SxGeo diapasons search on C#

private uint SearchDB(byte[] db, uint ipn, uint min, uint max)
{
    if (max - min > 1)
    {
        while (max - min > 8)
        {
            uint offset = (min + max) >> 1;
            uint x = getUintFrom3b(bSubstr(db, offset * Header.block_len, 3));
            if (ipn > getUintFrom3b(bSubstr(db, offset * Header.block_len, 3)))
                min = offset;
            else
                max = offset;
        }

        while (ipn >= getUintFrom3b(bSubstr(db, min * Header.block_len, 3))
            && ++min < max) { }
    }
    else
    {
        min++;
    }

    uint ans = 0;

    if (Header.IdLen == 3) //БД с городами
    {
        ans = getUintFrom3b(
            bSubstr(db, min * Header.block_len - Header.IdLen, Header.IdLen));
    }
    else //только ID стран
    {
        ans = bSubstr(db, min * Header.block_len - Header.IdLen, Header.IdLen)[0];
    }

    return ans;
}