src/common/jhash.h

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  */
   6
   7 #ifndef _UST_COMMON_JHASH_H
   8 #define _UST_COMMON_JHASH_H
   9
  10 #include <stddef.h>
  11 #include <stdint.h>
  12 #include <urcu/compiler.h>
  13 #include <lttng/ust-endian.h>
  14
  15 /*
  16  * Hash function
  17  * Source: http://burtleburtle.net/bob/c/lookup3.c
  18  * Originally Public Domain
  19  */
  20
  21 #define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
  22
  23 #define mix(a, b, c) \
  24 do { \
  25         a -= c; a ^= rot(c,  4); c += b; \
  26         b -= a; b ^= rot(a,  6); a += c; \
  27         c -= b; c ^= rot(b,  8); b += a; \
  28         a -= c; a ^= rot(c, 16); c += b; \
  29         b -= a; b ^= rot(a, 19); a += c; \
  30         c -= b; c ^= rot(b,  4); b += a; \
  31 } while (0)
  32
  33 #define final(a, b, c) \
  34 { \
  35         c ^= b; c -= rot(b, 14); \
  36         a ^= c; a -= rot(c, 11); \
  37         b ^= a; b -= rot(a, 25); \
  38         c ^= b; c -= rot(b, 16); \
  39         a ^= c; a -= rot(c,  4);\
  40         b ^= a; b -= rot(a, 14); \
  41         c ^= b; c -= rot(b, 24); \
  42 }
  43
  44 #if (BYTE_ORDER == LITTLE_ENDIAN)
  45 #define HASH_LITTLE_ENDIAN      1
  46 #else
  47 #define HASH_LITTLE_ENDIAN      0
  48 #endif
  49
  50 /*
  51  *
  52  * hashlittle() -- hash a variable-length key into a 32-bit value
  53  *   k       : the key (the unaligned variable-length array of bytes)
  54  *   length  : the length of the key, counting by bytes
  55  *   initval : can be any 4-byte value
  56  * Returns a 32-bit value.  Every bit of the key affects every bit of
  57  * the return value.  Two keys differing by one or two bits will have
  58  * totally different hash values.
  59  *
  60  * The best hash table sizes are powers of 2.  There is no need to do
  61  * mod a prime (mod is sooo slow!).  If you need less than 32 bits,
  62  * use a bitmask.  For example, if you need only 10 bits, do
  63  *   h = (h & hashmask(10));
  64  * In which case, the hash table should have hashsize(10) elements.
  65  *
  66  * If you are hashing n strings (uint8_t **)k, do it like this:
  67  *   for (i = 0, h = 0; i < n; ++i) h = hashlittle(k[i], len[i], h);
  68  *
  69  * By Bob Jenkins, 2006.  bob_jenkins@burtleburtle.net.  You may use this
  70  * code any way you wish, private, educational, or commercial.  It's free.
  71  *
  72  * Use for hash table lookup, or anything where one collision in 2^^32 is
  73  * acceptable.  Do NOT use for cryptographic purposes.
  74  */
  75 static
  76 uint32_t hashlittle(const void *key, size_t length, uint32_t initval)
  77 {
  78         uint32_t a, b, c;       /* internal state */
  79         union {
  80                 const void *ptr;
  81                 size_t i;
  82         } u;
  83
  84         /* Set up the internal state */
  85         a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
  86
  87         u.ptr = key;
  88         if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
  89                 const uint32_t *k = (const uint32_t *) key;     /* read 32-bit chunks */
  90
  91                 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
  92                 while (length > 12) {
  93                         a += k[0];
  94                         b += k[1];
  95                         c += k[2];
  96                         mix(a, b, c);
  97                         length -= 12;
  98                         k += 3;
  99                 }
 100
 101                 /*----------------------------- handle the last (probably partial) block */
 102                 /*
 103                  * The original jhash.h reads beyond the end of string, and implements
 104                  * a special code path for VALGRIND. It seems to make ASan unhappy too
 105                  * though, so considering that hashing event names is not a fast-path
 106                  * in lttng-ust, remove the "fast" code entirely and use the slower
 107                  * but verifiable VALGRIND version of the code which does not issue
 108                  * out-of-bound reads.
