Get 32-bit hash value from boost::hash

Question

I am using boost::hash to get hash value for a string. But it is giving different hash values for same string on Windows 32-bit and Debian 64-bit systems.

S

Answer 1

Hash-function above is simple, but weak and vulnerable.

For example, pass to that function string like "bb" "bbbb" "bbddbb" "ddffbb" -- any combination of pairs symbols with even ASCII codes, and watch for low byte. It always will be 57.

Rather, I recommend to use my hash function, which is relative lightweight, and does not have easy vulnerabilities:

#define NLF(h, c) (rand[(uint8_t)(c ^ h)])
uint32_t rand[0x100] = { 256 random non-equal values };

uint32_t oleg_h(const char *key) {
  uint32_t h = 0x1F351F35;
  char c;
  while(c = *key++)
    h = ((h >> 11) | (h << (32 - 11))) + NLF(h, c);
  h ^= h >> 16;
  return h ^ (h >> 8);
}