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tdb: add Bob Jenkins lookup3 hash as helper hash.

Browse Source 
This is a better hash than the default: shipping it with tdb makes it easy
for callers to use it as the hash by passing it to tdb_open_ex().

This version taken from CCAN and modified, which took it from
http://www.burtleburtle.net/bob/c/lookup3.c.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2010-09-24 15:34:06 +09:30
parent 7afa7b8a84
commit 3258cf3f11
7 changed files with 447 additions and 18 deletions
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61
lib/tdb/ABI/tdb-1.2.5.sigs Normal file
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@ -0,0 +1,61 @@
tdb_add_flags: void (struct tdb_context *, unsigned int)
tdb_append: int (struct tdb_context *, TDB_DATA, TDB_DATA)
tdb_chainlock: int (struct tdb_context *, TDB_DATA)
tdb_chainlock_mark: int (struct tdb_context *, TDB_DATA)
tdb_chainlock_nonblock: int (struct tdb_context *, TDB_DATA)
tdb_chainlock_read: int (struct tdb_context *, TDB_DATA)
tdb_chainlock_unmark: int (struct tdb_context *, TDB_DATA)
tdb_chainunlock: int (struct tdb_context *, TDB_DATA)
tdb_chainunlock_read: int (struct tdb_context *, TDB_DATA)
tdb_check: int (struct tdb_context *, int (*)(TDB_DATA, TDB_DATA, void *), void *)
tdb_close: int (struct tdb_context *)
tdb_delete: int (struct tdb_context *, TDB_DATA)
tdb_dump_all: void (struct tdb_context *)
tdb_enable_seqnum: void (struct tdb_context *)
tdb_error: enum TDB_ERROR (struct tdb_context *)
tdb_errorstr: const char *(struct tdb_context *)
tdb_exists: int (struct tdb_context *, TDB_DATA)
tdb_fd: int (struct tdb_context *)
tdb_fetch: TDB_DATA (struct tdb_context *, TDB_DATA)
tdb_firstkey: TDB_DATA (struct tdb_context *)
tdb_freelist_size: int (struct tdb_context *)
tdb_get_flags: int (struct tdb_context *)
tdb_get_logging_private: void *(struct tdb_context *)
tdb_get_seqnum: int (struct tdb_context *)
tdb_hash_size: int (struct tdb_context *)
tdb_increment_seqnum_nonblock: void (struct tdb_context *)
tdb_jenkins_hash: unsigned int (TDB_DATA *)
tdb_lockall: int (struct tdb_context *)
tdb_lockall_mark: int (struct tdb_context *)
tdb_lockall_nonblock: int (struct tdb_context *)
tdb_lockall_read: int (struct tdb_context *)
tdb_lockall_read_nonblock: int (struct tdb_context *)
tdb_lockall_unmark: int (struct tdb_context *)
tdb_log_fn: tdb_log_func (struct tdb_context *)
tdb_map_size: size_t (struct tdb_context *)
tdb_name: const char *(struct tdb_context *)
tdb_nextkey: TDB_DATA (struct tdb_context *, TDB_DATA)
tdb_null: dptr = 0xXXXX, dsize = 0
tdb_open: struct tdb_context *(const char *, int, int, int, mode_t)
tdb_open_ex: struct tdb_context *(const char *, int, int, int, mode_t, const struct tdb_logging_context *, tdb_hash_func)
tdb_parse_record: int (struct tdb_context *, TDB_DATA, int (*)(TDB_DATA, TDB_DATA, void *), void *)
tdb_printfreelist: int (struct tdb_context *)
tdb_remove_flags: void (struct tdb_context *, unsigned int)
tdb_reopen: int (struct tdb_context *)
tdb_reopen_all: int (int)
tdb_repack: int (struct tdb_context *)
tdb_set_logging_function: void (struct tdb_context *, const struct tdb_logging_context *)
tdb_set_max_dead: void (struct tdb_context *, int)
tdb_setalarm_sigptr: void (struct tdb_context *, volatile sig_atomic_t *)
tdb_store: int (struct tdb_context *, TDB_DATA, TDB_DATA, int)
tdb_transaction_cancel: int (struct tdb_context *)
tdb_transaction_commit: int (struct tdb_context *)
tdb_transaction_prepare_commit: int (struct tdb_context *)
tdb_transaction_start: int (struct tdb_context *)
tdb_transaction_start_nonblock: int (struct tdb_context *)
tdb_traverse: int (struct tdb_context *, tdb_traverse_func, void *)
tdb_traverse_read: int (struct tdb_context *, tdb_traverse_func, void *)
tdb_unlockall: int (struct tdb_context *)
tdb_unlockall_read: int (struct tdb_context *)
tdb_validate_freelist: int (struct tdb_context *, int *)
tdb_wipe_all: int (struct tdb_context *)

