我在各种地方看到过关于使用固定块进行不安全迭代数组有多快的内容。我在.NET 4和4.5中尝试了一下,结果大致相同。
安全比较总是更快,有时候略微快一些,有时候几乎是一半的时间,特别是在.NET 4中。
我做错了什么吗?
class Program
{
public unsafe static int UnsafeCompareTo2(byte[] self, byte[] other)
{
if (self.Length < other.Length) { return -1; }
if (self.Length > other.Length) { return +1; }
GCHandle selfHandle =
GCHandle.Alloc(self, GCHandleType.Pinned);
GCHandle otherHandle =
GCHandle.Alloc(other, GCHandleType.Pinned);
byte* selfPtr = (byte*)
selfHandle.AddrOfPinnedObject().ToPointer();
byte* otherPtr = (byte*)
otherHandle.AddrOfPinnedObject().ToPointer();
int length = self.Length;
int comparison = 0;
for (int index = 0; index < length; index++)
{
comparison =
(*selfPtr++).CompareTo((*otherPtr++));
if (comparison != 0) { break; }
}
selfHandle.Free();
return comparison;
}
public static int CompareTo(byte[] self, byte[] other)
{
if (self.Length < other.Length) { return -1; }
if (self.Length > other.Length) { return +1; }
int comparison = 0;
for (int i = 0; i < self.Length && i < other.Length; i++)
{
if ((comparison = self[i].CompareTo(other[i])) != 0)
{ return comparison; }
}
return comparison;
}
public unsafe static int UnsafeCompareTo(byte[] self, byte[] other)
{
if (self.Length < other.Length) { return -1; }
if (self.Length > other.Length) { return +1; }
int n = self.Length;
fixed (byte* selfPtr = self, otherPtr = other)
{
byte* ptr1 = selfPtr;
byte* ptr2 = otherPtr;
while (n-- > 0)
{
int comparison;
if ((comparison = (*ptr1++).CompareTo(*ptr2++)) != 0)
{
return comparison;
}
}
}
return 0;
}
static void Main(string[] args)
{
byte[] b1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };
byte[] b2 = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21 };
Stopwatch watch = new Stopwatch();
watch.Start();
int result;
for(long i = 0; i < Math.Pow(10, 2); i++)
result = CompareTo(b1, b2);
watch.Stop();
Console.WriteLine("safe = {0}", watch.Elapsed);
watch.Restart();
for (long i = 0; i < Math.Pow(10, 2); i++)
result = UnsafeCompareTo(b1, b2);
watch.Stop();
Console.WriteLine("unsafe1 = {0}", watch.Elapsed);
watch.Restart();
for (long i = 0; i < Math.Pow(10, 2); i++)
result = UnsafeCompareTo2(b1, b2);
watch.Stop();
Console.WriteLine("unsafe2 = {0}", watch.Elapsed);
Console.ReadLine();
}
}