Specifies the type of the hash function which is passed to
g_hash_table_new() when a
GHashTable is created.
The function is passed a key and should return a #guint hash value.
hash functions which can be used when the key is a #gpointer, #gint,
and #gchar respectively.
g_direct_hash() is also the appropriate hash function for keys
of the form
GINT_TO_POINTER (n) (or similar macros).
A good hash functions should produce hash values that are evenly distributed over a fairly large range. The modulus is taken with the hash table size (a prime number) to find the ‘bucket’ to place each key into. The function should also be very fast, since it is called for each key lookup.
Note that the hash functions provided by GLib have these qualities,
but are not particularly robust against manufactured keys that
cause hash collisions. Therefore, you should consider choosing
a more secure hash function when using a GHashTable with keys
that originate in untrusted data (such as HTTP requests).
g_str_hash() in that situation might make your application
Algorithmic Complexity Attacks.
The key to choosing a good hash is unpredictability. Even cryptographic hashes are very easy to find collisions for when the remainder is taken modulo a somewhat predictable prime number. There must be an element of randomness that an attacker is unable to guess.