我的处理器 (Intel i7) 支持 POPCNT 指令
,我想从我的 C# 应用程序中调用它。这可能吗?
我相信我在某处读到它不是,但是如果 JIT 发现它可用,它会调用它,但是我必须调用什么函数可以用这样的指令代替?
Popcount 在一个循环中被调用了数百万次,所以如果可能的话,我希望能够进行这种 CPU 优化。
最佳答案
你想玩火,我们这里喜欢玩火...
class Program
{
const uint PAGE_EXECUTE_READWRITE = 0x40;
const uint MEM_COMMIT = 0x1000;
[DllImport("kernel32.dll", SetLastError = true)]
static extern IntPtr VirtualAlloc(IntPtr lpAddress, IntPtr dwSize, uint flAllocationType, uint flProtect);
private delegate int IntReturner();
static void Main(string[] args)
{
List<byte> bodyBuilder = new List<byte>();
bodyBuilder.Add(0xb8); // MOV EAX,
bodyBuilder.AddRange(BitConverter.GetBytes(42)); // 42
bodyBuilder.Add(0xc3); // RET
byte[] body = bodyBuilder.ToArray();
IntPtr buf = VirtualAlloc(IntPtr.Zero, (IntPtr)body.Length, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
Marshal.Copy(body, 0, buf, body.Length);
IntReturner ptr = (IntReturner)Marshal.GetDelegateForFunctionPointer(buf, typeof(IntReturner));
Console.WriteLine(ptr());
}
}
(这个小的汇编示例将简单地返回 42...我认为这是这个答案的完美数字:-))
最后的诀窍是:
A) 你必须知道你要写的asm对应的操作码
B) 你使用 VirtualAlloc 使一页内存可执行
C) 你以某种方式在那里复制你的操作码
(代码取自http://www.cnblogs.com/netact/archive/2013/01/10/2855448.html)
好的...另一个是网站上写的(减去 uint
-> IntPtr dwSize
上的错误),这个应该是这样的写的(或者至少它比原来的+1...我会把所有东西都封装在一个IDisposable
类中而不是使用try...finally
)
class Program
{
const uint PAGE_READWRITE = 0x04;
const uint PAGE_EXECUTE = 0x10;
const uint MEM_COMMIT = 0x1000;
const uint MEM_RELEASE = 0x8000;
[DllImport("kernel32.dll", SetLastError = true)]
static extern IntPtr VirtualAlloc(IntPtr lpAddress, IntPtr dwSize, uint flAllocationType, uint flProtect);
[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool VirtualProtect(IntPtr lpAddress, IntPtr dwSize, uint flAllocationType, out uint lpflOldProtect);
[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool VirtualFree(IntPtr lpAddress, IntPtr dwSize, uint dwFreeType);
private delegate int IntReturner();
static void Main(string[] args)
{
List<byte> bodyBuilder = new List<byte>();
bodyBuilder.Add(0xb8); // MOV EAX,
bodyBuilder.AddRange(BitConverter.GetBytes(42)); // 42
bodyBuilder.Add(0xc3); // RET
byte[] body = bodyBuilder.ToArray();
IntPtr buf = IntPtr.Zero;
try
{
// We VirtualAlloc body.Length bytes, with R/W access
// Note that from what I've read, MEM_RESERVE is useless
// if the first parameter is IntPtr.Zero
buf = VirtualAlloc(IntPtr.Zero, (IntPtr)body.Length, MEM_COMMIT, PAGE_READWRITE);
if (buf == IntPtr.Zero)
{
throw new Win32Exception();
}
// Copy our instructions in the buf
Marshal.Copy(body, 0, buf, body.Length);
// Change the access of the allocated memory from R/W to Execute
uint oldProtection;
bool result = VirtualProtect(buf, (IntPtr)body.Length, PAGE_EXECUTE, out oldProtection);
if (!result)
{
throw new Win32Exception();
}
// Create a delegate to the "function"
// Sadly we can't use Funct<int>
var fun = (IntReturner)Marshal.GetDelegateForFunctionPointer(buf, typeof(IntReturner));
Console.WriteLine(fun());
}
finally
{
if (buf != IntPtr.Zero)
{
// Free the allocated memory
bool result = VirtualFree(buf, IntPtr.Zero, MEM_RELEASE);
if (!result)
{
throw new Win32Exception();
}
}
}
}
}
关于c# - 如何从 C# 调用 CPU 指令?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/29040550/