stringhash.cc

#include "stringhash.h"

#include <cstddef> // for NULL

#undef get16bits
#if (defined(__GNUC__) && defined(__i386__)) || defined(__WATCOMC__) \
  || defined(_MSC_VER) || defined (__BORLANDC__) || defined (__TURBOC__)
#define get16bits(d) (*((const uint16_t *) (d)))
#endif

#if !defined (get16bits)
#define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
                      +(uint32_t)(((const uint8_t *)(d))[0]) )
#endif

/************************************************* HASH FUNCTIONS *********************************************/

// SuperFastHash developed by Paul Hsieh.
uint32_t SuperFastHash (const char * data, int len) {
  uint32_t hash = len, tmp;
  int rem;

  if (len <= 0 || data == NULL) return 0;

  rem = len & 3;
  len >>= 2;

  /* Main loop */
  for (;len > 0; len--) {
    hash  += get16bits (data);
    tmp    = (get16bits (data+2) << 11) ^ hash;
    hash   = (hash << 16) ^ tmp;
    data  += 2*sizeof (uint16_t);
    hash  += hash >> 11;
  }

  /* Handle end cases */
  switch (rem) {
  case 3: hash += get16bits (data);
    hash ^= hash << 16;
    hash ^= ((signed char)data[sizeof (uint16_t)]) << 18;
    hash += hash >> 11;
    break;
  case 2: hash += get16bits (data);
    hash ^= hash << 11;
    hash += hash >> 17;
    break;
  case 1: hash += (signed char)*data;
    hash ^= hash << 10;
    hash += hash >> 1;
  }

  /* Force "avalanching" of final 127 bits */
  hash ^= hash << 3;
  hash += hash >> 5;
  hash ^= hash << 4;
  hash += hash >> 17;
  hash ^= hash << 25;
  hash += hash >> 6;

  return hash;
}

/************************************************* GENERIC HASH ************************************/

uint32_t vector_hash(const std::vector<int> & vec, string_hash h) {
  return h((char *)vec.data(), vec.size() * sizeof(int));
}