380
lib/tdb/common/hash.c Normal file
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@ -0,0 +1,380 @@
/*
Unix SMB/CIFS implementation.
trivial database library
Copyright (C) Rusty Russell 2010
** NOTE! The following LGPL license applies to the tdb
** library. This does NOT imply that all of Samba is released
** under the LGPL
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 3 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, see <http://www.gnu.org/licenses/>.
*/
#include "tdb_private.h"
/* This is based on the hash algorithm from gdbm */
unsigned int tdb_old_hash(TDB_DATA *key)
{
uint32_t value; /* Used to compute the hash value. */
uint32_t i; /* Used to cycle through random values. */
/* Set the initial value from the key size. */
for (value = 0x238F13AF * key->dsize, i=0; i < key->dsize; i++)
value = (value + (key->dptr[i] << (i*5 % 24)));
return (1103515243 * value + 12345);
}
#ifndef WORDS_BIGENDIAN
# define HASH_LITTLE_ENDIAN 1
# define HASH_BIG_ENDIAN 0
#else
# define HASH_LITTLE_ENDIAN 0
# define HASH_BIG_ENDIAN 1
#endif
/*
-------------------------------------------------------------------------------
lookup3.c, by Bob Jenkins, May 2006, Public Domain.
These are functions for producing 32-bit hashes for hash table lookup.
hash_word(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
are externally useful functions. Routines to test the hash are included
if SELF_TEST is defined. You can use this free for any purpose. It's in
the public domain. It has no warranty.
You probably want to use hashlittle(). hashlittle() and hashbig()
hash byte arrays. hashlittle() is is faster than hashbig() on
little-endian machines. Intel and AMD are little-endian machines.
On second thought, you probably want hashlittle2(), which is identical to
hashlittle() except it returns two 32-bit hashes for the price of one.
You could implement hashbig2() if you wanted but I haven't bothered here.
If you want to find a hash of, say, exactly 7 integers, do
a = i1; b = i2; c = i3;
mix(a,b,c);
a += i4; b += i5; c += i6;
mix(a,b,c);
a += i7;
final(a,b,c);
then use c as the hash value. If you have a variable length array of
4-byte integers to hash, use hash_word(). If you have a byte array (like
a character string), use hashlittle(). If you have several byte arrays, or
a mix of things, see the comments above hashlittle().
Why is this so big? I read 12 bytes at a time into 3 4-byte integers,
then mix those integers. This is fast (you can do a lot more thorough
mixing with 12*3 instructions on 3 integers than you can with 3 instructions
on 1 byte), but shoehorning those bytes into integers efficiently is messy.
*/
#define hashsize(n) ((uint32_t)1<<(n))
#define hashmask(n) (hashsize(n)-1)
#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
/*
-------------------------------------------------------------------------------
mix -- mix 3 32-bit values reversibly.
This is reversible, so any information in (a,b,c) before mix() is
still in (a,b,c) after mix().
If four pairs of (a,b,c) inputs are run through mix(), or through
mix() in reverse, there are at least 32 bits of the output that
are sometimes the same for one pair and different for another pair.
This was tested for:
* pairs that differed by one bit, by two bits, in any combination
of top bits of (a,b,c), or in any combination of bottom bits of
(a,b,c).
* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
is commonly produced by subtraction) look like a single 1-bit
difference.
* the base values were pseudorandom, all zero but one bit set, or
all zero plus a counter that starts at zero.
Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
satisfy this are
4 6 8 16 19 4
9 15 3 18 27 15
14 9 3 7 17 3
Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
for "differ" defined as + with a one-bit base and a two-bit delta. I
used http://burtleburtle.net/bob/hash/avalanche.html to choose
the operations, constants, and arrangements of the variables.
This does not achieve avalanche. There are input bits of (a,b,c)
that fail to affect some output bits of (a,b,c), especially of a. The
most thoroughly mixed value is c, but it doesn't really even achieve
avalanche in c.
This allows some parallelism. Read-after-writes are good at doubling
the number of bits affected, so the goal of mixing pulls in the opposite
direction as the goal of parallelism. I did what I could. Rotates
seem to cost as much as shifts on every machine I could lay my hands
on, and rotates are much kinder to the top and bottom bits, so I used
rotates.
-------------------------------------------------------------------------------
*/
#define mix(a,b,c) \
{ \
a -= c; a ^= rot(c, 4); c += b; \
b -= a; b ^= rot(a, 6); a += c; \
c -= b; c ^= rot(b, 8); b += a; \
a -= c; a ^= rot(c,16); c += b; \
b -= a; b ^= rot(a,19); a += c; \
c -= b; c ^= rot(b, 4); b += a; \
}
/*
-------------------------------------------------------------------------------
final -- final mixing of 3 32-bit values (a,b,c) into c
Pairs of (a,b,c) values differing in only a few bits will usually
produce values of c that look totally different. This was tested for
* pairs that differed by one bit, by two bits, in any combination
of top bits of (a,b,c), or in any combination of bottom bits of
(a,b,c).
* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
is commonly produced by subtraction) look like a single 1-bit
difference.
* the base values were pseudorandom, all zero but one bit set, or
all zero plus a counter that starts at zero.
These constants passed:
14 11 25 16 4 14 24
12 14 25 16 4 14 24
and these came close:
4 8 15 26 3 22 24
10 8 15 26 3 22 24
11 8 15 26 3 22 24
-------------------------------------------------------------------------------
*/
#define final(a,b,c) \
{ \
c ^= b; c -= rot(b,14); \
a ^= c; a -= rot(c,11); \
b ^= a; b -= rot(a,25); \
