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Expose Bro's linear congruence PRNG as utility function.

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It was previously not possible to crank the wheel on the PRNG in a
deterministic way without affecting the globally unique seed. The new extra
utility function bro_prng takes a state in the form of a long int and returns
the new PRNG state, now allowing arbitrary code parts to use the random number
functionality.

This commit also fixes a problem in the H3 constructor, which requires use
of multiple seeds. The single seed passed in now serves as seed to crank out as
many value needed using bro_prng.
This commit is contained in:
Matthias Vallentin 2013-06-17 14:02:14 -07:00
parent 79a6a26f9f
commit 9f74064289
3 changed files with 24 additions and 13 deletions
Download patch file Download diff file Expand all files Collapse all files

29
src/util.cc
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@ -829,22 +829,29 @@ bool have_random_seed()
return bro_rand_determistic;
}
long int bro_prng(long int state)
{
// Use our own simple linear congruence PRNG to make sure we are
// predictable across platforms.
static const long int m = 2147483647;
static const long int a = 16807;
const long int q = m / a;
const long int r = m % a;
state = a * ( state % q ) - r * ( state / q );
if ( state <= 0 )
state += m;
return state;
}
long int bro_random()
{
if ( ! bro_rand_determistic )
return random(); // Use system PRNG.
// Use our own simple linear congruence PRNG to make sure we are
// predictable across platforms.
const long int m = 2147483647;
const long int a = 16807;
const long int q = m / a;
const long int r = m % a;
bro_rand_state = a * ( bro_rand_state % q ) - r * ( bro_rand_state / q );
if ( bro_rand_state <= 0 )
bro_rand_state += m;
bro_rand_state = bro_prng(bro_rand_state);
return bro_rand_state;
}