#include "adler32.h"

// Mark Adler's compact Adler32 hashing algorithm
// Originally from the public domain stb.h header.
uint32_t adler32::update(uint32_t adler, const void* ptr, size_t buf_len)
{
    if (!ptr)
    {
        return NULL;
    }

    const uint8_t* buffer = static_cast<const uint8_t*>(ptr);

    const unsigned long ADLER_MOD = 65521;
    unsigned long s1 = adler & 0xffff, s2 = adler >> 16;
    size_t blocklen;
    unsigned long i;

    blocklen = buf_len % 5552;
    while (buf_len)
    {
        for (i = 0; i + 7 < blocklen; i += 8)
        {
            s1 += buffer[0], s2 += s1;
            s1 += buffer[1], s2 += s1;
            s1 += buffer[2], s2 += s1;
            s1 += buffer[3], s2 += s1;
            s1 += buffer[4], s2 += s1;
            s1 += buffer[5], s2 += s1;
            s1 += buffer[6], s2 += s1;
            s1 += buffer[7], s2 += s1;

            buffer += 8;
        }

        for (; i < blocklen; ++i)
        {
            s1 += *buffer++, s2 += s1;
        }

        s1 %= ADLER_MOD, s2 %= ADLER_MOD;
        buf_len -= blocklen;
        blocklen = 5552;
    }
    return (s2 << 16) + s1;
}