namespace com.hitrust.util.Checksums
{
    using System;

    public sealed class Adler32 : IChecksum
    {
        private static readonly uint BASE = 0xfff1;
        private uint checksum;

        public Adler32()
        {
            this.Reset();
        }

        public void Reset()
        {
            this.checksum = 1;
        }

        public void Update(int bval)
        {
            uint s1 = this.checksum & 0xffff;
            uint s2 = this.checksum >> 0x10;
            s1 = (uint) ((s1 + (bval & 0xff)) % BASE);
            s2 = (s1 + s2) % BASE;
            this.checksum = (s2 << 0x10) + s1;
        }

        public void Update(byte[] buffer)
        {
            this.Update(buffer, 0, buffer.Length);
        }

        public void Update(byte[] buf, int off, int len)
        {
            if (buf == null)
            {
                throw new ArgumentNullException("buf");
            }
            if (((off < 0) || (len < 0)) || ((off + len) > buf.Length))
            {
                throw new ArgumentOutOfRangeException();
            }
            uint s1 = this.checksum & 0xffff;
            uint s2 = this.checksum >> 0x10;
            while (len > 0)
            {
                int n = 0xed8;
                if (n > len)
                {
                    n = len;
                }
                len -= n;
                while (--n >= 0)
                {
                    s1 += (uint) (buf[off++] & 0xff);
                    s2 += s1;
                }
                s1 = s1 % BASE;
                s2 = s2 % BASE;
            }
            this.checksum = (s2 << 0x10) | s1;
        }

        public long Value
        {
            get
            {
                return (long) this.checksum;
            }
        }
    }
}