ceph/src/civetweb/src/third_party/duktape-1.3.0/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 /* 'magic' constants for Murmurhash2 */
  13 #define DUK__MAGIC_M  ((duk_uint32_t) 0x5bd1e995UL)
  14 #define DUK__MAGIC_R  24
  15
  16 DUK_INTERNAL duk_uint32_t duk_util_hashbytes(const duk_uint8_t *data, duk_size_t len, duk_uint32_t seed) {
  17         duk_uint32_t h = seed ^ ((duk_uint32_t) len);
  18
  19         while (len >= 4) {
  20                 /* Portability workaround is required for platforms without
  21                  * unaligned access.  The replacement code emulates little
  22                  * endian access even on big endian architectures, which is
  23                  * OK as long as it is consistent for a build.
  24                  */
  25 #ifdef DUK_USE_HASHBYTES_UNALIGNED_U32_ACCESS
  26                 duk_uint32_t k = *((duk_uint32_t *) (void *) data);
  27 #else
  28                 duk_uint32_t k = ((duk_uint32_t) data[0]) |
  29                                  (((duk_uint32_t) data[1]) << 8) |
  30                                  (((duk_uint32_t) data[2]) << 16) |
  31                                  (((duk_uint32_t) data[3]) << 24);
  32 #endif
  33
  34                 k *= DUK__MAGIC_M;
  35                 k ^= k >> DUK__MAGIC_R;
  36                 k *= DUK__MAGIC_M;
  37                 h *= DUK__MAGIC_M;
  38                 h ^= k;
  39                 data += 4;
  40                 len -= 4;
  41         }
  42
  43         switch (len) {
  44         case 3: h ^= data[2] << 16;
  45         case 2: h ^= data[1] << 8;
  46         case 1: h ^= data[0];
  47                 h *= DUK__MAGIC_M;
  48         }
  49
  50         h ^= h >> 13;
  51         h *= DUK__MAGIC_M;
  52         h ^= h >> 15;
  53
  54         return h;
  55 }