 109                  */
 110                 {
 111                         const uint8_t *k8;
 112
 113                         k8 = (const uint8_t *) k;
 114                         switch (length) {
 115                         case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
 116                         case 11: c+=((uint32_t) k8[10])<<16;    /* fall through */
 117                         case 10: c+=((uint32_t) k8[9])<<8;      /* fall through */
 118                         case 9 : c+=k8[8];                      /* fall through */
 119                         case 8 : b+=k[1]; a+=k[0]; break;
 120                         case 7 : b+=((uint32_t) k8[6])<<16;     /* fall through */
 121                         case 6 : b+=((uint32_t) k8[5])<<8;      /* fall through */
 122                         case 5 : b+=k8[4];                      /* fall through */
 123                         case 4 : a+=k[0]; break;
 124                         case 3 : a+=((uint32_t) k8[2])<<16;     /* fall through */
 125                         case 2 : a+=((uint32_t) k8[1])<<8;      /* fall through */
 126                         case 1 : a+=k8[0]; break;
 127                         case 0 : return c;
 128                         }
 129                 }
 130
 131         } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
 132                 const uint16_t *k = (const uint16_t *) key;     /* read 16-bit chunks */
 133                 const uint8_t *k8;
 134
 135                 /*--------------- all but last block: aligned reads and different mixing */
 136                 while (length > 12)
 137                 {
 138                         a += k[0] + (((uint32_t) k[1])<<16);
 139                         b += k[2] + (((uint32_t) k[3])<<16);
 140                         c += k[4] + (((uint32_t) k[5])<<16);
 141                         mix(a, b, c);
 142                         length -= 12;
 143                         k += 6;
 144                 }
 145
 146                 /*----------------------------- handle the last (probably partial) block */
 147                 k8 = (const uint8_t *) k;
 148                 switch(length)
 149                 {
 150                 case 12: c+=k[4]+(((uint32_t) k[5])<<16);
 151                          b+=k[2]+(((uint32_t) k[3])<<16);
 152                          a+=k[0]+(((uint32_t) k[1])<<16);
 153                          break;
 154                 case 11: c+=((uint32_t) k8[10])<<16;    /* fall through */
 155                 case 10: c+=k[4];
 156                          b+=k[2]+(((uint32_t) k[3])<<16);
 157                          a+=k[0]+(((uint32_t) k[1])<<16);
 158                          break;
 159                 case 9 : c+=k8[8];                      /* fall through */
 160                 case 8 : b+=k[2]+(((uint32_t) k[3])<<16);
 161                          a+=k[0]+(((uint32_t) k[1])<<16);
 162                          break;
 163                 case 7 : b+=((uint32_t) k8[6])<<16;     /* fall through */
 164                 case 6 : b+=k[2];
 165                          a+=k[0]+(((uint32_t) k[1])<<16);
 166                          break;
 167                 case 5 : b+=k8[4];                      /* fall through */
 168                 case 4 : a+=k[0]+(((uint32_t) k[1])<<16);
 169                          break;
 170                 case 3 : a+=((uint32_t) k8[2])<<16;     /* fall through */
 171                 case 2 : a+=k[0];
 172                          break;
 173                 case 1 : a+=k8[0];
 174                          break;
 175                 case 0 : return c;                      /* zero length requires no mixing */
 176                 }
 177
 178         } else {                                        /* need to read the key one byte at a time */
 179                 const uint8_t *k = (const uint8_t *)key;
 180
 181                 /*--------------- all but the last block: affect some 32 bits of (a, b, c) */
 182                 while (length > 12) {
 183                         a += k[0];
 184                         a += ((uint32_t) k[1])<<8;
 185                         a += ((uint32_t) k[2])<<16;
 186                         a += ((uint32_t) k[3])<<24;
 187                         b += k[4];
 188                         b += ((uint32_t) k[5])<<8;
 189                         b += ((uint32_t) k[6])<<16;
 190                         b += ((uint32_t) k[7])<<24;
 191                         c += k[8];
 192                         c += ((uint32_t) k[9])<<8;
 193                         c += ((uint32_t) k[10])<<16;
 194                         c += ((uint32_t) k[11])<<24;
 195                         mix(a,b,c);
 196                         length -= 12;
 197                         k += 12;
 198                 }
 199
 200                 /*-------------------------------- last block: affect all 32 bits of (c) */
 201                 switch (length) {                /* all the case statements fall through */
 202                 case 12: c+=((uint32_t) k[11])<<24;     /* fall through */
 203                 case 11: c+=((uint32_t) k[10])<<16;     /* fall through */
 204                 case 10: c+=((uint32_t) k[9])<<8;       /* fall through */
 205                 case 9 : c+=k[8];                       /* fall through */
 206                 case 8 : b+=((uint32_t) k[7])<<24;      /* fall through */
 207                 case 7 : b+=((uint32_t) k[6])<<16;      /* fall through */
 208                 case 6 : b+=((uint32_t) k[5])<<8;       /* fall through */
 209                 case 5 : b+=k[4];                       /* fall through */
 210                 case 4 : a+=((uint32_t) k[3])<<24;      /* fall through */
 211                 case 3 : a+=((uint32_t) k[2])<<16;      /* fall through */
 212                 case 2 : a+=((uint32_t) k[1])<<8;       /* fall through */
 213                 case 1 : a+=k[0];
 214                          break;
 215                 case 0 : return c;
 216                 }
 217         }
 218
 219         final(a, b, c);
 220         return c;
 221 }
 222
 223 static inline
 224 uint32_t jhash(const void *key, size_t length, uint32_t seed)
 225 {
 226         return hashlittle(key, length, seed);
 227 }
 228
 229 #endif /* _UST_COMMON_JHASH_H */