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/* -*- Mode: C; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4 -*- */
/* NetworkManager -- Network link manager
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301 USA.
*
* (C) Copyright 2017 Red Hat, Inc.
*/
#include "nm-default.h"
#include "nm-hash-utils.h"
#include <stdint.h>
#include "nm-shared-utils.h"
#include "nm-random-utils.h"
/*****************************************************************************/
#define HASH_KEY_SIZE 16u
#define HASH_KEY_SIZE_GUINT ((HASH_KEY_SIZE + sizeof (guint) - 1) / sizeof (guint))
G_STATIC_ASSERT (sizeof (guint) * HASH_KEY_SIZE_GUINT >= HASH_KEY_SIZE);
static const guint8 *volatile global_seed = NULL;
static const guint8 *
_get_hash_key_init (void)
{
/* the returned hash is aligned to guin64, hence, it is safe
* to use it as guint* or guint64* pointer. */
static union {
guint8 v8[HASH_KEY_SIZE];
} g_arr _nm_alignas (guint64);
static gsize g_lock;
const guint8 *g;
struct siphash siph_state;
uint64_t h;
guint *p;
g = global_seed;
if (G_LIKELY (g != NULL)) {
nm_assert (g == g_arr.v8);
return g;
}
if (g_once_init_enter (&g_lock)) {
nm_utils_random_bytes (g_arr.v8, sizeof (g_arr.v8));
/* use siphash() of the key-size, to mangle the first guint. Otherwise,
* the first guint has only the entropy that nm_utils_random_bytes()
* generated for the first 4 bytes and relies on a good random generator. */
siphash24_init (&siph_state, g_arr.v8);
siphash24_compress (g_arr.v8, sizeof (g_arr.v8), &siph_state);
h = siphash24_finalize (&siph_state);
p = (guint *) g_arr.v8;
if (sizeof (guint) < sizeof (h))
*p = *p ^ ((guint) (h & 0xFFFFFFFFu)) ^ ((guint) (h >> 32));
else
*p = *p ^ ((guint) (h & 0xFFFFFFFFu));
g_atomic_pointer_compare_and_exchange (&global_seed, NULL, g_arr.v8);
g_once_init_leave (&g_lock, 1);
}
nm_assert (global_seed == g_arr.v8);
return g_arr.v8;
}
#define _get_hash_key() \
({ \
const guint8 *_g; \
\
_g = global_seed; \
if (G_UNLIKELY (_g == NULL)) \
_g = _get_hash_key_init (); \
_g; \
})
guint
nm_hash_static (guint static_seed)
{
/* note that we only xor the static_seed with the key.
* We don't use siphash24(), which would mix the bits better.
* Note that this doesn't matter, because static_seed is not
* supposed to be a value that you are hashing (for that, use
* full siphash24()).
* Instead, different callers may set a different static_seed
* so that nm_hash_str(NULL) != nm_hash_ptr(NULL).
*
* Also, ensure that we don't return zero.
*/
return ((*((const guint *) _get_hash_key ())) ^ static_seed)
?: static_seed ?: 3679500967u;
}
void
nm_hash_init (NMHashState *state, guint static_seed)
{
const guint8 *g;
guint seed[HASH_KEY_SIZE_GUINT];
nm_assert (state);
g = _get_hash_key ();
memcpy (seed, g, HASH_KEY_SIZE);
seed[0] ^= static_seed;
siphash24_init (&state->_state, (const guint8 *) seed);
}
guint
nm_hash_str (const char *str)
{
NMHashState h;
if (!str)
return nm_hash_static (1867854211u);
nm_hash_init (&h, 1867854211u);
nm_hash_update_str (&h, str);
return nm_hash_complete (&h);
}
guint
nm_str_hash (gconstpointer str)
{
return nm_hash_str (str);
}
guint
nm_hash_ptr (gconstpointer ptr)
{
NMHashState h;
if (!ptr)
return nm_hash_static (2907677551u);
nm_hash_init (&h, 2907677551u);
nm_hash_update (&h, &ptr, sizeof (ptr));
return nm_hash_complete (&h);
}
guint
nm_direct_hash (gconstpointer ptr)
{
return nm_hash_ptr (ptr);
}
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