mirror of
https://github.com/reactos/reactos.git
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168 lines
4.8 KiB
C
168 lines
4.8 KiB
C
/*
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* COPYRIGHT: See COPYING in the top level directory
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* PROJECT: ReactOS system libraries
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* PURPOSE: Random number generator functions
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* FILE: lib/rtl/random.c
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* PROGRAMMER:
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*/
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/* INCLUDES *****************************************************************/
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#include <rtl.h>
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#define NDEBUG
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#include <debug.h>
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static ULONG SavedValue[128] =
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{
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0x4c8bc0aa, 0x4c022957, 0x2232827a, 0x2f1e7626, /* 0 */
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0x7f8bdafb, 0x5c37d02a, 0x0ab48f72, 0x2f0c4ffa, /* 4 */
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0x290e1954, 0x6b635f23, 0x5d3885c0, 0x74b49ff8, /* 8 */
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0x5155fa54, 0x6214ad3f, 0x111e9c29, 0x242a3a09, /* 12 */
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0x75932ae1, 0x40ac432e, 0x54f7ba7a, 0x585ccbd5, /* 16 */
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0x6df5c727, 0x0374dad1, 0x7112b3f1, 0x735fc311, /* 20 */
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0x404331a9, 0x74d97781, 0x64495118, 0x323e04be, /* 24 */
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0x5974b425, 0x4862e393, 0x62389c1d, 0x28a68b82, /* 28 */
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0x0f95da37, 0x7a50bbc6, 0x09b0091c, 0x22cdb7b4, /* 32 */
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0x4faaed26, 0x66417ccd, 0x189e4bfa, 0x1ce4e8dd, /* 36 */
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0x5274c742, 0x3bdcf4dc, 0x2d94e907, 0x32eac016, /* 40 */
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0x26d33ca3, 0x60415a8a, 0x31f57880, 0x68c8aa52, /* 44 */
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0x23eb16da, 0x6204f4a1, 0x373927c1, 0x0d24eb7c, /* 48 */
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0x06dd7379, 0x2b3be507, 0x0f9c55b1, 0x2c7925eb, /* 52 */
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0x36d67c9a, 0x42f831d9, 0x5e3961cb, 0x65d637a8, /* 56 */
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0x24bb3820, 0x4d08e33d, 0x2188754f, 0x147e409e, /* 60 */
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0x6a9620a0, 0x62e26657, 0x7bd8ce81, 0x11da0abb, /* 64 */
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0x5f9e7b50, 0x23e444b6, 0x25920c78, 0x5fc894f0, /* 68 */
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0x5e338cbb, 0x404237fd, 0x1d60f80f, 0x320a1743, /* 72 */
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0x76013d2b, 0x070294ee, 0x695e243b, 0x56b177fd, /* 76 */
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0x752492e1, 0x6decd52f, 0x125f5219, 0x139d2e78, /* 80 */
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0x1898d11e, 0x2f7ee785, 0x4db405d8, 0x1a028a35, /* 84 */
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0x63f6f323, 0x1f6d0078, 0x307cfd67, 0x3f32a78a, /* 88 */
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0x6980796c, 0x462b3d83, 0x34b639f2, 0x53fce379, /* 92 */
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0x74ba50f4, 0x1abc2c4b, 0x5eeaeb8d, 0x335a7a0d, /* 96 */
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0x3973dd20, 0x0462d66b, 0x159813ff, 0x1e4643fd, /* 100 */
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0x06bc5c62, 0x3115e3fc, 0x09101613, 0x47af2515, /* 104 */
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0x4f11ec54, 0x78b99911, 0x3db8dd44, 0x1ec10b9b, /* 108 */
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0x5b5506ca, 0x773ce092, 0x567be81a, 0x5475b975, /* 112 */
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0x7a2cde1a, 0x494536f5, 0x34737bb4, 0x76d9750b, /* 116 */
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0x2a1f6232, 0x2e49644d, 0x7dddcbe7, 0x500cebdb, /* 120 */
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0x619dab9e, 0x48c626fe, 0x1cda3193, 0x52dabe9d /* 124 */
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};
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/*************************************************************************
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* RtlRandom [NTDLL.@]
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*
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* Generates a random number
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*
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* PARAMS
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* Seed [O] The seed of the Random function
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*
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* RETURNS
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* It returns a random number distributed over [0..MAXLONG-1].
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*/
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/*
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* @implemented
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*/
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ULONG NTAPI
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RtlRandom (IN OUT PULONG Seed)
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{
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ULONG Rand;
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int Pos;
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ULONG Result;
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PAGED_CODE_RTL();
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Rand = (*Seed * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
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*Seed = (Rand * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
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Pos = *Seed & 0x7f;
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Result = SavedValue[Pos];
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SavedValue[Pos] = Rand;
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return Result;
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}
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/*
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* @implemented
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*/
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ULONG
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NTAPI
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RtlRandomEx( IN OUT PULONG Seed
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)
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{
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ULONG Rand;
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int Pos;
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ULONG Result;
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PAGED_CODE_RTL();
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Rand = (*Seed * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
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*Seed = (Rand * 0x7fffffed + 0x7fffffc3) % 0x7fffffff;
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Pos = *Seed & 0x7f;
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Result = SavedValue[Pos];
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SavedValue[Pos] = Rand;
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return Result;
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}
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/*************************************************************************
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* RtlUniform [NTDLL.@]
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*
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* Generates an uniform random number
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*
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* PARAMS
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* Seed [O] The seed of the Random function
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*
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* RETURNS
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* It returns a random number uniformly distributed over [0..MAXLONG-1].
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*
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* NOTES
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* Generates an uniform random number using D.H. Lehmer's 1948 algorithm.
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* In our case the algorithm is:
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*
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* Result = (*Seed * 0x7fffffed + 0x7fffffc3) % MAXLONG;
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*
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* *Seed = Result;
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*
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* DIFFERENCES
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* The native documentation states that the random number is
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* uniformly distributed over [0..MAXLONG]. In reality the native
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* function and our function return a random number uniformly
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* distributed over [0..MAXLONG-1].
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*/
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ULONG NTAPI
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RtlUniform (PULONG Seed)
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{
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ULONG Result;
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/*
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* Instead of the algorithm stated above, we use the algorithm
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* below, which is totally equivalent (see the tests), but does
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* not use a division and therefore is faster.
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*/
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Result = *Seed * 0xffffffed + 0x7fffffc3;
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if (Result == 0xffffffff || Result == 0x7ffffffe)
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{
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Result = (Result + 2) & MAXLONG;
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}
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else if (Result == 0x7fffffff)
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{
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Result = 0;
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}
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else if ((Result & 0x80000000) == 0)
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{
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Result = Result + (~Result & 1);
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}
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else
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{
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Result = (Result + (Result & 1)) & MAXLONG;
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}
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*Seed = Result;
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return Result;
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}
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/* EOF */
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