c ^= b; c -= rot(b,16); \
a ^= c; a -= rot(c,4); \
b ^= a; b -= rot(a,14); \
c ^= b; c -= rot(b,24); \
}
/*
-------------------------------------------------------------------------------
hashlittle() -- hash a variable-length key into a 32-bit value
k : the key (the unaligned variable-length array of bytes)
length : the length of the key, counting by bytes
val2 : IN: can be any 4-byte value OUT: second 32 bit hash.
Returns a 32-bit value. Every bit of the key affects every bit of
the return value. Two keys differing by one or two bits will have
totally different hash values. Note that the return value is better
mixed than val2, so use that first.
The best hash table sizes are powers of 2. There is no need to do
mod a prime (mod is sooo slow!). If you need less than 32 bits,
use a bitmask. For example, if you need only 10 bits, do
h = (h & hashmask(10));
In which case, the hash table should have hashsize(10) elements.
If you are hashing n strings (uint8_t **)k, do it like this:
for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
code any way you wish, private, educational, or commercial. It's free.
Use for hash table lookup, or anything where one collision in 2^^32 is
acceptable. Do NOT use for cryptographic purposes.
-------------------------------------------------------------------------------
*/
static uint32_t hashlittle( const void *key, size_t length )
{
uint32_t a,b,c; /* internal state */
union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */
/* Set up the internal state */
a = b = c = 0xdeadbeef + ((uint32_t)length);
u.ptr = key;
if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */
#ifdef VALGRIND
const uint8_t *k8;
#endif
/*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
while (length > 12)
{
a += k[0];
b += k[1];
c += k[2];
mix(a,b,c);
length -= 12;
k += 3;
}
/*----------------------------- handle the last (probably partial) block */
/*
* "k[2]&0xffffff" actually reads beyond the end of the string, but
* then masks off the part it's not allowed to read. Because the
* string is aligned, the masked-off tail is in the same word as the
* rest of the string. Every machine with memory protection I've seen
* does it on word boundaries, so is OK with this. But VALGRIND will
* still catch it and complain. The masking trick does make the hash
* noticably faster for short strings (like English words).
*/
#ifndef VALGRIND
switch(length)
{
case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
case 8 : b+=k[1]; a+=k[0]; break;
case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
case 6 : b+=k[1]&0xffff; a+=k[0]; break;
case 5 : b+=k[1]&0xff; a+=k[0]; break;
case 4 : a+=k[0]; break;
case 3 : a+=k[0]&0xffffff; break;
case 2 : a+=k[0]&0xffff; break;
case 1 : a+=k[0]&0xff; break;
case 0 : return c; /* zero length strings require no mixing */
}
#else /* make valgrind happy */
k8 = (const uint8_t *)k;
switch(length)
{
case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
case 11: c+=((uint32_t)k8[10])<<16; /* fall through */
case 10: c+=((uint32_t)k8[9])<<8; /* fall through */
case 9 : c+=k8[8]; /* fall through */
case 8 : b+=k[1]; a+=k[0]; break;
case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */
case 6 : b+=((uint32_t)k8[5])<<8; /* fall through */
case 5 : b+=k8[4]; /* fall through */
case 4 : a+=k[0]; break;
case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */
case 2 : a+=((uint32_t)k8[1])<<8; /* fall through */
case 1 : a+=k8[0]; break;
case 0 : return c;
}
#endif /* !valgrind */
} else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
const uint8_t *k8;
/*--------------- all but last block: aligned reads and different mixing */
while (length > 12)
{
a += k[0] + (((uint32_t)k[1])<<16);
b += k[2] + (((uint32_t)k[3])<<16);
c += k[4] + (((uint32_t)k[5])<<16);
mix(a,b,c);
length -= 12;
k += 6;
}
/*----------------------------- handle the last (probably partial) block */
k8 = (const uint8_t *)k;
switch(length)
{
case 12: c+=k[4]+(((uint32_t)k[5])<<16);
b+=k[2]+(((uint32_t)k[3])<<16);
a+=k[0]+(((uint32_t)k[1])<<16);
break;
case 11: c+=((uint32_t)k8[10])<<16; /* fall through */
case 10: c+=k[4];
b+=k[2]+(((uint32_t)k[3])<<16);
a+=k[0]+(((uint32_t)k[1])<<16);
break;
case 9 : c+=k8[8]; /* fall through */
case 8 : b+=k[2]+(((uint32_t)k[3])<<16);
a+=k[0]+(((uint32_t)k[1])<<16);
break;
case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */
case 6 : b+=k[2];
a+=k[0]+(((uint32_t)k[1])<<16);
break;
case 5 : b+=k8[4]; /* fall through */
case 4 : a+=k[0]+(((uint32_t)k[1])<<16);
break;
case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */
case 2 : a+=k[0];
break;
case 1 : a+=k8[0];
break;
case 0 : return c; /* zero length requires no mixing */
}
} else { /* need to read the key one byte at a time */
const uint8_t *k = (const uint8_t *)key;
/*--------------- all but the last block: affect some 32 bits of (a,b,c) */
while (length > 12)
{
a += k[0];
a += ((uint32_t)k[1])<<8;
a += ((uint32_t)k[2])<<16;
a += ((uint32_t)k[3])<<24;
b += k[4];
b += ((uint32_t)k[5])<<8;
b += ((uint32_t)k[6])<<16;
b += ((uint32_t)k[7])<<24;
c += k[8];
c += ((uint32_t)k[9])<<8;
c += ((uint32_t)k[10])<<16;
c += ((uint32_t)k[11])<<24;
mix(a,b,c);
length -= 12;
k += 12;
}
/*-------------------------------- last block: affect all 32 bits of (c) */
switch(length) /* all the case statements fall through */
{
case 12: c+=((uint32_t)k[11])<<24;
case 11: c+=((uint32_t)k[10])<<16;
case 10: c+=((uint32_t)k[9])<<8;
case 9 : c+=k[8];
case 8 : b+=((uint32_t)k[7])<<24;
case 7 : b+=((uint32_t)k[6])<<16;
case 6 : b+=((uint32_t)k[5])<<8;
case 5 : b+=k[4];
case 4 : a+=((uint32_t)k[3])<<24;
case 3 : a+=((uint32_t)k[2])<<16;
case 2 : a+=((uint32_t)k[1])<<8;
case 1 : a+=k[0];
break;
case 0 : return c;
}
}
final(a,b,c);
return c;
}
unsigned int tdb_jenkins_hash(TDB_DATA *key)
{
return hashlittle(key->dptr, key->dsize);
}

