/* Copyright (c) 2019, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <stdint.h>
#include <string.h>

#include <openssl/siphash.h>


static void siphash_round(uint64_t v[4]) {
  v[0] += v[1];
  v[2] += v[3];
  v[1] = (v[1] << 13) | (v[1] >> (64 - 13));
  v[3] = (v[3] << 16) | (v[3] >> (64 - 16));
  v[1] ^= v[0];
  v[3] ^= v[2];
  v[0] = (v[0] << 32) | (v[0] >> 32);
  v[2] += v[1];
  v[0] += v[3];
  v[1] = (v[1] << 17) | (v[1] >> (64 - 17));
  v[3] = (v[3] << 21) | (v[3] >> (64 - 21));
  v[1] ^= v[2];
  v[3] ^= v[0];
  v[2] = (v[2] << 32) | (v[2] >> 32);
}

uint64_t SIPHASH_24(const uint64_t key[2], const uint8_t *input,
                    size_t input_len) {
  const size_t orig_input_len = input_len;

  uint64_t v[4];
  v[0] = key[0] ^ UINT64_C(0x736f6d6570736575);
  v[1] = key[1] ^ UINT64_C(0x646f72616e646f6d);
  v[2] = key[0] ^ UINT64_C(0x6c7967656e657261);
  v[3] = key[1] ^ UINT64_C(0x7465646279746573);

  while (input_len >= sizeof(uint64_t)) {
    uint64_t m;
    memcpy(&m, input, sizeof(m));
    v[3] ^= m;
    siphash_round(v);
    siphash_round(v);
    v[0] ^= m;

    input += sizeof(uint64_t);
    input_len -= sizeof(uint64_t);
  }

  union {
    uint8_t bytes[8];
    uint64_t word;
  } last_block;
  last_block.word = 0;
  memcpy(last_block.bytes, input, input_len);
  last_block.bytes[7] = orig_input_len & 0xff;

  v[3] ^= last_block.word;
  siphash_round(v);
  siphash_round(v);
  v[0] ^= last_block.word;

  v[2] ^= 0xff;
  siphash_round(v);
  siphash_round(v);
  siphash_round(v);
  siphash_round(v);

  return v[0] ^ v[1] ^ v[2] ^ v[3];
}