这两天在看C# SIMD相关的东西, 在爆栈上面搜到一段代码, 表示很震惊, 还是得贴出来…
1 [UnmanagedFunctionPointer(CallingConvention.StdCall)] 2 delegate void VectorAddDelegate(float[] C, float[] B, float[] A, int length); 3 4 [DllImport("kernel32.dll", SetLastError = true)] 5 static extern IntPtr VirtualAlloc( 6 IntPtr lpAddress, UIntPtr dwSize, 7 IntPtr flAllocationType, IntPtr flProtect); 8 9 //This array of bytes has been produced from 10 //the SSE assembly version – it is a complete 11 //function that accepts four parameters (three 12 //vectors and length) and adds the vectors 13 14 byte[] sseAssemblyBytes = { 15 0x8b, 0x5c, 0x24, 0x10, 0x8b, 0x74, 0x24, 0x0c, 0x8b, 16 0x7c, 0x24, 0x08, 0x8b, 0x4c, 0x24, 0x04, 0x31, 0xd2, 17 0x0f, 0x10, 0x0c, 0x97, 0x0f, 0x10, 0x04, 0x96, 0x0f, 18 0x58, 0xc8, 0x0f, 0x11, 0x0c, 0x91, 0x83, 0xc2, 0x04, 19 0x39, 0xda, 0x7f, 0xea, 0xc2, 0x10, 0x00 }; 20 21 IntPtr codeBuffer = VirtualAlloc( 22 IntPtr.Zero, new UIntPtr((uint)sseAssemblyBytes.Length), 23 0x1000 | 0x2000, //MEM_COMMIT | MEM_RESERVE 24 0x40 //EXECUTE_READWRITE 25 ); 26 27 Marshal.Copy(sseAssemblyBytes, 0, codeBuffer, sseAssemblyBytes.Length); 28 29 VectorAddDelegate addVectors = (VectorAddDelegate) 30 Marshal.GetDelegateForFunctionPointer(codeBuffer, typeof(VectorAddDelegate)); 31 //We can now use ‘addVectors’ to add vectors!
这段代码里面的sseAssemblyBytes, 实际上是一段汇编代码, 他先把这段汇编代码拷贝到虚拟内存里面去, 然后设置这块内存可以被执行EXECUTE_READWRITE, 从而在这块内存上创建一个函数指针….
虽然这代码不能移植, 但是感觉还是有一点点屌