Random Numbers

Random Numbers — pseudo-random number generator

Types and Values

  GRand

Includes

#include <glib.h>

Description

The following functions allow you to use a portable, fast and good pseudo-random number generator (PRNG).

Do not use this API for cryptographic purposes such as key generation, nonces, salts or one-time pads.

This PRNG is suitable for non-cryptographic use such as in games (shuffling a card deck, generating levels), generating data for a test suite, etc. If you need random data for cryptographic purposes, it is recommended to use platform-specific APIs such as /dev/random on UNIX, or CryptGenRandom() on Windows.

GRand uses the Mersenne Twister PRNG, which was originally developed by Makoto Matsumoto and Takuji Nishimura. Further information can be found at this page.

If you just need a random number, you simply call the g_random_* functions, which will create a globally used GRand and use the according g_rand_* functions internally. Whenever you need a stream of reproducible random numbers, you better create a GRand yourself and use the g_rand_* functions directly, which will also be slightly faster. Initializing a GRand with a certain seed will produce exactly the same series of random numbers on all platforms. This can thus be used as a seed for e.g. games.

The g_rand*_range functions will return high quality equally distributed random numbers, whereas for example the (g_random_int()%max) approach often doesn't yield equally distributed numbers.

GLib changed the seeding algorithm for the pseudo-random number generator Mersenne Twister, as used by GRand. This was necessary, because some seeds would yield very bad pseudo-random streams. Also the pseudo-random integers generated by g_rand*_int_range() will have a slightly better equal distribution with the new version of GLib.

The original seeding and generation algorithms, as found in GLib 2.0.x, can be used instead of the new ones by setting the environment variable G_RANDOM_VERSION to the value of '2.0'. Use the GLib-2.0 algorithms only if you have sequences of numbers generated with Glib-2.0 that you need to reproduce exactly.

Functions

g_rand_new_with_seed ()

GRand *
g_rand_new_with_seed (guint32 seed);

Creates a new random number generator initialized with seed .

Parameters

seed

a value to initialize the random number generator

 

Returns

the new GRand


g_rand_new_with_seed_array ()

GRand *
g_rand_new_with_seed_array (const guint32 *seed,
                            guint seed_length);

Creates a new random number generator initialized with seed .

Parameters

seed

an array of seeds to initialize the random number generator

 

seed_length

an array of seeds to initialize the random number generator

 

Returns

the new GRand

Since: 2.4


g_rand_new ()

GRand *
g_rand_new (void);

Creates a new random number generator initialized with a seed taken either from /dev/urandom (if existing) or from the current time (as a fallback).

On Windows, the seed is taken from rand_s().

Returns

the new GRand


g_rand_copy ()

GRand *
g_rand_copy (GRand *rand_);

Copies a GRand into a new one with the same exact state as before. This way you can take a snapshot of the random number generator for replaying later.

Parameters

rand_

a GRand

 

Returns

the new GRand

Since: 2.4


g_rand_free ()

void
g_rand_free (GRand *rand_);

Frees the memory allocated for the GRand.

Parameters

rand_

a GRand

 

g_rand_set_seed ()

void
g_rand_set_seed (GRand *rand_,
                 guint32 seed);

Sets the seed for the random number generator GRand to seed .

Parameters

rand_

a GRand

 

seed

a value to reinitialize the random number generator

 

g_rand_set_seed_array ()

void
g_rand_set_seed_array (GRand *rand_,
                       const guint32 *seed,
                       guint seed_length);

Initializes the random number generator by an array of longs. Array can be of arbitrary size, though only the first 624 values are taken. This function is useful if you have many low entropy seeds, or if you require more then 32 bits of actual entropy for your application.

Parameters

rand_

a GRand

 

seed

array to initialize with

 

seed_length

length of array

 

Since: 2.4


g_rand_boolean()

#define             g_rand_boolean(rand_)

Returns a random gboolean from rand_ . This corresponds to a unbiased coin toss.

Parameters

rand_

a GRand

 

Returns

a random gboolean


g_rand_int ()

guint32
g_rand_int (GRand *rand_);

Returns the next random guint32 from rand_ equally distributed over the range [0..2^32-1].

Parameters

rand_

a GRand

 

Returns

a random number


g_rand_int_range ()

gint32
g_rand_int_range (GRand *rand_,
                  gint32 begin,
                  gint32 end);

Returns the next random gint32 from rand_ equally distributed over the range [begin ..end -1].

Parameters

rand_

a GRand

 

begin

lower closed bound of the interval

 

end

upper open bound of the interval

 

Returns

a random number


g_rand_double ()

gdouble
g_rand_double (GRand *rand_);

Returns the next random gdouble from rand_ equally distributed over the range [0..1).

Parameters

rand_

a GRand

 

Returns

a random number


g_rand_double_range ()

gdouble
g_rand_double_range (GRand *rand_,
                     gdouble begin,
                     gdouble end);

Returns the next random gdouble from rand_ equally distributed over the range [begin ..end ).

Parameters

rand_

a GRand

 

begin

lower closed bound of the interval

 

end

upper open bound of the interval

 

Returns

a random number


g_random_set_seed ()

void
g_random_set_seed (guint32 seed);

Sets the seed for the global random number generator, which is used by the g_random_* functions, to seed .

Parameters

seed

a value to reinitialize the global random number generator

 

g_random_boolean

#define             g_random_boolean()

Returns a random gboolean. This corresponds to a unbiased coin toss.

Returns

a random gboolean


g_random_int ()

guint32
g_random_int (void);

Return a random guint32 equally distributed over the range [0..2^32-1].

Returns

a random number


g_random_int_range ()

gint32
g_random_int_range (gint32 begin,
                    gint32 end);

Returns a random gint32 equally distributed over the range [begin ..end -1].

Parameters

begin

lower closed bound of the interval

 

end

upper open bound of the interval

 

Returns

a random number


g_random_double ()

gdouble
g_random_double (void);

Returns a random gdouble equally distributed over the range [0..1).

Returns

a random number


g_random_double_range ()

gdouble
g_random_double_range (gdouble begin,
                       gdouble end);

Returns a random gdouble equally distributed over the range [begin ..end ).

Parameters

begin

lower closed bound of the interval

 

end

upper open bound of the interval

 

Returns

a random number

Types and Values

GRand

typedef struct _GRand GRand;

The GRand struct is an opaque data structure. It should only be accessed through the g_rand_* functions.