tbl->entries++;
return node;
}
+
+#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.
+ -------------------------------------------------------------------------------
+*/
+
+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 */
+ const uint8_t *k8;
+
+ /*------ 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 */
+ 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;
+ }
+ } 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;
+}
git.samba.org / rsync.git / commitdiff