Mirror/zeek
1
0
Fork 0
mirror of https://github.com/zeek/zeek.git synced 2025-10-15 13:08:20 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 3

Expose Bro's linear congruence PRNG as utility function.

Browse source 
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

1
src/H3.h
View file

@ -72,6 +72,7 @@ public:
for ( size_t bit = 0; bit < N * CHAR_BIT; bit++ )
{
bit_lookup[bit] = 0;
seed = bro_prng(seed);
for ( size_t i = 0; i < sizeof(T)/2; i++ )
// assume random() returns at least 16 random bits
bit_lookup[bit] = (bit_lookup[bit] << 16) | (seed & 0xFFFF);

29
src/util.cc
View file

@ -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;
}

7
src/util.h
View file

@ -173,9 +173,12 @@ unsigned int initial_seed();
// Returns true if the user explicitly set a seed via init_random_seed();
extern bool have_random_seed();
// A simple linear congruence PRNG. It takes its state as argument and returns
// a new random value, which can serve as state for subsequent calls.
long int bro_prng(long int state);
// Replacement for the system random(), to which is normally falls back
// except when a seed has been given. In that case, we use our own
// predictable PRNG.
// except when a seed has been given. In that case, the function bro_prng.
long int bro_random();
// Calls the system srandom() function with the given seed if not running