/* yarandom.c -- Yet Another Random Number Generator.
- * Copyright (c) 1997, 1998, 2003 by Jamie Zawinski <jwz@jwz.org>
+ * Copyright (c) 1997-2014 by Jamie Zawinski <jwz@jwz.org>
*
* Permission to use, copy, modify, distribute, and sell this software and its
* documentation for any purpose is hereby granted without fee, provided that
#else
gettimeofday(&tp);
#endif
- /* ignore overflow */
- seed = (999*tp.tv_sec) + (1001*tp.tv_usec) + (1003 * getpid());
+ /* Since the multiplications will have a larger effect on the
+ upper bits than the lower bits, after every addition in the
+ seed, perform a bitwise rotate by an odd number, resulting
+ in a better distribution of randomness throughout the bits.
+ -- Brian Carlson, 2010.
+ */
+#define ROT(X,N) (((X)<<(N)) | ((X)>>((sizeof(unsigned int)*8)-(N))))
+ seed = (999U * (unsigned int) tp.tv_sec);
+ seed = ROT (seed, 11);
+ seed += (1001 * tp.tv_usec);
+ seed = ROT (seed, 7);
+ seed += (1003 * getpid());
+ seed = ROT (seed, 13);
}
a[0] += seed;
for (i = 1; i < VectorSize; i++)
{
- seed = a[i-1]*1001 + seed*999;
+ seed = seed*999;
+ seed = ROT (seed, 9);
+ seed += a[i-1]*1001;
+ seed = ROT (seed, 15);
a[i] += seed;
}