二分逼近&二分查找 高效解析800万大数据之区域分布

利用二分逼近法(bisection method) ，解析800多万IP 只需几十秒， 比较高效！



原来的顺序查找算法 效率比较低

readonly string ipBinaryFilePath = "qqzengipdb.dat";
readonly byte[] dataBuffer, indexBuffer;
readonly uint[] index = new uint[256];
readonly int dataLength;
public IpLocation()
{
try
{
FileInfo file = new FileInfo(ipBinaryFilePath);
dataBuffer = new byte[file.Length];
using (var fin = new FileStream(file.FullName, FileMode.Open, FileAccess.Read))
{
fin.Read(dataBuffer, 0, dataBuffer.Length);
}
var offset_len = BytesToLong(dataBuffer[0], dataBuffer[1], dataBuffer[2], dataBuffer[3]); //Big Endian
indexBuffer = new byte[offset_len];
Array.Copy(dataBuffer, 4, indexBuffer, 0, offset_len);
dataLength = (int)offset_len;
for (int loop = 0; loop < 256; loop++)
{
//索引 四字节  LITTLE_ENDIAN
index[loop] = BytesToLong(indexBuffer[loop * 4 + 3], indexBuffer[loop * 4 + 2], indexBuffer[loop * 4 + 1], indexBuffer[loop * 4]);
}
}
catch { }
}

public string[] Find(string ip)
{
var ips = ip.Split('.');
uint ip_prefix = uint.Parse(ips[0]);
uint find_uint32 = BytesToLong(byte.Parse(ips[0]), byte.Parse(ips[1]), byte.Parse(ips[2]), byte.Parse(ips[3]));//BIG_ENDIAN

// LITTLE_ENDIAN
int max_len = 0;
int resultOffset =-1;
int resultLegth =-1;

uint start = index[ip_prefix] * 8 + 1024;
if (ip_prefix != 255)
{
max_len = (int)index[ip_prefix + 1] * 8 + 1024;
}
else
{
max_len = (int)index[255] * 8 + 1024+1;
}

for (; start < max_len; start += 8)
{
// 前四位 结束ip   后三位 偏移  最后一位 内容长度
uint endipNum = BytesToLong(indexBuffer[start + 0], indexBuffer[start + 1], indexBuffer[start + 2], indexBuffer[start + 3]);//BIG_ENDIAN
if (endipNum >= find_uint32)
{
resultOffset =(int) BytesToLong((byte)0, indexBuffer[start + 6], indexBuffer[start + 5], indexBuffer[start + 4]);//LITTLE_ENDIAN
resultLegth = 0xFF & indexBuffer[start + 7];// 长度
break;
}
}
if (resultOffset==-1||resultLegth==-1)
{
return new string[] {"N/A"};
}
var areaBytes = new byte[resultLegth];
Array.Copy(dataBuffer, dataLength + resultOffset - 1024, areaBytes, 0, resultLegth);
return Encoding.UTF8.GetString(areaBytes).Split(' ');
}

private static uint BytesToLong(byte a, byte b, byte c, byte d)
{

return ((uint)a << 24) | ((uint)b << 16) | ((uint)c << 8) | (uint)d;
}

public static string long2IP(long longIP)
{
StringBuilder sb = new StringBuilder("");
sb.Append(longIP >> 24);
sb.Append(".");
//将高8位置0，然后右移16为

sb.Append((longIP & 0x00FFFFFF) >> 16);
sb.Append(".");

sb.Append((longIP & 0x0000FFFF) >> 8);
sb.Append(".");
sb.Append((longIP & 0x000000FF));

return sb.ToString();

}
　　
}

改进版 采用二分逼近 算法(类似二分查找，但又不同) 性能提升很大

public string[] Find(string ip)
{
var ips = ip.Split('.');
uint ip_prefix = uint.Parse(ips[0]);
uint find_uint32 = BytesToLong(byte.Parse(ips[0]), byte.Parse(ips[1]), byte.Parse(ips[2]), byte.Parse(ips[3]));//BIG_ENDIAN
uint max_len = 0;
int resultOffset = -1;
int resultLegth = -1;
uint start = index[ip_prefix];
if (ip_prefix != 255)
{
max_len = index[ip_prefix + 1];
}
else
{
max_len = index[255];
}
uint num = max_len - start;
uint my_index = BinarySearch(start, max_len, find_uint32);
start = my_index * 8 + 1024;
resultOffset = (int)BytesToLong((byte)0, indexBuffer[start + 6], indexBuffer[start + 5], indexBuffer[start + 4]);//LITTLE_ENDIAN
resultLegth = 0xFF & indexBuffer[start + 7];// 长度

if (resultOffset == -1 || resultLegth == -1)
{
return new string[] { "N/A" };
}
var areaBytes = new byte[resultLegth];
Array.Copy(dataBuffer, dataLength + resultOffset - 1024, areaBytes, 0, resultLegth);
return Encoding.UTF8.GetString(areaBytes).Split(' ');
}

/// <summary>
/// 二分逼近
/// </summary>
public uint BinarySearch(uint low, uint high, uint k)
{
uint M = 0;
while (low <= high)
{
uint mid = (low + high) / 2;
uint endipNum = GetStartIp(mid);
if (endipNum >= k)
{
M = mid; //mid有可能是解
high = mid - 1;
}
else
low = mid + 1;
}
return M;
}

有了上面高效算法 解析出来800多万数据 也很快 再用一个简单的ling 统计一下即可

var cn_result= from r in list
group r by r.cn into g
select new { key = g.Key, cnt = g.Count() };

800多万数据 统计组图