/* This is SipHash by Jean-Philippe Aumasson and Daniel J. Bernstein.
 * The authors claim it is relatively secure compared to the alternatives
 * and that performance wise it is a suitable hash for languages like Perl.
 * See:
 *
 * https://www.131002.net/siphash/
 *
 * This implementation seems to perform slightly slower than one-at-a-time for
 * short keys, but degrades slower for longer keys. Murmur Hash outperforms it
 * regardless of keys size.
 *
 * It is 64 bit only.
 */

#ifdef CAN64BITHASH

#define SIPROUND            \
  STMT_START {              \
    v0 += v1; v1=ROTL64(v1,13); v1 ^= v0; v0=ROTL64(v0,32); \
    v2 += v3; v3=ROTL64(v3,16); v3 ^= v2;     \
    v0 += v3; v3=ROTL64(v3,21); v3 ^= v0;     \
    v2 += v1; v1=ROTL64(v1,17); v1 ^= v2; v2=ROTL64(v2,32); \
  } STMT_END

#define SIPHASH_SEED_STATE(key,v0,v1,v2,v3) \
do {                                    \
    v0 = v2 = U8TO64_LE(key + 0);       \
    v1 = v3 = U8TO64_LE(key + 8);       \
  /* "somepseudorandomlygeneratedbytes" */  \
    v0 ^= UINT64_C(0x736f6d6570736575);  \
    v1 ^= UINT64_C(0x646f72616e646f6d);      \
    v2 ^= UINT64_C(0x6c7967656e657261);      \
    v3 ^= UINT64_C(0x7465646279746573);      \
} while (0)

PERL_STATIC_INLINE
void S_perl_siphash_seed_state(const unsigned char * const seed_buf, unsigned char * state_buf) {
    U64 *v= (U64*) state_buf;
    SIPHASH_SEED_STATE(seed_buf, v[0],v[1],v[2],v[3]);
}

#define PERL_SIPHASH_FNC(FNC,SIP_ROUNDS,SIP_FINAL_ROUNDS) \
PERL_STATIC_INLINE U64 \
FNC ## _with_state_64 \
  (const unsigned char * const state, const unsigned char *in, const STRLEN inlen) \
{                                           \
  const int left = inlen & 7;               \
  const U8 *end = in + inlen - left;        \
                                            \
  U64 b = ( ( U64 )(inlen) ) << 56;         \
  U64 m;                                    \
  U64 v0 = U8TO64_LE(state);                \
  U64 v1 = U8TO64_LE(state+8);              \
  U64 v2 = U8TO64_LE(state+16);             \
  U64 v3 = U8TO64_LE(state+24);             \
                                            \
  for ( ; in != end; in += 8 )              \
  {                                         \
    m = U8TO64_LE( in );                    \
    v3 ^= m;                                \
                                            \
    SIP_ROUNDS;                             \
                                            \
    v0 ^= m;                                \
  }                                         \
                                            \
  switch( left )                            \
  {                                         \
  case 7: b |= ( ( U64 )in[ 6] )  << 48; /*FALLTHROUGH*/    \
  case 6: b |= ( ( U64 )in[ 5] )  << 40; /*FALLTHROUGH*/    \
  case 5: b |= ( ( U64 )in[ 4] )  << 32; /*FALLTHROUGH*/    \
  case 4: b |= ( ( U64 )in[ 3] )  << 24; /*FALLTHROUGH*/    \
  case 3: b |= ( ( U64 )in[ 2] )  << 16; /*FALLTHROUGH*/    \
  case 2: b |= ( ( U64 )in[ 1] )  <<  8; /*FALLTHROUGH*/    \
  case 1: b |= ( ( U64 )in[ 0] ); break;    \
  case 0: break;                            \
  }                                         \
                                            \
  v3 ^= b;                                  \
                                            \
  SIP_ROUNDS;                               \
                                            \
  v0 ^= b;                                  \
                                            \
  v2 ^= 0xff;                               \
                                            \
  SIP_FINAL_ROUNDS                          \
                                            \
  b = v0 ^ v1 ^ v2  ^ v3;                   \
  return b;                                 \
}                                           \
                                            \
PERL_STATIC_INLINE U32                      \
FNC ## _with_state                          \
  (const unsigned char * const state, const unsigned char *in, const STRLEN inlen) \
{                                           \
    union {                                 \
        U64 h64;                            \
        U32 h32[2];                         \
    } h;                                    \
    h.h64= FNC ## _with_state_64(state,in,inlen); \
    return h.h32[0] ^ h.h32[1];             \
}                                           \
                                            \
                                            \
PERL_STATIC_INLINE U32                      \
FNC (const unsigned char * const seed, const unsigned char *in, const STRLEN inlen) \
{                                                                   \
    U64 state[4];                                                   \
    SIPHASH_SEED_STATE(seed,state[0],state[1],state[2],state[3]);   \
    return FNC ## _with_state((U8*)state,in,inlen);                 \
}


PERL_SIPHASH_FNC(
    S_perl_hash_siphash_1_3
    ,SIPROUND;
    ,SIPROUND;SIPROUND;SIPROUND;
)

PERL_SIPHASH_FNC(
    S_perl_hash_siphash_2_4
    ,SIPROUND;SIPROUND;
    ,SIPROUND;SIPROUND;SIPROUND;SIPROUND;
)

#endif /* defined(CAN64BITHASH) */