add adler32 (as seen in miniz)

[r-lyeh-archived]

mz_ulong mz_adler32(mz_ulong adler, const unsigned char *ptr, size_t buf_len)
{
  mz_uint32 i, s1 = (mz_uint32)(adler & 0xffff), s2 = (mz_uint32)(adler >> 16); size_t block_len = buf_len % 5552;
  if (!ptr) return MZ_ADLER32_INIT;
  while (buf_len) {
    for (i = 0; i + 7 < block_len; i += 8, ptr += 8) {
      s1 += ptr[0], s2 += s1; s1 += ptr[1], s2 += s1; s1 += ptr[2], s2 += s1; s1 += ptr[3], s2 += s1;
      s1 += ptr[4], s2 += s1; s1 += ptr[5], s2 += s1; s1 += ptr[6], s2 += s1; s1 += ptr[7], s2 += s1;
    }
    for ( ; i < block_len; ++i) s1 += *ptr++, s2 += s1;
    s1 %= 65521U, s2 %= 65521U; buf_len -= block_len; block_len = 5552;
  }
  return (s2 << 16) + s1;
}

// Karl Malbrain's compact CRC-32. See "A compact CCITT crc16 and crc32 C implementation that balances processor cache usage against speed": http://www.geocities.com/malbrain/
mz_ulong mz_crc32(mz_ulong crc, const mz_uint8 *ptr, size_t buf_len)
{
  static const mz_uint32 s_crc32[16] = { 0, 0x1db71064, 0x3b6e20c8, 0x26d930ac, 0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
    0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c, 0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c };
  mz_uint32 crcu32 = (mz_uint32)crc;
  if (!ptr) return MZ_CRC32_INIT;
  crcu32 = ~crcu32; while (buf_len--) { mz_uint8 b = *ptr++; crcu32 = (crcu32 >> 4) ^ s_crc32[(crcu32 & 0xF) ^ (b & 0xF)]; crcu32 = (crcu32 >> 4) ^ s_crc32[(crcu32 & 0xF) ^ (b >> 4)]; }
  return ~crcu32;
}

[r-lyeh-archived]

or...

static inline uint32_t ComputeAdler32(unsigned char* data, size_t size) {
    uint32_t a = 1;
    uint32_t b = 0;

    for (size_t i = 0; i < size; i++) {
        a = (a + data[i]) % 65521;
        b = (b + a) % 65521;
    }
    return (b << 16) | a;
}