+++ /dev/null
-/* -*- Mode: C; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */
-/*
- * Hash table
- *
- * The hash function used here is by Bob Jenkins, 1996:
- * <http://burtleburtle.net/bob/hash/doobs.html>
- * "By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net.
- * You may use this code any way you wish, private, educational,
- * or commercial. It's free."
- *
- */
-#include "memcached.h"
-
-/*
- * Since the hash function does bit manipulation, it needs to know
- * whether it's big or little-endian. ENDIAN_LITTLE and ENDIAN_BIG
- * are set in the configure script.
- */
-#if ENDIAN_BIG == 1
-# define HASH_LITTLE_ENDIAN 0
-# define HASH_BIG_ENDIAN 1
-#else
-# if ENDIAN_LITTLE == 1
-# define HASH_LITTLE_ENDIAN 1
-# define HASH_BIG_ENDIAN 0
-# else
-# define HASH_LITTLE_ENDIAN 0
-# define HASH_BIG_ENDIAN 0
-# endif
-#endif
-
-#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); \
-}
-
-#if HASH_LITTLE_ENDIAN == 1
-uint32_t hash(
- const void *key, /* the key to hash */
- size_t length, /* length of the key */
- const uint32_t initval) /* initval */
-{
- 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) + initval;
-
- u.ptr = key;
- if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
- const uint32_t *k = key; /* read 32-bit chunks */
-#ifdef VALGRIND
- const uint8_t *k8;
-#endif /* ifdef VALGRIND */
-
- /*------ 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; /* zero length strings require no mixing */
- }
-
-#endif /* !valgrind */
-
- } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
- const uint16_t *k = 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; /* @fallthrough */
- case 10: c+=k[4]; /* @fallthrough@ */
- b+=k[2]+(((uint32_t)k[3])<<16);
- a+=k[0]+(((uint32_t)k[1])<<16);
- break;
- case 9 : c+=k8[8]; /* @fallthrough */
- 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; /* @fallthrough */
- case 6 : b+=k[2];
- a+=k[0]+(((uint32_t)k[1])<<16);
- break;
- case 5 : b+=k8[4]; /* @fallthrough */
- case 4 : a+=k[0]+(((uint32_t)k[1])<<16);
- break;
- case 3 : a+=((uint32_t)k8[2])<<16; /* @fallthrough */
- case 2 : a+=k[0];
- break;
- case 1 : a+=k8[0];
- break;
- case 0 : return c; /* zero length strings require no mixing */
- }
-
- } else { /* need to read the key one byte at a time */
- const uint8_t *k = 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; /* zero length strings require no mixing */
- }
- }
-
- final(a,b,c);
- return c; /* zero length strings require no mixing */
-}
-
-#elif HASH_BIG_ENDIAN == 1
-/*
- * hashbig():
- * This is the same as hashword() on big-endian machines. It is different
- * from hashlittle() on all machines. hashbig() takes advantage of
- * big-endian byte ordering.
- */
-uint32_t hash( const void *key, size_t length, const uint32_t initval)
-{
- uint32_t a,b,c;
- union { const void *ptr; size_t i; } u; /* to cast key to (size_t) happily */
-
- /* Set up the internal state */
- a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
-
- u.ptr = key;
- if (HASH_BIG_ENDIAN && ((u.i & 0x3) == 0)) {
- const uint32_t *k = key; /* read 32-bit chunks */
-#ifdef VALGRIND
- const uint8_t *k8;
-#endif /* ifdef VALGRIND */
-
- /*------ 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]<<8" actually reads beyond the end of the string, but
- * then shifts out the part it's not allowed to read. Because the
- * string is aligned, the illegal read 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]&0xffffff00; b+=k[1]; a+=k[0]; break;
- case 10: c+=k[2]&0xffff0000; b+=k[1]; a+=k[0]; break;
- case 9 : c+=k[2]&0xff000000; b+=k[1]; a+=k[0]; break;
- case 8 : b+=k[1]; a+=k[0]; break;
- case 7 : b+=k[1]&0xffffff00; a+=k[0]; break;
- case 6 : b+=k[1]&0xffff0000; a+=k[0]; break;
- case 5 : b+=k[1]&0xff000000; a+=k[0]; break;
- case 4 : a+=k[0]; break;
- case 3 : a+=k[0]&0xffffff00; break;
- case 2 : a+=k[0]&0xffff0000; break;
- case 1 : a+=k[0]&0xff000000; break;
- case 0 : return c; /* zero length strings require no mixing */
- }
-
-#else /* make valgrind happy */
-
- k8 = (const uint8_t *)k;
- switch(length) /* all the case statements fall through */
- {
- case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
- case 11: c+=((uint32_t)k8[10])<<8; /* fall through */
- case 10: c+=((uint32_t)k8[9])<<16; /* fall through */
- case 9 : c+=((uint32_t)k8[8])<<24; /* fall through */
- case 8 : b+=k[1]; a+=k[0]; break;
- case 7 : b+=((uint32_t)k8[6])<<8; /* fall through */
- case 6 : b+=((uint32_t)k8[5])<<16; /* fall through */
- case 5 : b+=((uint32_t)k8[4])<<24; /* fall through */
- case 4 : a+=k[0]; break;
- case 3 : a+=((uint32_t)k8[2])<<8; /* fall through */
- case 2 : a+=((uint32_t)k8[1])<<16; /* fall through */
- case 1 : a+=((uint32_t)k8[0])<<24; break;
- case 0 : return c;
- }
-
-#endif /* !VALGRIND */
-
- } else { /* need to read the key one byte at a time */
- const uint8_t *k = key;
-
- /*--------------- all but the last block: affect some 32 bits of (a,b,c) */
- while (length > 12)
- {
- a += ((uint32_t)k[0])<<24;
- a += ((uint32_t)k[1])<<16;
- a += ((uint32_t)k[2])<<8;
- a += ((uint32_t)k[3]);
- b += ((uint32_t)k[4])<<24;
- b += ((uint32_t)k[5])<<16;
- b += ((uint32_t)k[6])<<8;
- b += ((uint32_t)k[7]);
- c += ((uint32_t)k[8])<<24;
- c += ((uint32_t)k[9])<<16;
- c += ((uint32_t)k[10])<<8;
- c += ((uint32_t)k[11]);
- 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+=k[11];
- case 11: c+=((uint32_t)k[10])<<8;
- case 10: c+=((uint32_t)k[9])<<16;
- case 9 : c+=((uint32_t)k[8])<<24;
- case 8 : b+=k[7];
- case 7 : b+=((uint32_t)k[6])<<8;
- case 6 : b+=((uint32_t)k[5])<<16;
- case 5 : b+=((uint32_t)k[4])<<24;
- case 4 : a+=k[3];
- case 3 : a+=((uint32_t)k[2])<<8;
- case 2 : a+=((uint32_t)k[1])<<16;
- case 1 : a+=((uint32_t)k[0])<<24;
- break;
- case 0 : return c;
- }
- }
-
- final(a,b,c);
- return c;
-}
-#else /* HASH_XXX_ENDIAN == 1 */
-#error Must define HASH_BIG_ENDIAN or HASH_LITTLE_ENDIAN
-#endif /* HASH_XXX_ENDIAN == 1 */
projects / awesomized / libmemcached / blobdiff