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Add zeek::max_random() & fix misuse of RAND_MAX w/ zeek::random_number()

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In deterministic mode, RAND_MAX is not related to the result of
zeek::random_number() (formerly bro_random()), but some logic was
using RAND_MAX as indication of the possible range of values.  The
new zeek::max_random() will give the correct upper-bound regardless
of whether deterministic-mode is used.
This commit is contained in:
Jon Siwek 2020-07-22 09:57:56 -07:00
parent bde38893ce
commit d486af06b1
6 changed files with 24 additions and 9 deletions
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10
src/util.cc
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@ -1183,13 +1183,21 @@ bool have_random_seed()
return bro_rand_determistic;
}
constexpr uint32_t zeek_prng_mod = 2147483647;
constexpr uint32_t zeek_prng_max = zeek_prng_mod - 1;
long int zeek::max_random()
{
return bro_rand_determistic ? zeek_prng_max : RAND_MAX;
}
long int zeek::prng(long int state)
{
// Use our own simple linear congruence PRNG to make sure we are
// predictable across platforms. (Lehmer RNG, Schrage's method)
// Note: the choice of "long int" storage type for the state is mostly
// for parity with the possible return values of random().
constexpr uint32_t m = 2147483647;
constexpr uint32_t m = zeek_prng_mod;
constexpr uint32_t a = 16807;
constexpr uint32_t q = m / a;
constexpr uint32_t r = m % a;