ceph/src/civetweb/src/third_party/duktape-1.8.0/src-separate/duk_util_hashbytes.c

   1 /*
   2  *  Hash function duk_util_hashbytes().
   3  *
   4  *  Currently, 32-bit MurmurHash2.
   5  *
   6  *  Don't rely on specific hash values; hash function may be endianness
   7  *  dependent, for instance.
   8  */
   9
  10 #include "duk_internal.h"
  11
  12 #if defined(DUK_USE_STRHASH_DENSE)
  13 /* 'magic' constants for Murmurhash2 */
  14 #define DUK__MAGIC_M  ((duk_uint32_t) 0x5bd1e995UL)
  15 #define DUK__MAGIC_R  24
  16
  17 DUK_INTERNAL duk_uint32_t duk_util_hashbytes(const duk_uint8_t *data, duk_size_t len, duk_uint32_t seed) {
  18         duk_uint32_t h = seed ^ ((duk_uint32_t) len);
  19
  20         while (len >= 4) {
  21                 /* Portability workaround is required for platforms without
  22                  * unaligned access.  The replacement code emulates little
  23                  * endian access even on big endian architectures, which is
  24                  * OK as long as it is consistent for a build.
  25                  */
  26 #ifdef DUK_USE_HASHBYTES_UNALIGNED_U32_ACCESS
  27                 duk_uint32_t k = *((const duk_uint32_t *) (const void *) data);
  28 #else
  29                 duk_uint32_t k = ((duk_uint32_t) data[0]) |
  30                                  (((duk_uint32_t) data[1]) << 8) |
  31                                  (((duk_uint32_t) data[2]) << 16) |
  32                                  (((duk_uint32_t) data[3]) << 24);
  33 #endif
  34
  35                 k *= DUK__MAGIC_M;
  36                 k ^= k >> DUK__MAGIC_R;
  37                 k *= DUK__MAGIC_M;
  38                 h *= DUK__MAGIC_M;
  39                 h ^= k;
  40                 data += 4;
  41                 len -= 4;
  42         }
  43
  44         switch (len) {
  45         case 3: h ^= data[2] << 16;
  46         case 2: h ^= data[1] << 8;
  47         case 1: h ^= data[0];
  48                 h *= DUK__MAGIC_M;
  49         }
  50
  51         h ^= h >> 13;
  52         h *= DUK__MAGIC_M;
  53         h ^= h >> 15;
  54
  55         return h;
  56 }
  57 #endif  /* DUK_USE_STRHASH_DENSE */