16
lib/tdb/common/open.c
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@ -30,20 +30,6 @@
/* all contexts, to ensure no double-opens (fcntl locks don't nest!) */
static struct tdb_context *tdbs = NULL;
/* This is based on the hash algorithm from gdbm */
static unsigned int default_tdb_hash(TDB_DATA *key)
{
uint32_t value; /* Used to compute the hash value. */
uint32_t i; /* Used to cycle through random values. */
/* Set the initial value from the key size. */
for (value = 0x238F13AF * key->dsize, i=0; i < key->dsize; i++)
value = (value + (key->dptr[i] << (i*5 % 24)));
return (1103515243 * value + 12345);
}
/* We use two hashes to double-check they're using the right hash function. */
void tdb_header_hash(struct tdb_context *tdb,
uint32_t *magic1_hash, uint32_t *magic2_hash)
@ -191,7 +177,7 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
tdb->hash_fn = hash_fn;
hash_alg = "user defined";
} else {
tdb->hash_fn = default_tdb_hash;
tdb->hash_fn = tdb_old_hash;
hash_alg = "default";
}

1
lib/tdb/common/tdb_private.h
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@ -272,3 +272,4 @@ bool tdb_write_all(int fd, const void *buf, size_t count);
int tdb_transaction_recover(struct tdb_context *tdb);
void tdb_header_hash(struct tdb_context *tdb,
uint32_t *magic1_hash, uint32_t *magic2_hash);
unsigned int tdb_old_hash(TDB_DATA *key);

