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00001 /*
00002  * COPYRIGHT:         See COPYING in the top level directory
00003  * PROJECT:           ReactOS system libraries
00004  * PURPOSE:           Random number generator functions
00005  * FILE:              lib/rtl/random.c
00006  * PROGRAMMER:
00007  */
00008 
00009 /* INCLUDES *****************************************************************/
00010 
00011 #include <rtl.h>
00012 
00013 #define NDEBUG
00014 #include <debug.h>
00015 
00016 static ULONG SavedValue[128] =
00017    {
00018       0x4c8bc0aa, 0x4c022957, 0x2232827a, 0x2f1e7626,  /*   0 */
00019       0x7f8bdafb, 0x5c37d02a, 0x0ab48f72, 0x2f0c4ffa,  /*   4 */
00020       0x290e1954, 0x6b635f23, 0x5d3885c0, 0x74b49ff8,  /*   8 */
00021       0x5155fa54, 0x6214ad3f, 0x111e9c29, 0x242a3a09,  /*  12 */
00022       0x75932ae1, 0x40ac432e, 0x54f7ba7a, 0x585ccbd5,  /*  16 */
00023       0x6df5c727, 0x0374dad1, 0x7112b3f1, 0x735fc311,  /*  20 */
00024       0x404331a9, 0x74d97781, 0x64495118, 0x323e04be,  /*  24 */
00025       0x5974b425, 0x4862e393, 0x62389c1d, 0x28a68b82,  /*  28 */
00026       0x0f95da37, 0x7a50bbc6, 0x09b0091c, 0x22cdb7b4,  /*  32 */
00027       0x4faaed26, 0x66417ccd, 0x189e4bfa, 0x1ce4e8dd,  /*  36 */
00028       0x5274c742, 0x3bdcf4dc, 0x2d94e907, 0x32eac016,  /*  40 */
00029       0x26d33ca3, 0x60415a8a, 0x31f57880, 0x68c8aa52,  /*  44 */
00030       0x23eb16da, 0x6204f4a1, 0x373927c1, 0x0d24eb7c,  /*  48 */
00031       0x06dd7379, 0x2b3be507, 0x0f9c55b1, 0x2c7925eb,  /*  52 */
00032       0x36d67c9a, 0x42f831d9, 0x5e3961cb, 0x65d637a8,  /*  56 */
00033       0x24bb3820, 0x4d08e33d, 0x2188754f, 0x147e409e,  /*  60 */
00034       0x6a9620a0, 0x62e26657, 0x7bd8ce81, 0x11da0abb,  /*  64 */
00035       0x5f9e7b50, 0x23e444b6, 0x25920c78, 0x5fc894f0,  /*  68 */
00036       0x5e338cbb, 0x404237fd, 0x1d60f80f, 0x320a1743,  /*  72 */
00037       0x76013d2b, 0x070294ee, 0x695e243b, 0x56b177fd,  /*  76 */
00038       0x752492e1, 0x6decd52f, 0x125f5219, 0x139d2e78,  /*  80 */
00039       0x1898d11e, 0x2f7ee785, 0x4db405d8, 0x1a028a35,  /*  84 */
00040       0x63f6f323, 0x1f6d0078, 0x307cfd67, 0x3f32a78a,  /*  88 */
00041       0x6980796c, 0x462b3d83, 0x34b639f2, 0x53fce379,  /*  92 */
00042       0x74ba50f4, 0x1abc2c4b, 0x5eeaeb8d, 0x335a7a0d,  /*  96 */
00043       0x3973dd20, 0x0462d66b, 0x159813ff, 0x1e4643fd,  /* 100 */
00044       0x06bc5c62, 0x3115e3fc, 0x09101613, 0x47af2515,  /* 104 */
00045       0x4f11ec54, 0x78b99911, 0x3db8dd44, 0x1ec10b9b,  /* 108 */
00046       0x5b5506ca, 0x773ce092, 0x567be81a, 0x5475b975,  /* 112 */
00047       0x7a2cde1a, 0x494536f5, 0x34737bb4, 0x76d9750b,  /* 116 */
00048       0x2a1f6232, 0x2e49644d, 0x7dddcbe7, 0x500cebdb,  /* 120 */
00049       0x619dab9e, 0x48c626fe, 0x1cda3193, 0x52dabe9d   /* 124 */
00050    };
00051 
00052 
00053 /*************************************************************************
00054  * RtlRandom   [NTDLL.@]
00055  *
00056  * Generates a random number
00057  *
00058  * PARAMS
00059  *  Seed [O] The seed of the Random function
00060  *
00061  * RETURNS
00062  *  It returns a random number distributed over [0..MAXLONG-1].
00063  */
00064 /*
00065 * @implemented
00066 */
00067 ULONG NTAPI
00068 RtlRandom (IN OUT PULONG Seed)
00069 {
00070    ULONG Rand;
00071    int Pos;
00072    ULONG Result;
00073 
00074    PAGED_CODE_RTL();
00075 
00076    Rand = (*Seed * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
00077    *Seed = (Rand * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
00078    Pos = *Seed & 0x7f;
00079    Result = SavedValue[Pos];
00080    SavedValue[Pos] = Rand;
00081 
00082    return Result;
00083 }
00084 
00085 /*
00086 * @implemented
00087 */
00088 ULONG
00089 NTAPI
00090 RtlRandomEx( IN OUT PULONG Seed
00091     )
00092 {
00093    ULONG Rand;
00094    int Pos;
00095    ULONG Result;
00096 
00097    PAGED_CODE_RTL();
00098 
00099    Rand = (*Seed * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
00100    *Seed = (Rand * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
00101    Pos = *Seed & 0x7f;
00102    Result = SavedValue[Pos];
00103    SavedValue[Pos] = Rand;
00104 
00105    return Result;
00106 }
00107 
00108 
00109 
00110 /*************************************************************************
00111  * RtlUniform   [NTDLL.@]
00112  *
00113  * Generates an uniform random number
00114  *
00115  * PARAMS
00116  *  Seed [O] The seed of the Random function
00117  *
00118  * RETURNS
00119  *  It returns a random number uniformly distributed over [0..MAXLONG-1].
00120  *
00121  * NOTES
00122  *  Generates an uniform random number using D.H. Lehmer's 1948 algorithm.
00123  *  In our case the algorithm is:
00124  *
00125  *  Result = (*Seed * 0x7fffffed + 0x7fffffc3) % MAXLONG;
00126  *
00127  *  *Seed = Result;
00128  *
00129  * DIFFERENCES
00130  *  The native documentation states that the random number is
00131  *  uniformly distributed over [0..MAXLONG]. In reality the native
00132  *  function and our function return a random number uniformly
00133  *  distributed over [0..MAXLONG-1].
00134  */
00135 ULONG
00136 NTAPI
00137 RtlUniform(IN PULONG Seed)
00138 {
00139     ULONG Result;
00140 
00141     /* Generate the random number */
00142     Result = (*Seed * 0x7fffffed + 0x7fffffc3) % MAXLONG;
00143 
00144     /* Return it */
00145     *Seed = Result;
00146     return Result;
00147 }
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