namespace ComponentAce.Compression.Libs.zlib;

internal sealed class Adler32
{
	private const int BASE = 65521;

	private const int NMAX = 5552;

	internal long adler32(long adler, byte[] buf, int index, int len)
	{
		if (buf == null)
		{
			return 1L;
		}
		long num = adler & 0xFFFF;
		long num2 = (adler >> 16) & 0xFFFF;
		while (len > 0)
		{
			int num3 = ((len < 5552) ? len : 5552);
			len -= num3;
			while (num3 >= 16)
			{
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num += buf[index++] & 0xFF;
				num2 += num;
				num3 -= 16;
			}
			if (num3 != 0)
			{
				do
				{
					num += buf[index++] & 0xFF;
					num2 += num;
				}
				while (--num3 != 0);
			}
			num %= 65521;
			num2 %= 65521;
		}
		return (num2 << 16) | num;
	}
}