2
lib/tdb/configure.ac
View File

@ -2,7 +2,7 @@ AC_PREREQ(2.50)
AC_DEFUN([SMB_MODULE_DEFAULT], [echo -n ""])
AC_DEFUN([SMB_LIBRARY_ENABLE], [echo -n ""])
AC_DEFUN([SMB_ENABLE], [echo -n ""])
AC_INIT(tdb, 1.2.4)
AC_INIT(tdb, 1.2.5)
AC_CONFIG_SRCDIR([common/tdb.c])
AC_CONFIG_HEADER(include/config.h)
AC_LIBREPLACE_ALL_CHECKS

1
lib/tdb/include/tdb.h
View File

@ -142,6 +142,7 @@ _PUBLIC_ void tdb_add_flags(struct tdb_context *tdb, unsigned flag);
_PUBLIC_ void tdb_remove_flags(struct tdb_context *tdb, unsigned flag);
_PUBLIC_ void tdb_enable_seqnum(struct tdb_context *tdb);
_PUBLIC_ void tdb_increment_seqnum_nonblock(struct tdb_context *tdb);
_PUBLIC_ unsigned int tdb_jenkins_hash(TDB_DATA *key);
_PUBLIC_ int tdb_check(struct tdb_context *tdb,
int (*check) (TDB_DATA key, TDB_DATA data, void *private_data),
void *private_data);

4
lib/tdb/wscript
View File

@ -1,7 +1,7 @@
#!/usr/bin/env python
APPNAME = 'tdb'
VERSION = '1.2.4'
VERSION = '1.2.5'
blddir = 'bin'
@ -58,7 +58,7 @@ def build(bld):
COMMON_SRC = bld.SUBDIR('common',
'''check.c error.c tdb.c traverse.c
freelistcheck.c lock.c dump.c freelist.c
io.c open.c transaction.c''')
io.c open.c transaction.c hash.c''')
if not bld.CONFIG_SET('USING_SYSTEM_TDB'):
bld.SAMBA_LIBRARY('tdb',