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/*
This is a maximally equidistributed combined Tausworthe generator
based on code from GNU Scientific Library 1.5 (30 Jun 2004)
x_n = (s1_n ^ s2_n ^ s3_n)
s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19))
s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25))
s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11))
The period of this generator is about 2^88.
From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
Generators", Mathematics of Computation, 65, 213 (1996), 203--213.
This is available on the net from L'Ecuyer's home page,
http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
There is an erratum in the paper "Tables of Maximally
Equidistributed Combined LFSR Generators", Mathematics of
Computation, 68, 225 (1999), 261--269:
http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
... the k_j most significant bits of z_j must be non-
zero, for each j. (Note: this restriction also applies to the
computer code given in [4], but was mistakenly not mentioned in
that paper.)
This affects the seeding procedure by imposing the requirement
s1 > 1, s2 > 7, s3 > 15.
*/
#include <string.h>
#include "rand.h"
#include "../hash.h"
static inline int __seed(unsigned int x, unsigned int m)
{
return (x < m) ? x + m : x;
}
static void __init_rand(struct frand_state *state, unsigned int seed)
{
int cranks = 6;
#define LCG(x, seed) ((x) * 69069 ^ (seed))
state->s1 = __seed(LCG((2^31) + (2^17) + (2^7), seed), 1);
state->s2 = __seed(LCG(state->s1, seed), 7);
state->s3 = __seed(LCG(state->s2, seed), 15);
while (cranks--)
__rand(state);
}
void init_rand(struct frand_state *state)
{
__init_rand(state, 1);
}
void init_rand_seed(struct frand_state *state, unsigned int seed)
{
__init_rand(state, seed);
}
void __fill_random_buf(void *buf, unsigned int len, unsigned long seed)
{
long *ptr = buf;
while ((void *) ptr - buf < len) {
*ptr = seed;
ptr++;
seed *= GOLDEN_RATIO_PRIME;
seed >>= 3;
}
}
unsigned long fill_random_buf(struct frand_state *fs, void *buf,
unsigned int len)
{
unsigned long r = __rand(fs);
if (sizeof(int) != sizeof(long *))
r *= (unsigned long) __rand(fs);
__fill_random_buf(buf, len, r);
return r;
}
unsigned long fill_random_buf_percentage(struct frand_state *fs, void *buf,
unsigned int percentage,
unsigned int segment, unsigned int len)
{
unsigned long r = __rand(fs);
unsigned int this_len;
if (percentage == 100) {
memset(buf, 0, len);
return 0;
}
if (segment > len)
segment = len;
if (sizeof(int) != sizeof(long *))
r *= (unsigned long) __rand(fs);
while (len) {
/*
* Fill random chunk
*/
this_len = (segment * (100 - percentage)) / 100;
if (this_len > len)
this_len = len;
__fill_random_buf(buf, this_len, r);
len -= this_len;
buf += this_len;
if (this_len > len)
this_len = len;
memset(buf, 0, this_len);
len -= this_len;
buf += this_len;
}
return r;
}
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