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simpleRandom.h
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1 #ifndef __SIMPLERANDOM_H__
2 #define __SIMPLERANDOM_H__
3 
4 /*
5  * After becoming frustrated with the lack of a standalone, portable,
6  * decent random number generator, I decided to make one based on a
7  * cryptographic one-way hash function. I chose MD5 since it is fast
8  * and free source was readily available. More cryptographically
9  * secure hash functions are available (e.g. SHA-1), but for the
10  * purposes of a rand/random/erand48 replacement, MD5 should be more
11  * than sufficient.
12  *
13  * MD5 takes an arbitrary amount of input and yields a 16 byte hash.
14  * This RNG continually MD5's a 16 byte digest, and uses the bottom N
15  * bits as the random number yielded, where N is just large enough to
16  * include the largest random number desired.
17  *
18  * To yield a random number between 0 and r:
19  *
20  * create mask which has enough bits to include all of r
21  * (for example, if r is 100, mask would be 0x7F)
22  *
23  * do {
24  * digest = MD5(digest)
25  * number = digest & mask
26  * } while (number > r)
27  *
28  * The digest should be loaded and saved to a disk file between
29  * invocations of a program using the RNG.
30  *
31  * Random functions appear after the included MD5 code.
32  *
33  * Send comments to: skrenta@pbm.com (Rich Skrenta)
34  */
35 
36 
37 /*****************************************************************/
38 
39 /*
40  * This code implements the MD5 message-digest algorithm.
41  * The algorithm is due to Ron Rivest. This code was
42  * written by Colin Plumb in 1993, no copyright is claimed.
43  * This code is in the public domain; do with it what you wish.
44  *
45  * Equivalent code is available from RSA Data Security, Inc.
46  * This code has been tested against that, and is equivalent,
47  * except that you don't need to include two pages of legalese
48  * with every copy.
49  *
50  * To compute the message digest of a chunk of bytes, declare an
51  * MD5Context structure, pass it to MD5Init, call MD5Update as
52  * needed on buffers full of bytes, and then call MD5Final, which
53  * will fill a supplied 16-byte array with the digest.
54  */
55 
56 
57 typedef unsigned int word32;
58 typedef unsigned char byte;
59 
60 struct xMD5Context {
61  word32 buf[4];
62  word32 bytes[2];
63  word32 in[16];
64 };
65 
66 class simpleRandom {
67 public:
68  simpleRandom();
69  simpleRandom(const int iseed);
70 
71  float gauss(const float mean, const float sigma);
72  float rnd(int low, int high);
73 
74 private:
75 
76  void byteSwap(word32 *buf, unsigned words);
77  void xMD5Init(struct xMD5Context *ctx);
78  void xMD5Update(struct xMD5Context *ctx, byte const *buf, int len);
79  void xMD5Final(byte digest[16], struct xMD5Context *ctx);
80  void xMD5Transform(word32 buf[4], word32 const in[16]);
81  void MD5(byte *dest, const byte *orig, int len);
82  void load_seed();
83 
84  unsigned int digest[4];
85 
86 };
87 #endif
88