c# - 不安全的指针操作

Question

我正在尝试用 C# 编写一个 CPU 模拟器。机器的对象看起来像这样:

class Machine 
{
    short a,b,c,d; //these are registers.

    short[] ram=new short[0x10000];  //RAM organised as 65536 16-bit words

    public void tick() { ... } //one instruction is processed
}

当我执行一条指令时，我有一个 switch 语句来决定指令的结果将存储在什么地方(寄存器或 RAM 的一个字)

我希望能够做到这一点:

short* resultContainer;

if (destination == register)
{
    switch (resultSymbol) //this is really an opcode, made a char for clarity
    {
       case 'a': resultContainer=&a;
       case 'b': resultContainer=&b;
       //etc
    }
}
else
{
    //must be a place in RAM
    resultContainer = &RAM[location];
}

然后，当我执行指令后，我可以像这样简单地存储结果:

*resultContainer = result;

我一直在努力弄清楚如何在不扰乱 C# 的情况下做到这一点。

我如何使用 unsafe{} 和 fixed(){ } 以及我可能不知道的其他东西来完成此操作？

Answer 1

这就是我的实现方式:

class Machine
{
    short a, b, c, d;
    short[] ram = new short[0x10000];

    enum AddressType
    {
        Register,
        DirectMemory,
    }

    // Gives the address for an operand or for the result.
    // `addressType`and `addrCode` are extracted from instruction opcode
    // `regPointers` and `ramPointer` are fixed pointers to registers and RAM.
    private unsafe short* GetAddress(AddressType addressType, short addrCode, short*[] regPointers, short* ramPointer)
    {
        switch (addressType)
        {
            case AddressType.Register:
                return regPointers[addrCode]; //just an example implementation
            case AddressType.DirectMemory:
                return ramPointer + addrCode; //just an example implementation
            default:
                return null;
        }
    }

    public unsafe void tick()
    {
        fixed (short* ap = &a, bp = &b, cp = &c, dp = &d, ramPointer = ram)
        {
            short*[] regPointers = new short*[] { ap, bp, cp, dp };

            short* pOperand1, pOperand2, pResult;
            AddressType operand1AddrType, operand2AddrType, resultAddrType;
            short operand1AddrCode, operand2AddrCode, resultAddrCode;

            // ... decipher the instruction and extract the address types and codes

            pOperand1 = GetAddress(operand1AddrType, operand1AddrCode, regPointers, ramPointer);
            pOperand2 = GetAddress(operand2AddrType, operand2AddrCode, regPointers, ramPointer);
            pResult = GetAddress(resultAddrType, resultAddrCode, regPointers, ramPointer);

            // execute the instruction, using `*pOperand1` and `*pOperand2`, storing the result in `*pResult`.

        }
    }
}

要获取寄存器和 RAM 数组的地址，您必须使用 fixed 语句。此外，您只能在 fixed block 中使用获取的指针。所以你必须传递指针。