *
 105  * PARAMS
 106  *  Seed [O] The seed of the Random function
 107  *
 108  * RETURNS
 109  *  It returns a random number uniformly distributed over [0..MAXLONG-1].
 110  *
 111  * NOTES
 112  *  Generates an uniform random number using D.H. Lehmer's 1948 algorithm.
 113  *  In our case the algorithm is:
 114  *
 115  *  Result = (*Seed * 0x7fffffed + 0x7fffffc3) % MAXLONG;
 116  *
 117  *  *Seed = Result;
 118  *
 119  * DIFFERENCES
 120  *  The native documentation states that the random number is
 121  *  uniformly distributed over [0..MAXLONG]. In reality the native
 122  *  function and our function return a random number uniformly
 123  *  distributed over [0..MAXLONG-1].
 124  */
 125 ULONG NTAPI
 126 RtlUniform (PULONG Seed)
 127 {
 128   ULONG Result;
 129
 130   /*
 131    * Instead of the algorithm stated above, we use the algorithm
 132    * below, which is totally equivalent (see the tests), but does
 133    * not use a division and therefore is faster.
 134    */
 135   Result = *Seed * 0xffffffed + 0x7fffffc3;
 136
 137   if (Result == 0xffffffff || Result == 0x7ffffffe)
 138     {
 139       Result = (Result + 2) & MAXLONG;
 140     }
 141   else if (Result == 0x7fffffff)
 142     {
 143       Result = 0;
 144     }
 145   else if ((Result & 0x80000000) == 0)
 146     {
 147       Result = Result + (~Result & 1);
 148     }
 149   else
 150     {
 151       Result = (Result + (Result & 1)) & MAXLONG;
 152     }
 153
 154   *Seed = Result;
 155
 156   return Result;
 157 }
 158 /* EOF */