经典计算哈希值得函数

• 经典计算哈希值得函数
  #define BITS_IN_int (sizeof(int)*CHAR_BIT)
  #define THREE_QUARTERS ((int)((BITS_IN_int 3)/4))
  #define ONE_EIGHTH ((int)(BITS_IN_int/8))
  constexpr unsigned int HIGH_BITS = (~((unsigned int)(~0) >> ONE_EIGHTH));
  unsigned int HashPJW(const char datum)
  {
  unsigned int hash_value, i;
  for (hash_value = 0; *datum; ++datum)
  {
  hash_value = (hash_value << ONE_EIGHTH) + *datum;
  if ((i = hash_value & HIGH_BITS) != 0)
  hash_value = (hash_value ^ (i >> THREE_QUARTERS)) & ~HIGH_BITS;
  }
  return hash_value;
  }
  unsigned long ElfHash(const unsigned char *name)
  {
  unsigned long h = 0, g;
  while (*name)
  {
  h = (h << 4) + *name++;
  if (g = h & 0xF0000000)
  h ^= g >> 24;
  h &= ~g;
  }
  return h;
  }