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shared: use union instead of _nm_alignas() for static hash-seed

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We want the the hash-seed array is alined so it can be used both as
guint, guint32, and guint64 directly. Don't use _nm_alignas() but
instead just add the fields to the union so we get proper alignment.

While at at, also let the seed argument to c_siphash_init() be aligned
to 64 integers. c_siphash_init() does not require that, but it tries to
read the seed as (unaligned) LE 64 bit integers. So, it doesn't hurt.
This commit is contained in:
Thomas Haller
2019-05-10 08:03:54 +02:00
parent 58df3f37ea
commit 3712e7a89f
2 changed files with 12 additions and 6 deletions
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16
shared/nm-glib-aux/nm-hash-utils.c
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@@ -45,7 +45,10 @@ _get_hash_key_init (void)
* to use it as guint* or guint64* pointer. */
static union {
guint8 v8[HASH_KEY_SIZE];
} g_arr _nm_alignas (guint64);
guint _align_as_uint;
guint32 _align_as_uint32;
guint64 _align_as_uint64;
} g_arr;
const guint8 *g;
union {
guint8 v8[HASH_KEY_SIZE];
@@ -125,14 +128,17 @@ void
nm_hash_siphash42_init (CSipHash *h, guint static_seed)
{
const guint8 *g;
guint seed[HASH_KEY_SIZE_GUINT];
union {
guint64 _align_as_uint64;
guint arr[HASH_KEY_SIZE_GUINT];
} seed;
nm_assert (h);
g = _get_hash_key ();
memcpy (seed, g, HASH_KEY_SIZE);
seed[0] ^= static_seed;
c_siphash_init (h, (const guint8 *) seed);
memcpy (&seed, g, HASH_KEY_SIZE);
seed.arr[0] ^= static_seed;
c_siphash_init (h, (const guint8 *) &seed);
}
guint

2
shared/nm-glib-aux/nm-hash-utils.h
View File

@@ -34,7 +34,7 @@ void nm_hash_siphash42_init (CSipHash *h, guint static_seed);
*
* Note, that this is guaranteed to use siphash42 under the hood (contrary to
* all other NMHash API, which leave this undefined). That matters at the point,
* where the caller needs to be sure that a reasonably strong hasing algorithm
* where the caller needs to be sure that a reasonably strong hashing algorithm
* is used. (Yes, NMHash is all about siphash24, but otherwise that is not promised
* anywhere).
*